I always use breakers more because they are easy to reset and visible if tripped. And if a class T fuse blows, you don’t actually know it and then you have the situation of having to go out to replace a $100 fuse or have the customer replace a fuse with live ends which I stopped doing a long time ago.
I wonder if midnite power is going to build a combiner box with breakers. I’m sure the breakers used in their batteries are way less expensive than the big 250’s we have used. I’d sure like to see one. A question on the Class T fuses. Is it UL ok to mount the fuses not in a fuse holder? Like to a buss bar? jay > On Jul 16, 2025, at 5:23 AM, Jason Szumlanski via RE-wrenches > <[email protected]> wrote: > > I like the Midnite 1000/2000A battery combiners for this purpose. The 250A DC > breakers are not cheap, but they add a level of convenience and protection > that I think it worthwhile. > > > Jason Szumlanski > Principal Solar Designer | Florida Solar Design Group > NABCEP Certified Solar Professional (PVIP) > Florida State Certified Solar Contractor CVC56956 > Florida Certified Electrical Contractor EC13013208 > > > On Tue, Jul 15, 2025 at 1:36 PM William Miller via RE-wrenches > <[email protected] > <mailto:[email protected]>> wrote: >> Kirk: >> >> First of all, I apologize for the typo in the subject line. I fixed it. I >> take my writing seriously but sometimes my devices fight me with >> autocorrect. >> >> You make good point regarding a scenario with a battery combiner. Relying on >> multiple BMSs for OCP would be a bad choice. >> >> Fortunately some cabinets come with breakers and those should be sufficient. >> >> William Miller >> Miller Solar.com >> 805-438-5600 >> www.millersolar.com <http://www.millersolar.com/> >> >> >> On Tue, Jul 15, 2025 at 9:50 AM Kirk Herander <[email protected]> wrote: >>> Hello William- >>> >>> I agree with your approach. >>> >>> I never historically have OCPD'ed lead acids at both ends of the battery >>> cable run, but do now, esp. with high kwh LFP, where a DC combiner is in >>> use. >>> >>> For instance, I had to design a 2000 ADC bus @ a nominal 55 vdc, for a 500 >>> kwh Blue Ion LFP bank. To create enough space for cables and fuses, I >>> started with -2- 2000A Midnite combiners, using one for positive and one >>> for negative. >>> >>> Class T fuses are bolted directly to the DC bus (properly sized copper from >>> copper.org <http://copper.org/> charts), and the BI BMS breaker protects at >>> each respective battery cabinet. >>> >>> Same thing on the DC to inverter cables, class T's bolted to the bus, to >>> its respective outback Radian, where the standard 175A breaker resides. >>> >>> I would never again do a building power system of any type or size without >>> both ends of a power cable (point of use & point of origin) being >>> protected, A best practice IMO. >>> >>> >>> >>> On Tue, Jul 15, 2025 at 1:13 AM William Miller via RE-wrenches >>> <[email protected] >>> <mailto:[email protected]>> wrote: >>>> Friends: >>>> >>>> When I design a lead-acid battery system I decide if I need over-current >>>> protection right at the battery or not. My logic is: if the leads are >>>> short, don’t go through a wall and are well protected, I can rely on OCPD >>>> in the BOS cabinets. If any of these criteria is a no I put appropriately >>>> rated class T fuses right at the battery. >>>> >>>> I’m thinking that since BMS devices have over-current protection baked-in, >>>> fusing at the battery would not be necessary for BMS equipped batteries in >>>> any case. Do you agree with that premise? >>>> >>>> >>>> William Miller >>>> Miller Solar.com >>>> 805-438-5600 >>>> www.millersolar.com <http://www.millersolar.com/> >>>> _______________________________________________ >>>> List sponsored by Redwood Alliance >>>> >>>> Pay optional member dues here: http://re-wrenches.org >>>> <http://re-wrenches.org/> >>>> >>>> List Address: [email protected] >>>> <mailto:[email protected]> >>>> >>>> Change listserver email address & settings: >>>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >>>> >>>> There are two list archives for searching. When one doesn't work, try the >>>> other: >>>> https://www.mail-archive.com/[email protected]/ >>>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >>>> >>>> List rules & etiquette: >>>> http://www.re-wrenches.org/etiquette.htm >>>> >>>> Check out or update participant bios: >>>> http://www.members.re-wrenches.org <http://www.members.re-wrenches.org/> >>>> >>> >>> >>> >>> -- >>> >>> >>> <> >>> Kirk Herander / <>[email protected] <mailto:[email protected]> >>> Owner|Principal, VT Solar, LLC >>> Celebrating our 34st Anniversary 1991-2025!! >>> dba Vermont Solar Engineering >>> 802.559.1225 >> _______________________________________________ >> List sponsored by Redwood Alliance >> >> Pay optional member dues here: http://re-wrenches.org >> <http://re-wrenches.org/> >> >> List Address: [email protected] >> <mailto:[email protected]> >> >> Change listserver email address & settings: >> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >> >> There are two list archives for searching. When one doesn't work, try the >> other: >> https://www.mail-archive.com/[email protected]/ >> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >> >> List rules & etiquette: >> http://www.re-wrenches.org/etiquette.htm >> >> Check out or update participant bios: >> http://www.members.re-wrenches.org <http://www.members.re-wrenches.org/> >> > _______________________________________________ > List sponsored by Redwood Alliance > > Pay optional member dues here: http://re-wrenches.org > > List Address: [email protected] > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > There are two list archives for searching. 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