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go-transit-further asked

Reverse Polarity light

Hello all, new to the community. Just finshed my electrical system on my 2020 Transit buildout. I have a Multiplus 3000 12v, 3x100 Ah Battleborn batteries, an Orion Tr-smart, and an Onan 2800i generator. I do not have solar, since I have a Dometic 13,500btu A/C unit. Ok, here's the issue; everything works fine, however, when the Multiplus switches to Charge mode my Blue Sea AC panel "Reverse Polarity" light comes on. Everything still works, no popped breakers, no funny smells, nothing else unusual. When the MP swithes back to Inverter mode, the light goes off. Should I worry, is the Multiplus suspect?

Multiplus-II
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Trevor Bird answered ·

Hello @Go_Transit_Further. I sometimes see this on boats when a significant current is drawn from the AC mains. When your MP is in charge mode, it draws a fair amount of current from the mains. If the mains cable or the connections to the outlet feeding the mains cable allows some voltage drop on the neutral conductor, the reverse polarity light can be illuminated. The reason is the reverse polarity light senses voltage between neutral and ground. If the neutral develops some voltage because of voltage drop on the feed from the M.E.N. point, the voltage can cause the light to dimly glow.

When you use the inverter the mains is isolated so no voltages is sensed between neutral and ground.

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go-transit-further avatar image go-transit-further commented ·
OK, thanks for the quick response, but more importantly should I be concerned? This a new build, and I'm a novice on this stuff, so I am still trying to figure things out. Would I expect/check for a short in my shore connection, the transfer switch, or the Multiplus. Or could it be the outlet to the house which is what I was connected to?
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Trevor Bird answered ·

@Go_Transit_Further .....it is a bit hard to comment from a distance as systems can be complex so I don't want to give you any absolute advice in case it is wrong.....but....if you find that the reverse polarity light only comes on when you put heavy load on the mains input to your system ( for instance when you start your AC system) , you can be pretty convinced the scenario I previously outlined exists. If that happened to my facility I wouldn't be too concerned about it. If you have any doubt, you should have a licensed electrician check it out.

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