The link didn’t work for me yesterday, but I did read it just now. I think we agree more or less – I said the only way I would think about breaking the AC and DC ground connection is with a whole boat ELCI, which seems like what you suggest as well. Galvanic isolators went through three generations I think. The first ones were just diodes, then big capacitors got added in case the diodes failed, and now the newest ones have a monitoring system added so you know if they fail. I am a bit uptight about this stuff because I used to be in the boat wiring business and got many a shock from poorly wired boats. One boat just about killed me and I wasn’t even on it! I was on the floating dock and the air conditioning kicked on. The exhaust water landed on my leg and I got shocked bad enough to knock me over. Someone had swapped the white, black and the green wires around in the connections to the air conditioning pump. There is some confusion too about safe on the boat and safe under the boat. Imagine a boat with an air conditioner and a water heater. There is a lot of AC power flowing in a damp environment through devices made of metal with salt water in them. Imagine they have some leakage to their metal cases. If the green wire ground system is good all the way back to shore with no high resistance connections, there should be no voltage on these devices. All the leakage current should be carried back to the shore ground. There is no good direct path for the AC leakage current to get into the water, although some might do so through salt water damp paths. The danger to people swimming is pretty low, but the danger to people on the boat is directly related to how good the shore ground is. The worse the ground is, the more voltage there is between the devices and the DC grounded parts of the boat. Worst case is you get a lethal shock from touching one of them. When the AC and DC ground systems are connected, that danger is gone. All the ground points on the boat are going to be at the same potential. The danger now shifts to anyone in the water near the boat. Even with a perfect AC ground on shore, it is a long way away and the water is right there. The amount of AC in the water increases with the resistance of the AC shore ground system. You now moved the danger point from inside to outside. It does not even take a lot of current to drown someone, you don’t need to stop their heart, just disrupt their muscles enough so they can’t swim. The ELCI guards against danger to swimmers by tripping when there is leakage. Only issue is an old boat with crap wiring and old equipment may well leak enough to set one off constantly.
Joe Coquina BTW, I will no longer dive on boats that are plugged into shore power and usually insisted the neighbors on either side disconnect too. I also jump in BC full, so if I get shocked right away at least I am floating around getting shocked and can complain loudly!!!! BTW PT 2 – The USA standard 120/240 volt grounded neutral system is *terrible* for a boat. It was invented more than a century ago with lightning protection in mind for long wires on poles. AFAIK commercial ships use isolated ground AC systems, 440V 3 phase I think. From: CnC-List [mailto:[email protected]] On Behalf Of Dreuge via CnC-List Sent: Monday, June 03, 2019 6:12 PM To: [email protected] Cc: Dreuge <[email protected]> Subject: Re: Stus-List [EXTERNAL] Re: Galvanic Isolators Joe, I think there is some confusion. I’m also guessing that you did not follow the link and read my more detailed blog discussion. I don’t blame your reaction, I would have reacted the same way a little while back. I disagree with this. I have had a galvanic isolator since about 1995 or so. Mercury Marine sold them to keep their outdrives from dissolving back then and I grabbed one. I can go on for a while about how they work, but the short version is every boat at the marina is wired together by the ground wires and is essentially one giant boat. If your neighbors don?t have zincs, no problem, your zinc will cover for them! It may not last long doing triple duty though ? The galvanic isolator prevents this from happening. First off, I did not argue that galvanic isolators do not work. They do. I stated that the connection of AC and DC grounds is a main factor leading to galvanic corrosion and thus the need for galvanic isolation. The only reason for connecting the grounds is to provide an effective ground-fault current path. Eliminate the need for an effective ground-fault current path, eliminates the need to connect the grounds. Newer technologies provide such a means. I argued that connecting AC and DC grounds is not needed for ground fault protection if the vessel is protected by a ground fault circuit interrupter(ELCI). This why the ABYC E-11 now requires all new vessels to have such a device. The European ISO requirements (see extract from ISO 13297 in my blog discussion) specifically states that if a RCD (another name for ELCI or GFCI) or isolation transformer is installed then '' the negative ground terminal of the DC system need not be connected to the AC shore ground'' . I'm guessing the ABYC will eventually follow the ISO. My main point is that it is wise to install a whole-vessel ELCI. These provide greater safety, and these are now readily available and more affordable than fail-safe GIs. The Blue Seas A-Series ELCI Main Circuit Breaker (model 3106100) which fits my Blue Seas panel costs under $150. Fail-safe GIs cost well over $300. My very robust under $10 DYI GI was installed in what I called a ‘’Fail-Safe installation’’. That is, it was installed between the AC and DC grounds rather than breaking the AC ground to shore and inserting there. The DYI GI, like the Yardina GI, is not technically a ''fail-safe’’ GI, Yardina claims that they have no reports of their GI failing. While these are very unlikely to fail, if it does fail, it does not matter. The only reason I have not yet removed my DYI GI and AC/DC ground connection is that it does not matter. Your discussion below is not correct . Specifically, the statement of ''deadly hazard ‘’. A GFCI/ELCI would cut the power saving one from the deadly hazard. But even without GFCI/ELCI protection, it is more deadly to have a hot wire in one hand and then touch the DC ground if the AC/DC grounds are connected then if they are not connected. That is, a deadly AC current would flow better to the AC ground with the AC/DC ground wire than it would with just an engine to seawater to AC ground connection. The actual reason for connecting the grounds is less for someone on the vessel and more for the safety of swimmers. Yes, it is wise for a vessel without a main ELCI to connect the AC/DC grounds and if doing so then it is smart to use a GI. I would rather rephrase the last statement: it is unwise nowadays for a vessel with AC shore power connection to not have a whole-vessel ELCI. There is a reason why fewer companies are making fail-safe GI. I initially wondered why a company like Blue Seas, which provides practically any electrical need, does not provide a galvanic isolator. But they do have this discussion on their website: https://www.bluesea.com/support/articles/AC_Circuits/88/Green_Wire_%5BControversy%5D<https://protect2.fireeye.com/url?k=e4d3d3fa-b845825f-e4d3fa8d-0cc47adc5e34-e4153303ea1b3adc&q=1&u=https%3A%2F%2Fwww.bluesea.com%2Fsupport%2Farticles%2FAC_Circuits%2F88%2FGreen_Wire_%5BControversy%5D>. For convenience, here is my original link: http://svjohannarose.blogspot.com/search/label/GalvanicIsolator<https://protect2.fireeye.com/url?k=21887946-7d1e28e3-21885031-0cc47adc5e34-e7040f274d46e876&q=1&u=http%3A%2F%2Fsvjohannarose.blogspot.com%2Fsearch%2Flabel%2FGalvanicIsolator%253Chttps%3A%2F%2Fprotect2.fireeye.com%2Furl%3Fk%3D8c302211-d0a614f2-8c300b66-0cc47adc5fec-d02e08d2e81cb3ec%26q%3D1%26u%3Dhttp%253A%252F%252Fsvjohannarose.blogspot.com%252Fsearch%252Flabel%252FGalvanicIsolator%253E> As far as not grounding the AC system to ships ground, this would be a large and dangerous violation of ABYC regs and they exist for a reason. In a perfect world boats would have isolated 2 wire AC systems with no grounding at all. This is not the case presently and as long as various AC devices not built specifically for boats exist we have to deal with potential ground issues. Do not forget that the shoreside AC power *is not isolated* and you are floating in a more or less direct connection to the ground rod at the transformer and/or panel on shore. If some defective appliance puts AC voltage on any part accessible by a human you now have a hot wire in one hand and any part of the boats DC ground system is the other half of the circuit. This can be a deadly hazard on a boat depending on how good the green wire system on the boat and marina is and even if it is good you still can get a considerable charge through you. The interconnected grounds prevent this from happening. The ONLY way I could see trying to make an isolated AC system besides for an isolation transformer, which is actually a great idea but big and heavy, is if the BOAT had an ELCI installed. You cannot count on every marina having one at their end. Joe Coquina C&C 35 MK I - Paul E. 1981 C&C Landfall 38 S/V Johanna Rose Fort Walton Beach, FL http://svjohannarose.blogspot.com/<https://protect2.fireeye.com/url?k=dae74499-8671153c-dae76dee-0cc47adc5e34-beb80921fa56c64e&q=1&u=http%3A%2F%2Fsvjohannarose.blogspot.com%2F> From: CnC-List [mailto:[email protected]] On Behalf Of Dreuge via CnC-List Sent: Sunday, June 02, 2019 4:07 PM To: [email protected]<mailto:[email protected]> Cc: Dreuge <[email protected]<mailto:[email protected]>> Subject: [EXTERNAL] Re: Stus-List Galvanic Isolators I would not spend much money on a galvanic isolator (GI). The main cause of the galvanic corrosion is a result of connecting the AC and DC grounds. Check if you have these grounds connected. Most older and smaller vessels don?t have the grounds connected and don?t have galvanic corrosion problem. Also, the industry is moving away from this requirement. One is better off investing in a whole vessel GFCI breaker(also called an ELCI Main Circuit Breaker). These cost much less than a typical fail-safe GI and provide galvanic isolation from stray AC currents by disconnecting the power, and more importantly they provide much better ground fault protection than connecting AC & DC grounds. If one still prefers bonding the AC & DC grounds then I would recommend the Yandina GI or better, a DYI GI, and connect the GI between the AC to DC connection to provide a fail-safe connection. I have a write up on my blog about this and also how to make a DYI GI, but in short, don?t waste money on an expensive GI, invest your money in an ELCI breaker, individual GFCI circuit protectors, and a decent marine charger (not a cheap HF/Walmart/Amazon brand ) http://svjohannarose.blogspot.com/search/label/GalvanicIsolator<https://protect2.fireeye.com/url?k=db9d8f89-870bde2c-db9da6fe-0cc47adc5e34-78541a9175b7bc1b&q=1&u=http%3A%2F%2Fsvjohannarose.blogspot.com%2Fsearch%2Flabel%2FGalvanicIsolator%253Chttps%3A%2F%2Fprotect2.fireeye.com%2Furl%3Fk%3D8c302211-d0a614f2-8c300b66-0cc47adc5fec-d02e08d2e81cb3ec%26q%3D1%26u%3Dhttp%253A%252F%252Fsvjohannarose.blogspot.com%252Fsearch%252Flabel%252FGalvanicIsolator%253E>
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