Re: [RE-wrenches] Fuse sizing in battery circuits
Ray, One thing I didn't understand is how you can pair a 400 amp class-T fuse with a 4/0 cable. The 400 fuse curve looks like the continuous rating is 350A in the graph supplied by Allan. Which is well above the 4/0 ampacity of 250A (copper). Anyone want to explain? thanks, Troy Harvey - Principal Engineer Heliocentric 801-453-9434 tahar...@heliocentric.org On Apr 5, 2013, at 10:12 PM, Ray Walters r...@solarray.com wrote: I just finished a rewire and we kept the Ananda power center, Allan :-) Back when we used class T fuses more they were always over sized relative to Heinemann breakers. 400 amp class T fuse = 250 amp breaker= 4/0 cable 200 amp class T fuse = 175 amp breaker= 2/0 cable I still think class T fuses are superior in some ways to breakers: they have better interrupt capacity and trip faster in a short circuit condition. However, If you spend too much time thinking about and looking at the trip curves, you'll break your brain and special order some weird fuses and breakers. (anybody need a 350 amp class T fuse?) Just follow the inverter manufacturer's recommendations and all will be well. On the other hand, William has brought up a topic I have harped on for years: Having the OCPD in the cabinet doesn't protect the majority of the circuit. Class T fuses at the battery terminals do, but they're not rated for the corrosive environment. I have thrown a few class T fuses away that had acid eating away at the ends. I don't have the solution, but I will continue to point out that this is a real problem. Dropping a wrench across the battery terminals can lead to a spectacular failure that not only can cause a fire, but might even cause a battery explosion, yet NEC offers no protection. We use insulated wrenches from experience, and hope for the best. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/5/2013 8:29 PM, William Miller wrote: Friends: Good topic. Some questions: 1. Most manufacturer's present an installation guide that shows one OCPD in the battery circuit and that is in the BOS cabinet. This means the battery leads are unprotected. Do we need an OPCD at the battery terminals? 2. Class T fuses are generally recommended for this application. The data shows them as fast acting. Is this a problem? Will they act too fast and open during normal surge loads? Thanks in advance! William Miller Troy, Overcurrent device size is matched to the conductor size. The inverse time constant nature of an overcurrent device can typically handle the surge currents as long as conductor sizing has truly been done correctly for the conductor. Circuit breakers are preferred to fuses because they can be reset. There has been volumes written on this issue. The constant current at lowest battery voltage should be used, plus the ac ripple content on the battery circuit. This is usually a much larger conductor than your average designer will plan for. The best thing is to look at Midnight, Outback, and Schneider and see what size overcurrent devices they require for their products. That will give you a good clue as to how to size the conductor and overcurrent device. Bill. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Troy Harvey Sent: Friday, April 05, 2013 3:38 PM To: RE-wrenches Subject: [RE-wrenches] Fuse sizing in battery circuits I've got a question about battery string fusing. Typically we size the wire from the batteries to the inverter based on continuous rating procedures (max power/efficiency)*125%. However a 6kW inverter, can peak at 12kW for 5-10 seconds, doubling the source current. That is no big deal for the wire, because it is a short time frame... little heat will be generated. However, in fusing the sub-strings, you need to account for that peak surge current so you don't blow fuses all the time. But if you put a 500-1000 amp fuse on a 4/0 wire, above the max surge draw of the inverter, the wire will be under-protected for its ampacity rating. Any thoughts on the catch-22? ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
: Good topic. Some questions: 1. Most manufacturer's present an installation guide that shows one OCPD in the battery circuit and that is in the BOS cabinet. This means the battery leads are unprotected. Do we need an OPCD at the battery terminals? 2. Class T fuses are generally recommended for this application. The data shows them as fast acting. Is this a problem? Will they act too fast and open during normal surge loads? Thanks in advance! William Miller Troy, Overcurrent device size is matched to the conductor size. The inverse time constant nature of an overcurrent device can typically handle the surge currents as long as conductor sizing has truly been done correctly for the conductor. Circuit breakers are preferred to fuses because they can be reset. There has been volumes written on this issue. The constant current at lowest battery voltage should be used, plus the ac ripple content on the battery circuit. This is usually a much larger conductor than your average designer will plan for. The best thing is to look at Midnight, Outback, and Schneider and see what size overcurrent devices they require for their products. That will give you a good clue as to how to size the conductor and overcurrent device. Bill. *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Troy Harvey *Sent:* Friday, April 05, 2013 3:38 PM *To:* RE-wrenches *Subject:* [RE-wrenches] Fuse sizing in battery circuits I've got a question about battery string fusing. Typically we size the wire from the batteries to the inverter based on continuous rating procedures (max power/efficiency)*125%. However a 6kW inverter, can peak at 12kW for 5-10 seconds, doubling the source current. That is no big deal for the wire, because it is a short time frame... little heat will be generated. However, in fusing the sub-strings, you need to account for that peak surge current so you don't blow fuses all the time. But if you put a 500-1000 amp fuse on a 4/0 wire, above the max surge draw of the inverter, the wire will be under-protected for its ampacity rating. Any thoughts on the catch-22? ___ List sponsored by Home Power magazine List Address:RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive:http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org mailto:RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
Hi Ray, Not saying he was right, but it was explained to me by an inspector that the pipe electrode mentioned in 250.166(C) is different than a water main. The justification being that 250.52(A)(1) lists requirements for a metal underground water pipe electrode, while 250.52(A)(5) lists pipe electrode separately. I agree a water main fits the description of a pipe, but I suppose it could depend on the mood of the inspector. I've managed to avoid it myself, but have heard horror stories of 4/0 GECs being required by inspectors. Good point about 250.53(D)(2) Supplemental Electrode Required. Although it does list a pipe again as a possible supplemental electrode to the water main. 250.166(C) just seems a little unclear with respect to a water main electrode. I have seen a number of sites that do not have a supplemental electrode in addition to the water main, but I suppose you could simply install a rod, bond it to the water main, and use #6 copper for the DC GEC. Thanks, Garrison -Original Message- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Ray Walters Sent: Tuesday, April 16, 2013 2:22 PM To: RE-wrenches Subject: Re: [RE-wrenches] Fuse sizing in battery circuits First, a water main is no longer allowed to be used as the primary grounding electrode by itself, it needs an additional electrode added to it 25053(D)2. You still are required to bond to it 250.104(A)1, but it doesn't count as the electrode. Also, 250.166 (C) specifically lists pipe as one of the exceptions. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/16/2013 1:06 PM, Garrison Riegel wrote: Hi Ray and All, 250.166 says the GEC must be sized as specified in (A) Not smaller than the neutral conductor, or (B) Not smaller than the largest conductor supplied by the system, except as permitted by (C) through (E). A water main [as in 250.52(A)(1)] is not listed as an exception in (C) through (E). So if the GE is a water main wouldn't the GEC need to be 4/0, if the battery cables were 4/0? Not saying it makes sense, especially if the water main is 3/4, but this has always made me wonder. Thoughts? Garrison Riegel Project Manager | Solar Service Inc [p] 847-677-0950 | garri...@solarserviceinc.com NABCEP Certified PV Installation ProfessionalT -Original Message- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Ray Walters Sent: Tuesday, April 16, 2013 12:52 PM To: RE-wrenches Subject: Re: [RE-wrenches] Fuse sizing in battery circuits Hi Drake; Read down a bit more and 250.166(C) and (D) limit the size of the GEC to #4 or #6 max., depending on what electrode is used. This used to not be the case, and systems in the 90s had 4/0 cable to a 5/8 electrode: which just like your 1/2 pipe example was absolutely ridiculous. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/16/2013 9:31 AM, Drake wrote: So, in a standard battery system, with a charge control, ground fault protection and an array, the DC system will likely need grounding. If the DC system is grounded, then the battery cables are grounded also. In 250.166 (B) it says the grounding electrode conductor (GEC) shall not be smaller than the largest conductor supplied by the system. If the battery cables are supplied by the system doesn't this imply that the GEC should be the size of the battery cable? This is the logic that has led some inspectors to require a 4/0 copper wire to be bonded to a 1/2 water pipe. This is, of course, technically absurd. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
A metal underground water pipe is still a pipe in all cases, so I think I'm missing your inspector's logic. A water main is always going to be made out of pipe, so I think the exception to 250.166 (C) should always apply. (unless some places make them square?;-) ) The difference in pipe between 250.52A1 and A5 is that one is a pipe set in the ground by an electrician with the sole purpose of being a grounding electrode, while the other is used for water and is set by the plumber. The reason I heard that water lines into the house had to have supplementary grounding is that they often transition to PVC and so aren't always continuous metal. They also might be cut and changed later by a plumber. That also was a change from earlier code, that used to allow the water main to be used as the sole grounding electrode. EIther way, 250.166 does not make a distinction, it just says Pipe and would cover all GEC connections. The 4/0 GEC horror stories probably are from earlier editions of the code. BIll Brooks can tell us when that changed. My guess is that it was a pre 2002 code requirement, as I saw that on 90s PV systems. Your final suggested install should be code compliant with all the various NEC sections (IMHO); just use a lay in lug type pipe grounding clamp, to keep the GEC continuous to the rod. Some of this code stuff makes you wonder whether we should have studied law to be a Wrench.(ugh) R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/17/2013 7:44 AM, Garrison Riegel wrote: Hi Ray, Not saying he was right, but it was explained to me by an inspector that the pipe electrode mentioned in 250.166(C) is different than a water main. The justification being that 250.52(A)(1) lists requirements for a metal underground water pipe electrode, while 250.52(A)(5) lists pipe electrode separately. I agree a water main fits the description of a pipe, but I suppose it could depend on the mood of the inspector. I've managed to avoid it myself, but have heard horror stories of 4/0 GECs being required by inspectors. Good point about 250.53(D)(2) Supplemental Electrode Required. Although it does list a pipe again as a possible supplemental electrode to the water main. 250.166(C) just seems a little unclear with respect to a water main electrode. I have seen a number of sites that do not have a supplemental electrode in addition to the water main, but I suppose you could simply install a rod, bond it to the water main, and use #6 copper for the DC GEC. Thanks, Garrison -Original Message- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Ray Walters Sent: Tuesday, April 16, 2013 2:22 PM To: RE-wrenches Subject: Re: [RE-wrenches] Fuse sizing in battery circuits First, a water main is no longer allowed to be used as the primary grounding electrode by itself, it needs an additional electrode added to it 25053(D)2. You still are required to bond to it 250.104(A)1, but it doesn't count as the electrode. Also, 250.166 (C) specifically lists pipe as one of the exceptions. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/16/2013 1:06 PM, Garrison Riegel wrote: Hi Ray and All, 250.166 says the GEC must be sized as specified in (A) Not smaller than the neutral conductor, or (B) Not smaller than the largest conductor supplied by the system, except as permitted by (C) through (E). A water main [as in 250.52(A)(1)] is not listed as an exception in (C) through (E). So if the GE is a water main wouldn't the GEC need to be 4/0, if the battery cables were 4/0? Not saying it makes sense, especially if the water main is 3/4, but this has always made me wonder. Thoughts? Garrison Riegel Project Manager | Solar Service Inc [p] 847-677-0950 | garri...@solarserviceinc.com NABCEP Certified PV Installation ProfessionalT -Original Message- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Ray Walters Sent: Tuesday, April 16, 2013 12:52 PM To: RE-wrenches Subject: Re: [RE-wrenches] Fuse sizing in battery circuits Hi Drake; Read down a bit more and 250.166(C) and (D) limit the size of the GEC to #4 or #6 max., depending on what electrode is used. This used to not be the case, and systems in the 90s had 4/0 cable to a 5/8 electrode: which just like your 1/2 pipe example was absolutely ridiculous. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/16/2013 9:31 AM, Drake wrote: So, in a standard battery system, with a charge control, ground fault protection and an array, the DC system will likely need grounding. If the DC system is grounded, then the battery cables are grounded also. In 250.166 (B) it says
Re: [RE-wrenches] Fuse sizing in battery circuits
This is a fairly complicated issue. I agree that an ungrounded battery system is safer than a grounded one, since the hot wire will not arc to the casing of the enclosure. If a system has a charge control and an array, the negative wire of the array usually needs to be grounded (or have a fuse in each leg). If there is an MPPT charge control, the voltage will almost certainly be over 50 volts. However, supposedly even a 24 volt system with no MPPT can go over 50 V. So, in a standard battery system, with a charge control, ground fault protection and an array, the DC system will likely need grounding. If the DC system is grounded, then the battery cables are grounded also. In 250.166 (B) it says the grounding electrode conductor (GEC) shall not be smaller than the largest conductor supplied by the system. If the battery cables are supplied by the system doesn't this imply that the GEC should be the size of the battery cable? This is the logic that has led some inspectors to require a 4/0 copper wire to be bonded to a 1/2 water pipe. This is, of course, technically absurd. Are a lot of battery based systems now going in with no DC grounding and fuses in both legs? How does a GFP work in this scenario? The Sunny Island is a different animal, as the DC system in it does not connect to the array. It is AC coupled instead of DC coupled. Therefore, it is connected with AC. The connection to the batteries is isolated. So maybe the issue of DC grounding doesn't apply. The DC system in the Sunny Island will, however, normally operate at over 50 volts, unless the batteries are low. What is the bottom line here? At 04:47 PM 4/15/2013, you wrote: Hi August; 250.162(A) says operating at greater than 50 v, which a 48 v nominal system operates most of the time at over 50 v, at least when solar charging and/or selling back. We used to get dinged many years ago for using breakers rated at 50v dc on 48 v systems. John Wiles used to insist we use the highest possible voltage (Voc of modules on coldest day) Personally I prefer ungrounded systems, so I'm not saying there's anything wrong from a safety stand point, just that inspectors here don't see it the same way. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760On 4/15/2013 2:20 PM, August Goers wrote: Hi Drake, The Sunny Island System runs at 48 V nominal so I don't believe 250.162(A) applies. We have some really savvy inspectors in the Bay Area and they were happy for us to be ungrounded since we're operating at 48 V. Yes, the actual voltage might go above 50 V when charging but I believe it is the nominal voltage that the code cares about. Best, ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
Hi Drake; Read down a bit more and 250.166(C) and (D) limit the size of the GEC to #4 or #6 max., depending on what electrode is used. This used to not be the case, and systems in the 90s had 4/0 cable to a 5/8 electrode: which just like your 1/2 pipe example was absolutely ridiculous. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/16/2013 9:31 AM, Drake wrote: So, in a standard battery system, with a charge control, ground fault protection and an array, the DC system will likely need grounding. If the DC system is grounded, then the battery cables are grounded also. In 250.166 (B) it says the grounding electrode conductor (GEC) shall not be smaller than the largest conductor supplied by the system. If the battery cables are supplied by the system doesn't this imply that the GEC should be the size of the battery cable? This is the logic that has led some inspectors to require a 4/0 copper wire to be bonded to a 1/2 water pipe. This is, of course, technically absurd. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
Ray, Thanks for the note and I see your point about operating at greater than 50 v. Does anyone else have an opinion on the operating voltage for batteries? I know that NEC 480.2 defines the nominal battery voltage as 2 volts per cell for lead-acid and I believe I have a code interpretation book lying around that states that this is what you apply to 250.162 but I don't have much info other than that. Best, August *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto: re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Ray Walters *Sent:* Monday, April 15, 2013 1:48 PM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] Fuse sizing in battery circuits Hi August; 250.162(A) says operating at greater than 50 v, which a 48 v nominal system operates most of the time at over 50 v, at least when solar charging and/or selling back. We used to get dinged many years ago for using breakers rated at 50v dc on 48 v systems. John Wiles used to insist we use the highest possible voltage (Voc of modules on coldest day) Personally I prefer ungrounded systems, so I'm not saying there's anything wrong from a safety stand point, just that inspectors here don't see it the same way. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/15/2013 2:20 PM, August Goers wrote: Hi Drake, The Sunny Island System runs at 48 V nominal so I don't believe 250.162(A) applies. We have some really savvy inspectors in the Bay Area and they were happy for us to be ungrounded since we're operating at 48 V. Yes, the actual voltage might go above 50 V when charging but I believe it is the nominal voltage that the code cares about. Best, ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
Hi Ray, Thanks for that information. I'm glad they covered that. I never install more than a #4. The question I'm still not sure of is weather or not we need to ground the DC. I always have run a GEC to the DC. It would be great if we didn't need to do so on the Sunny Islands especially, since they are not set up for DC grounding. Drake At 01:51 PM 4/16/2013, you wrote: Hi Drake; Read down a bit more and 250.166(C) and (D) limit the size of the GEC to #4 or #6 max., depending on what electrode is used. This used to not be the case, and systems in the 90s had 4/0 cable to a 5/8 electrode: which just like your 1/2 pipe example was absolutely ridiculous. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/16/2013 9:31 AM, Drake wrote: So, in a standard battery system, with a charge control, ground fault protection and an array, the DC system will likely need grounding. If the DC system is grounded, then the battery cables are grounded also. In 250.166 (B) it says the grounding electrode conductor (GEC) shall not be smaller than the largest conductor supplied by the system. If the battery cables are supplied by the system doesn't this imply that the GEC should be the size of the battery cable? This is the logic that has led some inspectors to require a 4/0 copper wire to be bonded to a 1/2 water pipe. This is, of course, technically absurd. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
Hi Ray and All, 250.166 says the GEC must be sized as specified in (A) Not smaller than the neutral conductor, or (B) Not smaller than the largest conductor supplied by the system, except as permitted by (C) through (E). A water main [as in 250.52(A)(1)] is not listed as an exception in (C) through (E). So if the GE is a water main wouldn't the GEC need to be 4/0, if the battery cables were 4/0? Not saying it makes sense, especially if the water main is 3/4, but this has always made me wonder. Thoughts? Garrison Riegel Project Manager | Solar Service Inc [p] 847-677-0950 | garri...@solarserviceinc.com NABCEP Certified PV Installation ProfessionalT -Original Message- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Ray Walters Sent: Tuesday, April 16, 2013 12:52 PM To: RE-wrenches Subject: Re: [RE-wrenches] Fuse sizing in battery circuits Hi Drake; Read down a bit more and 250.166(C) and (D) limit the size of the GEC to #4 or #6 max., depending on what electrode is used. This used to not be the case, and systems in the 90s had 4/0 cable to a 5/8 electrode: which just like your 1/2 pipe example was absolutely ridiculous. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/16/2013 9:31 AM, Drake wrote: So, in a standard battery system, with a charge control, ground fault protection and an array, the DC system will likely need grounding. If the DC system is grounded, then the battery cables are grounded also. In 250.166 (B) it says the grounding electrode conductor (GEC) shall not be smaller than the largest conductor supplied by the system. If the battery cables are supplied by the system doesn't this imply that the GEC should be the size of the battery cable? This is the logic that has led some inspectors to require a 4/0 copper wire to be bonded to a 1/2 water pipe. This is, of course, technically absurd. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
First, a water main is no longer allowed to be used as the primary grounding electrode by itself, it needs an additional electrode added to it 25053(D)2. You still are required to bond to it 250.104(A)1, but it doesn't count as the electrode. Also, 250.166 (C) specifically lists pipe as one of the exceptions. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/16/2013 1:06 PM, Garrison Riegel wrote: Hi Ray and All, 250.166 says the GEC must be sized as specified in (A) Not smaller than the neutral conductor, or (B) Not smaller than the largest conductor supplied by the system, except as permitted by (C) through (E). A water main [as in 250.52(A)(1)] is not listed as an exception in (C) through (E). So if the GE is a water main wouldn't the GEC need to be 4/0, if the battery cables were 4/0? Not saying it makes sense, especially if the water main is 3/4, but this has always made me wonder. Thoughts? Garrison Riegel Project Manager | Solar Service Inc [p] 847-677-0950 | garri...@solarserviceinc.com NABCEP Certified PV Installation ProfessionalT -Original Message- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Ray Walters Sent: Tuesday, April 16, 2013 12:52 PM To: RE-wrenches Subject: Re: [RE-wrenches] Fuse sizing in battery circuits Hi Drake; Read down a bit more and 250.166(C) and (D) limit the size of the GEC to #4 or #6 max., depending on what electrode is used. This used to not be the case, and systems in the 90s had 4/0 cable to a 5/8 electrode: which just like your 1/2 pipe example was absolutely ridiculous. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/16/2013 9:31 AM, Drake wrote: So, in a standard battery system, with a charge control, ground fault protection and an array, the DC system will likely need grounding. If the DC system is grounded, then the battery cables are grounded also. In 250.166 (B) it says the grounding electrode conductor (GEC) shall not be smaller than the largest conductor supplied by the system. If the battery cables are supplied by the system doesn't this imply that the GEC should be the size of the battery cable? This is the logic that has led some inspectors to require a 4/0 copper wire to be bonded to a 1/2 water pipe. This is, of course, technically absurd. ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
Hi Drake, The Sunny Island System runs at 48 V nominal so I don't believe 250.162(A) applies. We have some really savvy inspectors in the Bay Area and they were happy for us to be ungrounded since we're operating at 48 V. Yes, the actual voltage might go above 50 V when charging but I believe it is the nominal voltage that the code cares about. Best, August *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto: re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Drake *Sent:* Saturday, April 13, 2013 12:14 PM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] Fuse sizing in battery circuits Is it possible that not grounding the DC on an inverter could be code compliant? In the past, we were always required to install grounding electrode conductors to the DC negative, as required for grounding Direct Current systems (250 VIII). Maybe grounding can be eliminated in a purely AC coupled system due to the fact that the system is not supplying premise wiring. Maybe the DC can be considered as an integral part of the system supplying the AC. The rules for grounding DC are stated below. 250.162 Direct current Circuits and Systems to Be Grounded (A) Two-Wire, Direct-Current Systems. A 2-wire, dc system supplying premises wiring and operating at greater than 50 volts but not greater than 300 volts shall be grounded. Exception No. 1: A system equipped with a ground detector and supplying only industrial equipment in limited areas shall not be required to be grounded. Exception No. 2: A rectifier-derived dc system supplied from an ac system complying with 250.20 shall not be required to be grounded. Exception No. 3: Direct-current fire alarm circuits having a maximum current of 0.030 ampere as specified in Article 760, Part III, shall not be required to be grounded. In a Sunny Island system there is no charge control, nothing else in the DC besides the battery and battery cables. Does not grounding the negative really meet code requirements in the US ? Are the inverter cables not considered to be premise wiring? Thanks, Drake At 03:56 PM 4/10/2013, you wrote: Content-Class: urn:content-classes:message Content-Language: en-US Content-Type: multipart/alternative; boundary=_000_B448FC9E37458B469E77EA0BB954AD4702BD99AC6Emailbox01_ August: The SI can run with an ungrounded battery or a grounded battery. With the internal breaker it is set up for a negative ground battery. I believe the manual says ground at the battery terminal. If you chose to go ungrounded you will need to have an OCPD in both battery + and battery – (all ungrounded conductors). I am pretty sure the SI is not internally bonded to ground. This is normal in the rest of the world. Mine are running with an ungrounded battery and there isolation between battery and ground. Best Regards, John Berdner General Manager, North America SolarEdge Technologies, Inc. 3347 Gateway Boulevard, Fremont CA 94538 USA *(*Please note of our new address.)* T: 510.498.3200, X 747 M: 530.277.4894 *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.orgre-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *August Goers *Sent:* Wednesday, April 10, 2013 9:45 AM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] Fuse sizing in battery circuits Hi All - As a slightly separate topic, should we fuse both the positive and negative battery lines with an SMA Sunny Island? I believe that the negative is grounded so should not be fused but I've heard conflicting stories from tech support. Thanks, August *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.orgre-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Drake *Sent:* Wednesday, April 10, 2013 5:52 AM *To:* RE-wrenches *Subject:* Re: [RE-wrenches] Fuse sizing in battery circuits boB, SMA does recommend protecting Sunny Islands with a fuse on the battery, even though the breakers on the units are rated for 10,000 Amps. Are the SI breakers inferior others you have mentioned? Thanks, Drake At 12:14 AM 4/10/2013, you wrote: After 100's of thousands of inverters having been shipped in the last many years and thousands of inverters broken and shorting the battery terminals, there has never been (to our knowledge) one breaker that has not tripped. The Midnite site lists the AIC rating of all our breakers I believe. The Carling F series of Magnetic-Hydraulic breakers poop sheet is here... http://www.carlingtech.com/sites/default/files/documents/F-Series_Details_%26_COS_0.pdf I guess there isn't a graph of AIC vs. voltage on their F series web page but we remember them showing us figures or a graph that says those breakers have an AIC of more than 100,000 amps at 48 volts. We'll try to find that info or you may be able to get that from Carling. I have, many times, directly connected these breakers across good L-16 battery strings to demonstrate the left-hand rule to people where the 4/0
Re: [RE-wrenches] Fuse sizing in battery circuits
Hi August; 250.162(A) says operating at greater than 50 v, which a 48 v nominal system operates most of the time at over 50 v, at least when solar charging and/or selling back. We used to get dinged many years ago for using breakers rated at 50v dc on 48 v systems. John Wiles used to insist we use the highest possible voltage (Voc of modules on coldest day) Personally I prefer ungrounded systems, so I'm not saying there's anything wrong from a safety stand point, just that inspectors here don't see it the same way. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/15/2013 2:20 PM, August Goers wrote: Hi Drake, The Sunny Island System runs at 48 V nominal so I don't believe 250.162(A) applies. We have some really savvy inspectors in the Bay Area and they were happy for us to be ungrounded since we're operating at 48 V. Yes, the actual voltage might go above 50 V when charging but I believe it is the nominal voltage that the code cares about. Best, ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
Are AC coupled systems with no DC loads exempted from the grounding rules of DC coupled, battery based systems and the rules of DC grounding? This is from the Sunny Island Manual: External grounding of the negative pole of the batteries is possible, because the batteries and the grid side are galvanically isolated within the Sunny Island. Dimenssion the crossâsection of the protective conductor sufficiently. Thus you are ensuring that in the event of a fault the high currents occurring can be discharged with an external grounding. If groounding of the negative pole of the battery is necessary, assemble this outside of the Sunny Island. As far as I am aware, the NEC code is kind of vague on grounding battery banks (please correct me if I am wrong), it is more of a AHJ requirement. There is no reference to ground (DC side) inside the SI. SMA America, LLC Steve Jefferson Supervisor, Service Line 6020 West Oaks Blvd, Suite 300 Rocklin, CA 95765 - 3714 U.S.A. Tel: +1 916 625 0870 Fax: +1 916 624-2445 Service Line +1 877 697 6283 (Toll Free) Email: steve.jeffer...@sma-america.com http://www.sma-america.com/www.SMA-America.com This email and any attachments thereto may contain SMA America, LLC confidential, privileged and private material for the sole use of the intended recipient. Any review, copying, or distribution of this email (or any attachments thereto) by others is strictly prohibited. If you are not the intended recipient, please contact the sender immediately and permanently delete the original and any copies of this email and any attachments thereto. Thank you. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of August Goers Sent: Wednesday, April 10, 2013 2:13 PM To: RE-wrenches Subject: Re: [RE-wrenches] Fuse sizing in battery circuits Steve, So if we wanted to ground the negative would we literally run a ground wire to one of the battery terminals? Is there anything in the NEC that governs this? What are the deciding factors when deciding to ground the negative or not? As a separate note, I've noticed that the negative battery terminals measure 0 volts to ground on a Sunny Island setup once everything is connected without any extra grounding added. I thought that there must be some reference to ground happening in the Sunny Island but apparently I'm wrong. Thanks, August From: mailto:re-wrenches-boun...@lists.re-wrenches.orgre-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Steve Jefferson Sent: Wednesday, April 10, 2013 9:56 AM To: RE-wrenches Subject: Re: [RE-wrenches] Fuse sizing in battery circuits If the Batt negative is not bonded to ground, then yes SMA recommends fusing both Positive and Negative. Also, the negative is not bonded to ground internally in the Sunny Island. SMA America, LLC Steve Jefferson Supervisor, Service Line 6020 West Oaks Blvd, Suite 300 Rocklin, CA 95765 - 3714 U.S.A. Tel: +1 916 625 0870 Fax: +1 916 624-2445 Service Line +1 877 697 6283 (Toll Free) Email: mailto:steve.jeffer...@sma-america.comsteve.jeffer...@sma-america.com www.SMA-America.com ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
If the Batt negative is not bonded to ground, then yes SMA recommends fusing both Positive and Negative. Also, the negative is not bonded to ground internally in the Sunny Island. SMA America, LLC Steve Jefferson Supervisor, Service Line 6020 West Oaks Blvd, Suite 300 Rocklin, CA 95765 - 3714 U.S.A. Tel: +1 916 625 0870 Fax: +1 916 624-2445 Service Line +1 877 697 6283 (Toll Free) Email: steve.jeffer...@sma-america.com www.SMA-America.comhttp://www.sma-america.com/ This email and any attachments thereto may contain SMA America, LLC confidential, privileged and private material for the sole use of the intended recipient. Any review, copying, or distribution of this email (or any attachments thereto) by others is strictly prohibited. If you are not the intended recipient, please contact the sender immediately and permanently delete the original and any copies of this email and any attachments thereto. Thank you. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of August Goers Sent: Wednesday, April 10, 2013 9:45 AM To: RE-wrenches Subject: Re: [RE-wrenches] Fuse sizing in battery circuits Hi All - As a slightly separate topic, should we fuse both the positive and negative battery lines with an SMA Sunny Island? I believe that the negative is grounded so should not be fused but I've heard conflicting stories from tech support. Thanks, August From: re-wrenches-boun...@lists.re-wrenches.orgmailto:re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.orgmailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Drake Sent: Wednesday, April 10, 2013 5:52 AM To: RE-wrenches Subject: Re: [RE-wrenches] Fuse sizing in battery circuits boB, SMA does recommend protecting Sunny Islands with a fuse on the battery, even though the breakers on the units are rated for 10,000 Amps. Are the SI breakers inferior others you have mentioned? Thanks, Drake At 12:14 AM 4/10/2013, you wrote: After 100's of thousands of inverters having been shipped in the last many years and thousands of inverters broken and shorting the battery terminals, there has never been (to our knowledge) one breaker that has not tripped. The Midnite site lists the AIC rating of all our breakers I believe. The Carling F series of Magnetic-Hydraulic breakers poop sheet is here... http://www.carlingtech.com/sites/default/files/documents/F-Series_Details_%26_COS_0.pdf I guess there isn't a graph of AIC vs. voltage on their F series web page but we remember them showing us figures or a graph that says those breakers have an AIC of more than 100,000 amps at 48 volts. We'll try to find that info or you may be able to get that from Carling. I have, many times, directly connected these breakers across good L-16 battery strings to demonstrate the left-hand rule to people where the 4/0 cable jumps apart or towards each other when very high current passes through those wires when they are near each other. It always trips. Never tried it at anything above a 48V battery banks IIRC. Robin would like to mention that anyone that wants to use T-Classc fuses Welcome back to the 1990's boB On 4/9/2013 1:23 PM, Ray Walters wrote: Hey Bob; Can you share that AIC vs Voltage chart? Thanks, R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/9/2013 1:46 PM, boB wrote: Those 250 amp and 175 amp breakers we have used for many many years now have an AIC of 50,000 amps at 125 volts and if you look at the curve, at 48 volts they are around 100,000 amps. I think that this information is on the label of the breaker. How many problems have you had with the Carlings or any other type of those large breakers ? boB On 4/9/2013 10:40 AM, Michael Welch wrote: If anyone would like an Acrobat version of this article, you can find it here: ftp://ftp.re-wrenches.org/pub/hp27_pg26_freitas.pdf William Dorsett wrote at 07:00 AM 4/9/2013: This topic comes up often enough that we ought to mention a yellowed article in Home Power, (1992 Issue 27, pg 26). Christopher Freitas wrote Overcurrent Protection for Battery-Powered Systems where he describes experiments he did back when he was with Ananda. He put a 2000 A Big Switch to initiate a short (4/0 cable) between the terminals on a set of four golf cart batteries (2 strings @ 12V). In series, he put in a 500A Shunt so he could measure current passing and various fuses and breakers. For comparison, we decided to directly short the battery...the meter read 6960 amps peak current (three seconds) ...during each test the 4/0 cable lifted off the ground 4 inches into the air by the forces generated by the extremely high current.. They videoed the 250 A ANN buss fuses arc and smoke; the 200A Heinemann Series AM breakers (paralleled ones that maybe Roy mentioned) went 3 seconds without breaking
Re: [RE-wrenches] Fuse sizing in battery circuits
August: The SI can run with an ungrounded battery or a grounded battery. With the internal breaker it is set up for a negative ground battery. I believe the manual says ground at the battery terminal. If you chose to go ungrounded you will need to have an OCPD in both battery + and battery - (all ungrounded conductors). I am pretty sure the SI is not internally bonded to ground. This is normal in the rest of the world. Mine are running with an ungrounded battery and there isolation between battery and ground. Best Regards, John Berdner General Manager, North America SolarEdge Technologies, Inc. 3347 Gateway Boulevard, Fremont CA 94538 USA (*Please note of our new address.) T: 510.498.3200, X 747 M: 530.277.4894 From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of August Goers Sent: Wednesday, April 10, 2013 9:45 AM To: RE-wrenches Subject: Re: [RE-wrenches] Fuse sizing in battery circuits Hi All - As a slightly separate topic, should we fuse both the positive and negative battery lines with an SMA Sunny Island? I believe that the negative is grounded so should not be fused but I've heard conflicting stories from tech support. Thanks, August From: re-wrenches-boun...@lists.re-wrenches.orgmailto:re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.orgmailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Drake Sent: Wednesday, April 10, 2013 5:52 AM To: RE-wrenches Subject: Re: [RE-wrenches] Fuse sizing in battery circuits boB, SMA does recommend protecting Sunny Islands with a fuse on the battery, even though the breakers on the units are rated for 10,000 Amps. Are the SI breakers inferior others you have mentioned? Thanks, Drake At 12:14 AM 4/10/2013, you wrote: After 100's of thousands of inverters having been shipped in the last many years and thousands of inverters broken and shorting the battery terminals, there has never been (to our knowledge) one breaker that has not tripped. The Midnite site lists the AIC rating of all our breakers I believe. The Carling F series of Magnetic-Hydraulic breakers poop sheet is here... http://www.carlingtech.com/sites/default/files/documents/F-Series_Details_%26_COS_0.pdf I guess there isn't a graph of AIC vs. voltage on their F series web page but we remember them showing us figures or a graph that says those breakers have an AIC of more than 100,000 amps at 48 volts. We'll try to find that info or you may be able to get that from Carling. I have, many times, directly connected these breakers across good L-16 battery strings to demonstrate the left-hand rule to people where the 4/0 cable jumps apart or towards each other when very high current passes through those wires when they are near each other. It always trips. Never tried it at anything above a 48V battery banks IIRC. Robin would like to mention that anyone that wants to use T-Classc fuses Welcome back to the 1990's boB On 4/9/2013 1:23 PM, Ray Walters wrote: Hey Bob; Can you share that AIC vs Voltage chart? Thanks, R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/9/2013 1:46 PM, boB wrote: Those 250 amp and 175 amp breakers we have used for many many years now have an AIC of 50,000 amps at 125 volts and if you look at the curve, at 48 volts they are around 100,000 amps. I think that this information is on the label of the breaker. How many problems have you had with the Carlings or any other type of those large breakers ? boB On 4/9/2013 10:40 AM, Michael Welch wrote: If anyone would like an Acrobat version of this article, you can find it here: ftp://ftp.re-wrenches.org/pub/hp27_pg26_freitas.pdf William Dorsett wrote at 07:00 AM 4/9/2013: This topic comes up often enough that we ought to mention a yellowed article in Home Power, (1992 Issue 27, pg 26). Christopher Freitas wrote Overcurrent Protection for Battery-Powered Systems where he describes experiments he did back when he was with Ananda. He put a 2000 A Big Switch to initiate a short (4/0 cable) between the terminals on a set of four golf cart batteries (2 strings @ 12V). In series, he put in a 500A Shunt so he could measure current passing and various fuses and breakers. For comparison, we decided to directly short the battery...the meter read 6960 amps peak current (three seconds) ...during each test the 4/0 cable lifted off the ground 4 inches into the air by the forces generated by the extremely high current.. They videoed the 250 A ANN buss fuses arc and smoke; the 200A Heinemann Series AM breakers (paralleled ones that maybe Roy mentioned) went 3 seconds without breaking and the video showed a flash and blue smoke. 175A ITE breaker with 42,000 AIC simply tripped...but still allowed a peak current of 2960 amps 200A Class T Littlefuse opened promptly with no external signs
Re: [RE-wrenches] Fuse sizing in battery circuits
to that same bus bar. It has some advantages, as individual strings can be monitored and serviced without taking the entire system down. FWIW, OutBack makes a battery rack for AGM batteries with series string overcurrent and disconnects on every string. It's also to my knowledge the first UL1741 Listed device available -- the other stuff I've seen is either not listed, or is trading on old 508a standards. AGMs might not be for every installation, but for jobs where they are appropriate this could be a good, code-compliant solution. Phil Undercuffler OutBack Power On Friday, April 5, 2013, Ray Walters wrote: I just finished a rewire and we kept the Ananda power center, Allan :-) Back when we used class T fuses more they were always over sized relative to Heinemann breakers. 400 amp class T fuse = 250 amp breaker= 4/0 cable 200 amp class T fuse = 175 amp breaker= 2/0 cable I still think class T fuses are superior in some ways to breakers: they have better interrupt capacity and trip faster in a short circuit condition. However, If you spend too much time thinking about and looking at the trip curves, you'll break your brain and special order some weird fuses and breakers. (anybody need a 350 amp class T fuse?) Just follow the inverter manufacturer's recommendations and all will be well. On the other hand, William has brought up a topic I have harped on for years: Having the OCPD in the cabinet doesn't protect the majority of the circuit. Class T fuses at the battery terminals do, but they're not rated for the corrosive environment. I have thrown a few class T fuses away that had acid eating away at the ends. I don't have the solution, but I will continue to point out that this is a real problem. Dropping a wrench across the battery terminals can lead to a spectacular failure that not only can cause a fire, but might even cause a battery explosion, yet NEC offers no protection. We use insulated wrenches from experience, and hope for the best. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/5/2013 8:29 PM, William Miller wrote: Friends: Good topic. Some questions: 1. Most manufacturer's present an installation guide that shows one OCPD in the battery circuit and that is in the BOS cabinet. This means the battery leads are unprotected. Do we need an OPCD at the battery terminals? 2. Class T fuses are generally recommended for this application. The data shows them as fast acting. Is this a problem? Will they act too fast and open during normal surge loads? Thanks in advance! William Miller Troy, Overcurrent device size is matched to the conductor size. The inverse time constant nature of an overcurrent device can typically handle the surge currents as long as conductor sizing has truly been done correctly for the conductor. Circuit breakers are preferred to fuses because they can be reset. There has been volumes written on this issue. The constant current at lowest battery voltage should be used, plus the ac ripple content on the battery circuit. This is usually a much larger conductor than your average designer will plan for. The best thing is to look at Midnight, Outback, and Schneider and see what size overcurrent devices they require for their products. That will give you a good clue as to how to size the conductor and overcurrent device. Bill. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Troy Harvey Sent: Friday, April 05, 2013 3:38 PM To: RE-wrenches Subject: [RE-wrenches] Fuse sizing in battery circuits I've got a question about battery string fusing. Typically we size the wire from the batteries to the inverter based on continuous rating procedures (max power/efficiency)*125%. However a 6kW inverter, can peak at 12kW for 5-10 seconds, doubling the source current. That is no big deal for the wire, because it is a short time frame... little heat will be generated. However, in fusing the sub-strings, you need to account for that peak surge current so you don't blow fuses all the time. But if you put a 500-1000 amp fuse on a 4/0 wire, above the max surge draw of the inverter, the wire will be under-protected for its ampacity rating. Any thoughts on the catch-22? ___ List sponsored by Home Power magazine List Address: mailto:RE-wrenches@lists.re-wrenches.orgRE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.orghttp://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.orghttp://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: http://www.re-wrenches.org/etiquette.htmwww.re-wrenches.org/etiquette.htm Check
Re: [RE-wrenches] Fuse sizing in battery circuits
If anyone would like an Acrobat version of this article, you can find it here: ftp://ftp.re-wrenches.org/pub/hp27_pg26_freitas.pdf William Dorsett wrote at 07:00 AM 4/9/2013: This topic comes up often enough that we ought to mention a yellowed article in Home Power, (1992 Issue 27, pg 26). Christopher Freitas wrote Overcurrent Protection for Battery-Powered Systems where he describes experiments he did back when he was with Ananda. He put a 2000 A Big Switch to initiate a short (4/0 cable) between the terminals on a set of four golf cart batteries (2 strings @ 12V). In series, he put in a 500A Shunt so he could measure current passing and various fuses and breakers. For comparison, we decided to directly short the battery the meter read 6960 amps peak current (three seconds) during each test the 4/0 cable lifted off the ground 4 inches into the air by the forces generated by the extremely high current.. They videoed the 250 A ANN buss fuses arc and smoke; the 200A Heinemann Series AM breakers (paralleled ones that maybe Roy mentioned) went 3 seconds without breaking and the video showed a flash and blue smoke. 175A ITE breaker with 42,000 AIC simply tripped but still allowed a peak current of 2960 amps 200A Class T Littlefuse opened promptly with no external signs of stress 1920 amps peak current Christophers recommendations: Every AE system must have overcurrent protection able to interrupt the maximum current available from the batteries. For most systems, the main protection should use current limiting high AIC fuses, such as a Class T or Class R. A disconnect switch which allows the fuse to be safely changed should be included. A lower cost alternative is to mount the fuse in a fuse holder without a disconnect. Although the fuse would always be electrically hot, it normally would not be changed during the life of the system. The fuse holder should be mounted outside the battery enclosure. Fuses should not be bolted directly onto the battery terminal, as they are not designed to handle the physical stresses that can occur without the protection of a fuse holder. Fuses which have exposed elements, such as ANN fuses, should not be used because they are not current limiting and have only 2500 amps AIC. They also may be a significant hazard when installed near batteries. High AIC breakers, like the Heinemann Series CF (25,000 Amps AIC @ 65VDC) can provide overcurrent protection for individual items. They cannot be used to protect lower AIC breakers. This eliminates their use as a main disconnect in most systems. Low AIC breakers, like the Heinemann Series AM (5000A AIC @65 VDC) or the Square-D QO (5000A @ 125 VDC) can be used in load distribution centers and components, but must be protected by a current limiting fuse. Using low-AIC breakers alone will not provide sufficient protection with a battery system and may be a significant hazard during short circuit situations. It wont pull up anymore on HPs article search but probably Michael has a copy he could post for those interested. Bill Dorsett ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
Those 250 amp and 175 amp breakers we have used for many many years now have an AIC of 50,000 amps at 125 volts and if you look at the curve, at 48 volts they are around 100,000 amps. I think that this information is on the label of the breaker. How many problems have you had with the Carlings or any other type of those large breakers ? boB On 4/9/2013 10:40 AM, Michael Welch wrote: If anyone would like an Acrobat version of this article, you can find it here: ftp://ftp.re-wrenches.org/pub/hp27_pg26_freitas.pdf ftp://ftp.re-wrenches.org/pub/hp27_pg26_freitas.pdfWilliam Dorsett wrote at 07:00 AM 4/9/2013: This topic comes up often enough that we ought to mention a yellowed article in Home Power, (1992 Issue 27, pg 26). Christopher Freitas wrote /Overcurrent Protection for Battery-Powered Systems /where he describes experiments he did back when he was with Ananda. He put a 2000 A Big Switch to initiate a short (4/0 cable) between the terminals on a set of four golf cart batteries (2 strings @ 12V). In series, he put in a 500A Shunt so he could measure current passing and various fuses and breakers. For comparison, we decided to directly short the battery...the meter read 6960 amps peak current (three seconds) ...during each test the 4/0 cable lifted off the ground 4 inches into the air by the forces generated by the extremely high current.. They videoed the 250 A ANN buss fuses arc and smoke; the 200A Heinemann Series AM breakers (paralleled ones that maybe Roy mentioned) went 3 seconds without breaking and the video showed a flash and blue smoke. 175A ITE breaker with 42,000 AIC simply tripped...but still allowed a peak current of 2960 amps 200A Class T Littlefuse opened promptly with no external signs of stress...1920 amps peak current Christopher's recommendations: Every AE system must have overcurrent protection able to interrupt the maximum current available from the batteries. For most systems, the main protection should use current limiting high AIC fuses, such as a Class T or Class R. A disconnect switch which allows the fuse to be safely changed should be included. A lower cost alternative is to mount the fuse in a fuse holder without a disconnect. Although the fuse would always be electrically hot, it normally would not be changed during the life of the system. The fuse holder should be mounted outside the battery enclosure. Fuses should not be bolted directly onto the battery terminal, as they are not designed to handle the physical stresses that can occur without the protection of a fuse holder. Fuses which have exposed elements, such as ANN fuses, should not be used because they are not current limiting and have only 2500 amps AIC. They also may be a significant hazard when installed near batteries. High AIC breakers, like the Heinemann Series CF (25,000 Amps AIC @ 65VDC) can provide overcurrent protection for individual items. They cannot be used to protect lower AIC breakers. This eliminates their use as a main disconnect in most systems. Low AIC breakers, like the Heinemann Series AM (5000A AIC @65 VDC) or the Square-D QO (5000A @ 125 VDC) can be used in load distribution centers and components, but must be protected by a current limiting fuse. Using low-AIC breakers alone will not provide sufficient protection with a battery system and may be a significant hazard during short circuit situations. It won't pull up anymore on HP's article search but probably Michael has a copy he could post for those interested./ / Bill Dorsett ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
Allan, that is a good graph. Thanks. The time vs current is way different than whst I've seen from fuse charts in the past. I'd rather use DC-breakers, but I'm having trouble finding 350AMP DC breakers for 350MCM cable. Any resources? thanks, Troy Harvey - Principal Engineer Heliocentric 801-453-9434 tahar...@heliocentric.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
Ray,
690 does offer the protection, it's just that most maufacturers haven't
made it easy.
690.71 Installation
(C) Current Limiting. A listed, current-limiting, overcurrent device shall
be installed in each circuit adjacent to the batteries where the available
short-circuit current from a battery or battery bank exceeds the
interrupting or withstand ratings of other equipment in that circuit. The
installation of current-limiting fuses shall comply with 690.16.
The telcom industry has been doing this for years. Their norm is to have
each string of batteries on a shelf, and terminate at a breaker. Each
string then is combined at a bus bar or plate, to help ensure equal current
on each string. The loads and charging sources all come to that same bus
bar. It has some advantages, as individual strings can be monitored and
serviced without taking the entire system down.
FWIW, OutBack makes a battery rack for AGM batteries with series string
overcurrent and disconnects on every string. It's also to my knowledge the
first UL1741 Listed device available -- the other stuff I've seen is either
not listed, or is trading on old 508a standards. AGMs might not be for
every installation, but for jobs where they are appropriate this could be a
good, code-compliant solution.
Phil Undercuffler
OutBack Power
On Friday, April 5, 2013, Ray Walters wrote:
I just finished a rewire and we kept the Ananda power center, Allan :-)
Back when we used class T fuses more they were always over sized relative
to Heinemann breakers.
400 amp class T fuse = 250 amp breaker= 4/0 cable
200 amp class T fuse = 175 amp breaker= 2/0 cable
I still think class T fuses are superior in some ways to breakers: they
have better interrupt capacity and trip faster in a short circuit condition.
However, If you spend too much time thinking about and looking at the trip
curves, you'll break your brain and special order some weird fuses and
breakers. (anybody need a 350 amp class T fuse?)
Just follow the inverter manufacturer's recommendations and all will be
well.
On the other hand, William has brought up a topic I have harped on for
years: Having the OCPD in the cabinet doesn't protect the majority of the
circuit. Class T fuses at the battery terminals do, but they're not rated
for the corrosive environment. I have thrown a few class T fuses away that
had acid eating away at the ends.
I don't have the solution, but I will continue to point out that this is a
real problem. Dropping a wrench across the battery terminals can lead to a
spectacular failure that not only can cause a fire, but might even cause a
battery explosion, yet NEC offers no protection.
We use insulated wrenches from experience, and hope for the best.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 4/5/2013 8:29 PM, William Miller wrote:
Friends:
Good topic. Some questions:
1. Most manufacturer's present an installation guide that shows one OCPD
in the battery circuit and that is in the BOS cabinet. This means the
battery leads are unprotected. Do we need an OPCD at the battery terminals?
2. Class T fuses are generally recommended for this application. The data
shows them as fast acting. Is this a problem? Will they act too fast
and open during normal surge loads?
Thanks in advance!
William Miller
Troy,
Overcurrent device size is matched to the conductor size. The inverse time
constant nature of an overcurrent device can typically handle the surge
currents as long as conductor sizing has truly been done correctly for the
conductor. Circuit breakers are preferred to fuses because they can be
reset.
There has been volumes written on this issue. The constant current at
lowest battery voltage should be used, plus the ac ripple content on the
battery circuit. This is usually a much larger conductor than your average
designer will plan for. The best thing is to look at Midnight, Outback, and
Schneider and see what size overcurrent devices they require for their
products. That will give you a good clue as to how to size the conductor
and overcurrent device.
Bill.
*From:* re-wrenches-boun...@lists.re-wrenches.org javascript:_e({},
'cvml', 're-wrenches-boun...@lists.re-wrenches.org'); [
mailto:re-wrenches-boun...@lists.re-wrenches.org javascript:_e({},
'cvml', 're-wrenches-boun...@lists.re-wrenches.org');] *On Behalf Of *Troy
Harvey
*Sent:* Friday, April 05, 2013 3:38 PM
*To:* RE-wrenches
*Subject:* [RE-wrenches] Fuse sizing in battery circuits
I've got a question about battery string fusing. Typically we size the
wire from the batteries to the inverter based on continuous rating
procedures (max power/efficiency)*125%.
However a 6kW inverter, can peak at 12kW for 5-10 seconds, doubling the
source current. That is no big deal for the wire, because it is a short
time frame... little heat will be generated
Re: [RE-wrenches] Fuse sizing in battery circuits
loads?
Thanks in advance!
William Miller
Troy,
Overcurrent device size is matched to the conductor size. The
inverse time constant nature of an overcurrent device can
typically handle the surge currents as long as conductor sizing
has truly been done correctly for the conductor. Circuit
breakers are preferred to fuses because they can be reset.
There has been volumes written on this issue. The constant
current at lowest battery voltage should be used, plus the ac
ripple content on the battery circuit. This is usually a much
larger conductor than your average designer will plan for. The
best thing is to look at Midnight, Outback, and Schneider and
see what size overcurrent devices they require for their
products. That will give you a good clue as to how to size the
conductor and overcurrent device.
Bill.
*From:* re-wrenches-boun...@lists.re-wrenches.org
javascript:_e({}, 'cvml',
're-wrenches-boun...@lists.re-wrenches.org');
[mailto:re-wrenches-boun...@lists.re-wrenches.org
javascript:_e({}, 'cvml',
're-wrenches-boun...@lists.re-wrenches.org');] *On Behalf Of
*Troy Harvey
*Sent:* Friday, April 05, 2013 3:38 PM
*To:* RE-wrenches
*Subject:* [RE-wrenches] Fuse sizing in battery circuits
I've got a question about battery string fusing. Typically we
size the wire from the batteries to the inverter based on
continuous rating procedures (max power/efficiency)*125%.
However a 6kW inverter, can peak at 12kW for 5-10 seconds,
doubling the source current. That is no big deal for the wire,
because it is a short time frame... little heat will be
generated. However, in fusing the sub-strings, you need to
account for that peak surge current so you don't blow fuses all
the time. But if you put a 500-1000 amp fuse on a 4/0 wire,
above the max surge draw of the inverter, the wire will be
under-protected for its ampacity rating. Any thoughts on the
catch-22?
___
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[RE-wrenches] Fuse sizing in battery circuits
I've got a question about battery string fusing. Typically we size the wire from the batteries to the inverter based on continuous rating procedures (max power/efficiency)*125%. However a 6kW inverter, can peak at 12kW for 5-10 seconds, doubling the source current. That is no big deal for the wire, because it is a short time frame... little heat will be generated. However, in fusing the sub-strings, you need to account for that peak surge current so you don't blow fuses all the time. But if you put a 500-1000 amp fuse on a 4/0 wire, above the max surge draw of the inverter, the wire will be under-protected for its ampacity rating. Any thoughts on the catch-22? thanks, Troy Harvey - Principal Engineer Heliocentric 801-453-9434 tahar...@heliocentric.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
Friends: Good topic. Some questions: 1. Most manufacturer's present an installation guide that shows one OCPD in the battery circuit and that is in the BOS cabinet. This means the battery leads are unprotected. Do we need an OPCD at the battery terminals? 2. Class T fuses are generally recommended for this application. The data shows them as fast acting. Is this a problem? Will they act too fast and open during normal surge loads? Thanks in advance! William Miller Troy, Overcurrent device size is matched to the conductor size. The inverse time constant nature of an overcurrent device can typically handle the surge currents as long as conductor sizing has truly been done correctly for the conductor. Circuit breakers are preferred to fuses because they can be reset. There has been volumes written on this issue. The constant current at lowest battery voltage should be used, plus the ac ripple content on the battery circuit. This is usually a much larger conductor than your average designer will plan for. The best thing is to look at Midnight, Outback, and Schneider and see what size overcurrent devices they require for their products. That will give you a good clue as to how to size the conductor and overcurrent device. Bill. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Troy Harvey Sent: Friday, April 05, 2013 3:38 PM To: RE-wrenches Subject: [RE-wrenches] Fuse sizing in battery circuits I've got a question about battery string fusing. Typically we size the wire from the batteries to the inverter based on continuous rating procedures (max power/efficiency)*125%. However a 6kW inverter, can peak at 12kW for 5-10 seconds, doubling the source current. That is no big deal for the wire, because it is a short time frame... little heat will be generated. However, in fusing the sub-strings, you need to account for that peak surge current so you don't blow fuses all the time. But if you put a 500-1000 amp fuse on a 4/0 wire, above the max surge draw of the inverter, the wire will be under-protected for its ampacity rating. Any thoughts on the catch-22? ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Fuse sizing in battery circuits
I just finished a rewire and we kept the Ananda power center, Allan :-) Back when we used class T fuses more they were always over sized relative to Heinemann breakers. 400 amp class T fuse = 250 amp breaker= 4/0 cable 200 amp class T fuse = 175 amp breaker= 2/0 cable I still think class T fuses are superior in some ways to breakers: they have better interrupt capacity and trip faster in a short circuit condition. However, If you spend too much time thinking about and looking at the trip curves, you'll break your brain and special order some weird fuses and breakers. (anybody need a 350 amp class T fuse?) Just follow the inverter manufacturer's recommendations and all will be well. On the other hand, William has brought up a topic I have harped on for years: Having the OCPD in the cabinet doesn't protect the majority of the circuit. Class T fuses at the battery terminals do, but they're not rated for the corrosive environment. I have thrown a few class T fuses away that had acid eating away at the ends. I don't have the solution, but I will continue to point out that this is a real problem. Dropping a wrench across the battery terminals can lead to a spectacular failure that not only can cause a fire, but might even cause a battery explosion, yet NEC offers no protection. We use insulated wrenches from experience, and hope for the best. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 4/5/2013 8:29 PM, William Miller wrote: Friends: Good topic. Some questions: 1. Most manufacturer's present an installation guide that shows one OCPD in the battery circuit and that is in the BOS cabinet. This means the battery leads are unprotected. Do we need an OPCD at the battery terminals? 2. Class T fuses are generally recommended for this application. The data shows them as fast acting. Is this a problem? Will they act too fast and open during normal surge loads? Thanks in advance! William Miller Troy, Overcurrent device size is matched to the conductor size. The inverse time constant nature of an overcurrent device can typically handle the surge currents as long as conductor sizing has truly been done correctly for the conductor. Circuit breakers are preferred to fuses because they can be reset. There has been volumes written on this issue. The constant current at lowest battery voltage should be used, plus the ac ripple content on the battery circuit. This is usually a much larger conductor than your average designer will plan for. The best thing is to look at Midnight, Outback, and Schneider and see what size overcurrent devices they require for their products. That will give you a good clue as to how to size the conductor and overcurrent device. Bill. *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Troy Harvey *Sent:* Friday, April 05, 2013 3:38 PM *To:* RE-wrenches *Subject:* [RE-wrenches] Fuse sizing in battery circuits I've got a question about battery string fusing. Typically we size the wire from the batteries to the inverter based on continuous rating procedures (max power/efficiency)*125%. However a 6kW inverter, can peak at 12kW for 5-10 seconds, doubling the source current. That is no big deal for the wire, because it is a short time frame... little heat will be generated. However, in fusing the sub-strings, you need to account for that peak surge current so you don't blow fuses all the time. But if you put a 500-1000 amp fuse on a 4/0 wire, above the max surge draw of the inverter, the wire will be under-protected for its ampacity rating. Any thoughts on the catch-22? ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Change email address settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
