1979 FC GFI issue

[Conmega]

So I've seen discussion of the known GFI issue on BBs mostly on 80s PTs and a few 80s FCs but nothing much on 70s FCs from what I could find in the searches, maybe I used the wrong keywords.

We have one external 30A connection that my parent's RV currently uses. I just wanted to get mine attached to keep the batteries charged up and so my bus came with two 30A cables with adapters down to standard 15/20A household plugs. I went to attach one of those and of-course the GFI blew.
I haven't tried the 50A since I don't believe I have the cable for it. I have not searched through all the lockers yet. I just found an extra Alternator??? in one of my lockers the other day so random things still to be found.

From what I was reading the GFI blows because of the reverse polarity lights present across neutral and ground. So I cut these out of the circuit for now...
Still blew. I switched off all breakers in the bathroom closet, switched the main off, gen, 50A, 30A switch to off plugged it back in, no blow.
Switched the main switch to 30A, switched on the 30A and 50A "Main" breaker in my breaker panel. Still ok.
Started going through the breakers, hot water heaters were off because its winterized, but went through the rest of them and it blew the GFI on the battery charger.
Everything else was OK.
Saw I had no power in the kitchen area, figured that both 30A plugs are required to power the entire breaker panel, 120V interlaced in the middle of the panel so that if you had 240v service you could theoretically get 240v from a dual breaker.
Tried turning on the central vac, heard the motor spin about a half turn then blew the GFI.

So it seems the polarity lights in mine aren't the only issue. Any current draw causes the GFI to blow.
It may be me drawing a little too much current over a 100FT extension cord, But I wouldn't expect the GFI to blow, more so the cable to catch fire or the breaker in the house to blow...

Unfortunately the only non-GFI socket is the 30A my parent's RV uses.
So for now I have an external battery charger on the batteries to keep them topped off.

Discussion, thoughts?

[isp2952]

Connor, I don't know how your bus is set up, but if it is like mine, try this. My chargers were not hardwired to the coach. Most of the buses of my vintage are set up the same way. The charger just plugs into a 120v duplex outlet in the charging bay. Unplug it and plug the charger directly into a cord of a 120v duplex outlet in the garage or whatever you have available. Hopefully this helps. If yours is hard wired, then my solution is of no use to you.

[Camper Dave]

Connor there are a few issues at play here.

1) GFCI's go bad, I have seen them go bad within a few days when constantly tripped. It is best to replace them if you are having any doubt, a quality GFCI will cost around $15

2) The voltage drop on a 100ft cord will be minimal for MINOR loads. Do not overload the house/garage, try to keep it within 80% of the 15/20amp breaker. If you have a coach load gauge up front (that is accurate) that may help.

3) Some older battery chargers create an IN-RUSH current that will easily trip a 20amp breaker or old and weak GFCI (GFCI is NOT and over current device). This will definitely take place if batteries are low. The same applies to AC's and fan.

3) check the data plate on the charger for amperage draw

hope this gave some insight

[MRPutz]

I'm a little confused about your "tripping" breaker? Is it tripping on current or GFI? These are two different events. GFI just means is sensed current flow from common to ground. If it's tripping due to that it could also be the source is not wired properly!

As stated GFI's do go bad also.. If you have narrowed it down to the charger is it a smart charger or old battery boiler? The smart charger can be programmed "down" for a smaller breaker size. This is assuming of course it's an amperage issue and not a GFI one.

So what gauge wire is this 100' extension cord using? Do you know the current draw from the bus side? We can calculate voltage drop.

[Conmega]

Micheal: Always trip the GFI, not a current trip.

Dave: Hoping its a bad GFI. Since when any load, like the central vac which is a few hundred watts I believe, blew the GFI.
I have to find my battery charger, it appears to be in the rear left compartment.

Unfortunately it looks like the charger is wired in permanently so I can't just plug in.

I am going to try and plug into the 30A my parents RV plugs into at some point since its non-GFI.

[Gene Mehr]

My fc trips the gfi at some places but not at home. I turned off all brackers in the bus. But not the mains. Turned on one breaker to time until blue the GFI in my case the fridge is what is the culprit so I took the fridge up with a separate cord and was okay