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Old 12-26-2015, 01:37 AM   #1
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Thumbs down Tripping Breakers

The 110 in our DIY is straightforward. Three AC outlets toggle between shore power and invertor. The inlet on the bumper is marine-grade. Everything works fine at home, even plugged into a notoriously sensitive GFI.

We have not yet been successful using shore power at a campground--we have tried 5 sites in two campgrounds. Breakers flip instantly.

Suggestions where to look for the problem?
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Old 12-26-2015, 01:40 AM   #2
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The 110 in our DIY is straightforward. Three AC outlets toggle between shore power and invertor. The inlet on the bumper is marine-grade. Everything works fine at home, even plugged into a notoriously sensitive GFI.

We have not yet been successful using shore power at a campground--we have tried 5 sites in two campgrounds. Breakers flip instantly.

Suggestions where to look for the problem?

Are you plugging into the 15 amp or 30 amp outlets? GFCI? Which breakers trip? What inverter?
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Old 12-26-2015, 11:39 AM   #3
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15-amp

3 Breaker w/built-in GFI
2 Breaker w/separate GFI

All 5 tripped.

Invertor is a 750W HF.
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Old 12-26-2015, 12:05 PM   #4
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There was an interesting topic on the RT Yahoo Group - https://groups.yahoo.com/neo/groups/.../topics/107607 - that might give some ideas.

It sounds like your setup is like an extension cord. The odd item would be the inverter so I'd look at how you are breaking the connection to it when plugging into campground power.

I'm guessing that the breakers that are tripping are at the campground pedestal.

I can measure resistance between ground and neutral, hot and neutral and also hot and ground on a really inexpensive 1000W modified sine wave (MSW) inverter that is sitting unused on my work bench. The exact same tests on a 1000W pure sine wave (PSW) inverter sitting unused right next to it shows no continuity at all between ground and neutral, hot and neutral or hot and ground. No continuity is good in this example.

A circuit tester is handy for checking reverse polarity etc., both at home and in the van. You can even use it to check 30amp RV outlets using an adapter.

circuit tester.JPG

circuit tester 30 amp RV outlet.JPG
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Old 12-26-2015, 12:30 PM   #5
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I should add that I've used the PSW inverter in the van on an automatic transfer switch. I would not use the MSW inverter in the van on that same switch. I'd expect something to trip if lucky or smoke to come out if unlucky.

I'd use the MSW inverter in the van only if it was completely separated from the AC wiring in the van when plugged into sure power.
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Old 12-26-2015, 12:39 PM   #6
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Is there a way to access that info without joining yahoo?
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Old 12-26-2015, 12:52 PM   #7
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No, you'd have to join the group.

It was a discussion on how to wire in a MSW inverter. It got into the difference between how you end up with 110V from a MSW and a PSW inverter.

I think the conclusion was to use a 3 Pole Double Throw switch if the OP used a manual switch. That would completely separate the MSW inverter from the coach AC wiring when plugged in campground power. He hadn't purchased the inverter yet so hadn't put a meter on it to test.
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Old 12-26-2015, 03:03 PM   #8
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As Marko has mentioned, make sure the outlets are wired correctly with a circuit tester. You should always also check the campground outlets, they are incorrect all too often.

How many of the leads are you switching with the selector switch? If the inverter has the neutral and ground bonded, which it might or might not, you can wind up with them bonded two places once you hook up shore power, if you are just switching the hot, which is not good. The Harbor Freight inverter probably has plenty of leakage through it to trip GFCI breakers, like the cheap inverter Marko tested, if all three legs aren't switched.

First step would be to do the campground test with the inverter completely disconnected to see what happens. If that fixes it, I would do the three pole switch to switch all the lines together, with a center off for timing.

Some other points, you should have a switch on the inverter 12v side to shut it off, so you don't have a hot swap or be using power all the time when on shore power or not using the AC on inverter. You also don't want any significant loads on the inverter when you turn it on.

One thing to remember about vehicles with inverters, or generators for that matter, is that you have no earth ground like you do at home or when on shore power. That means that all AC in the van can be floating without that reference. In an extreme example, you could have 215 volts on the hot and 100 volts on the neutral (and maybe ground) and the system would work just fine. The danger comes when you get a short of some other issue (or if the neutral and ground are bonded) and that 100 volts gets to the chassis of the van. If you get between the chassis and the earth you can get zapped. Add to this that some inverters, usually the low end MSW ones, do this on purpose, putting 1/2 the voltage as a + on the hot 1/2 the voltage as a - on the neutral.

IMO, there is probably no way to make an inverter or generator in the van 100% safe, as there will always be something that could happen to put voltage on the chassis, but you can reduce the risk to very low levels. It is hard to get things really safe, when you have no idea how the inverter is wired internally or how much leakage it has.
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Old 12-26-2015, 11:03 PM   #9
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Thanks, Guys. I have forwarded the info to my "resident electrician" who keeps me warm at night. I will let you know how it develops.
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Old 12-31-2015, 03:32 PM   #10
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More info:

Inverter is putting out only 95 volts.

Inverter is not grounded.

The GFI trips even with inverter is unplugged.

An extension cord with 0.1 ohm difference between neutral and ground can trip the GFI even when the shore power breaker is off. I routinely use this same cord in the same outlet for power tools.
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