Main AC breaker trips on shore power only?

[CptBacardi]

Hi! The drama continues. I was on shore power using a heat gun to shrink wrap some butt connectors and the main AC breaker tripped. It tripped again when I tried to turn it back on. I turned off all breakers in that circuit and tried the main again, and it stays on. I show 120v when doing that. If I turn on ANY breaker in that circuit, even if it’s not being used, the main breaker trips again. I did that all on shore power. As a test, I started the gen set, and tried switching to ship power. Everything works fine on ship power. Breakers all work. I do the same sequence for shore power again and it still doesn’t work, does the same thing. Uuuh, what do I do now? Is the switch that controls ship/off/shore power bad now or something?

[RGrew176]

There are a lot of really smart and experienced people here. Someone will be able to assist. Unfortunately I am not that person. My electrical knowledge is very limited.

[CptBacardi]

Hey, an easy fix for a change! I reseated the main 50 amp shore power cable and now it works. Go figure!!

[km1125]

The issue probably was with the "reverse polarity protection" part of the breaker. On generator, there's really no "hot" and "neutral" out of the generator.... you actually designate that when it's wired into something. On shore power, you have to live by what the power company has designated "hot" and "neutral". The breaker looks at the voltage differences between the hot, neutral and ground and it looked like the neutral had power, so it tripped the breaker.

You should make sure the connections on that cord and socket are clean and not corroded. You should also place a big load on there - run everything you can to try and get close to 50A load. Then feel the connector to see if it's warm at all. If it is, you have a poor connection somewhere inside and you need to fix that before it becomes a hazard.