GFCI

Have you also checked the 20A outlet source with your circuit tester before you have plugged in the trailer Shore Power cable or RV30A to 15A long adapter.... You want to see the two bottom lights burning for CORRECT from the source 120VAC as shown in this photo...

Google Image

Most of the time the GFCI is tripped because of a bad ground wire on the source connection in your House/Garage 120VAC connection.

Also the RV30A to 15A long adapter may be at fault with its ground pass through. If you are using an extension cord plugged into the 120V outlet before using the RV30A to 15A Long Adapter and your Shore power cable you need to check the extension cord as well with the circuit tester.

Anything you plug into between the 120VAC source connection could be at fault before you plug-in the trailer Shore Power cable connector which could trip the GFCI breaker.

Roy Ken

Yes, I have tested the source outlet with that same circuit tester and the two bottom yellow lights lit up verifying the outlet is wired correctly.

If I leave the microwave circuit breaker off, it does not trip.

Have you unplugged the micro? It can cause a ground fault.
A standard breaker isn't able to create a ground fault by itself.

Use an extension cord to connect the MW to your GFCI outside plug. Results?

Yes, I have unplugged the microwave and it still trips.

If the outlet is wired correctly and the circuit breaker cannot cause the fault, that leaves the wiring. The kitchen is on a slide if that adds any clues??

My microwave has an extension 120VAC circuit receptacle located at the top of my cabinet where the microwave is plugged into it...

You could unplug the microwave here and then plug your circuit tester into this 120VAC source and see what it reads... Might have a bad connection back to the trailer 120VAC Distribution center...

All of the grounds inside the trailer all routed to the 120VAC Power Distribution center and passed through back to the 120VAC ground wire from the source. This line is also going to frame ground on the trailer. The NEUTRAL Wire for all receptacle gets routed back to a terminal strip and is isolated from from the trailer ground and passes through to the shore power Neutral connection. The Circuit breakers are only in the HOT wire loop between the shore power HOT wire connection and each of the 120VAC HOT connection at the receptacles. I guess all of this makes sense haha...

This pictorial kinda shows what i am saying here...

Google Image

Roy Ken

The slide would definitely be suspect haha... all those cables move back and forth with the slide... You should be able to check the wiring for being frayed or something...

Plugging in the tester where the microwave plugs in will show an open ground perhaps... Maybe you have said that already haha...

Roy Ken

This is where I am stuck in solving this issue

- microwave is unplugged
- outlet tests no problems ( wired correctly, no open grounds)
- I have isolated it to this circuit ( no faults for 48 hours with this circuit turned off at the circuit breaker)
- house outlet tests no problems
- wouldn't be the extension cord, 50/30/15 adapters as it is working with microwave circuit turned off.

Thanks for all the help so far

Remove the receptacle and look for a small hang nail of wire making contact between the neutral and ground.

If there is any, Disconnect the power, black wire from receptacle to see if issue goes away.

Is it possible to plug a different MICROWAVE unit into this plug and see what it does... I had a microwave unit that for some reason really tasked the 120VAC line. It worked just fine but sometimes it trip the breaker and also made a louder sound when operating than similar microwave units would. Somehow it modulated the 120VAC line differently so to speak when being used...

We all are just plugging away with things to check - glad you taking it all in... Hard to troubleshoot things without actually being there haha...

If the tester is not showing any faults with your 120VAC receptacle where the microwave plugs into it then I would go with the circuit tester. Perhaps something is weird about the microwave unit... You are definitely doing the things I would be doing tracking down the problem...

Have you ever seen the microwave work before using a regular RV 30AMP Pedestal type connection...

I know my microwave in my 5th wheel is also an convection oven combo which I have never used that part of it... It really sounds weird when running in convection mode...

In my off-road POPUP trailer which is what I only camp in now I have used both a high wattage and low wattage manual type microwave units without any 120VAC problems... When camping off-grid I use the low wattage white faced microwave with spring loaded dial-up timer hehe... It draws around 600 watts... I only use it for heating up my coffee and doing a 5-minute baked potato wrapped in cellophane to go with my steaks on the grill...

Roy Ken