Circuit Breaker Surprise

[Juliet 15]

Hi all! We have a 58 LRC from 1975 that has thrown us for a loop. :^/

1. Yesterday all the AC power dropped off. I checked the big AS panel at the helm and discovered the bottom right "Hatteras 120VAC Lines B and C" breaker had flipped.
2. This is a big black 4-pole breaker sitting next to 2 white breakers.
3. The white breakers are marked "FAULT" and "OVERVOLTAGE" respectively.
4. After much investigation (read: 8 hrs of laborious troubleshooting) I've determined that the white "FAULT" breaker is tripping first, causing the black 4-pole breaker to follow suit.
5. I disassembled ad examined all of the bow and stern shore power hookups - all is in order; no shorting, no burn marks, no loose wires.
6. I opened up the big AC panel and examined the back side - all is well, nothing shorting, no burn marks, no out of place wires.
7. I shut off all other AC circuit breakers in the entire boat to isolate individual systems. No change.
6. I used shore power - no change. As soon as power is applied, the white breaker trips followed instantly by the black 4-pole Lines B and C breaker.
7. I tried going off generator power - no change.
8. I tried swapping a different white "FAULT" breaker from another part of the panel. No change!
9 (Here's where it gets interesting) I decided to try leaving the "FAULT" breaker disconnected.
a. I disconnected the "IN" wire to the white breaker.
b. I flipped the black 4-pole breaker back on.
c. I started the genset - and everything worked!!
d. I shut id own and connected to shore power - and it worked.
10. As long as I leave the white beaker disconnected all the AC system work normally.

I left it on for long enough to charge the batteries, then shut it off. Anyone have ideas as to what is wrong or where to begin looking? Similar experiences?

Thanks for any insight!

[Cricket]

Think my first try would be to find/purchase and install a new fault breaker.
Breakers do go bad and also GFCI outlets, hopefully it's as simple as that.

[Juliet 15]

Yeah, I thot so too, but I swapped circuit breakers and the problem stayed with the location. It didn't move. Can't be the breaker.

[SEVEN]

All the breakers are old they may be weak. Install a brand new one hopefully that will resolve your issues.

[Boatsb]

I've been using the new elci breakers on upgrades. 50 amps in a package that has reversed polarity indicators , power lights and all the necessary safety features. I'd put that at the inlet (no more fuses to deal with) and then all you need at the main panel is the legs and neutrals.

[sixty]

I've been using the new elci breakers on upgrades. 50 amps in a package that has reversed polarity indicators , power lights and all the necessary safety features. I'd put that at the inlet (no more fuses to deal with) and then all you need at the main panel is the legs and neutrals.

Do you have a specific part number you use? I would love to ditch my fuses.