Strange(?) Electrical Issue. Power my AS trailer off of my AS Interstate

[kaylorsan]

Issues such as this caused be to quit my electrical engineering education and switch to mechanical engineering...

I received delivery of a 1969 AS Sovereign trailer the other day. It is currently sitting on a plot of land without available shore power. It has a 30 AMP voltage center installed (Parallax Power Supply 5300 series power converter) with a standard round 30AMP type plug input.

I can power it with no problem off of a portable generator. I have an adaptor that I use to convert the 30AMP round plug to a standard 15AMP plug. I plug it into the generator and everything works well.

I use the same setup to plug my Airstream Interstate into 15AMP shore power when I'm at home.

Seeing that I don't want to constantly run the generator to power the trailer, I figured that I would try to power it from my Interstate (I have a fair amount of battery storage and a rocking solar system). When I initially plugged the cord into the Interstate outlet, I immediately tripped the Interstate's GFCI outlet. I figured the trailer load was too high, so I shut everything down in the trailer and tried it again. Same result. I thought maybe it was a wiring issue with the trailer, so I just plugged in the 15AMP side with the 30AMP side disconnected. Same thing. The GFCI trips immediately without any load present. Seems like it is wiring issue, however the wire setup works fine when powered by the generator.

Being that it was dark and cold while I was doing this, I just fired up the generator and plugged into it without issue. We left the next day and I didn't get a chance to troubleshoot any further.

The Airstream has a Magnum MMS1012 inverter and runs all of the AC in the Interstate without issue.

My guess is that the problem has to do something with the power cord or 30-15AMP adapter. Something that the generator doesn't mind, but the GFIC is sensitive to.

I head back down this weekend with the Interstate and will trouble shoot some more. In the meantime, anyone have any suggestions?

Thanks,

- Kaylorsan

[J. Morgan]

My off the cuff guess is that the line and the neutral are crossed in the trailer plug, if your generator neutral is un-bonded, as many are, then the generator wont care, where your interstate, if the neutral is bonded to ground may care.


Brevi tempore!

[idroba]

GFCI's can drive you crazy with their incompatibility with certain equipment. It only takes .005 amps (5 mA) going where they think it should not to cause them to trip.

Although I hesitate to suggest this, can you plug into a non GFIC outlet and see what happens? I don't know how the Magnum inverter in the Interstate works, is the entire output GFCI protected so that is not an option?

Lewster might have some insight into the issue, he knows Magnum inverters very well. Lets see if he chimes in here.

[J. Morgan]

Fwiw, if the line and neutral are swapped in your trailer plug it is a serious hazard when plugged into shore power.


Brevi tempore!

[Nuvite-F]

Originally Posted by idroba

GFCI's can drive you crazy with their incompatibility with certain equipment. It only takes .005 amps (5 mA) going where they think it should not to cause them to trip.

What Idroba said. 30 Amp trailer outlets do not contain GFCIs because certain loads may have enough current leakage to ground to trip them. Some common culprits are electric heating elements (refrigerator, water heater), wet connections (outside outlets or inside switches and outlets if the shell is leaking) and converters (RFI filters on the 120 Volt input).

By all means check for proper connection of hot, neutral, and safety ground wires in the trailer, but if they are all OK you will need to start looking for leakage paths. Might try a VOM on high resistance range (with power disconnected from the trailer!) A "megger" (high voltage insulation tester) might come in handy. This kind of problem is often tough to find.

[Protagonist]

Turn off any GFCI breakers in the trailer, and it should work fine.

If you're plugging into one of the Interstate's external outlets on the passenger-side quarter panel, it's a GFCI outlet (being outdoors where it can get wet, it has to be). Having two GFCIs in series typically causes the one further "upstream" to trip, because the same circuitry that allows a GFCI to detect as ground fault reads AS a ground fault when plugged into another GFCI.

We used to see the same thing all the time on construction sites when I was still working for a living; it took us ages to figure out the source of "nuisance trips" like these, but once we learned not to have two GFCIs in series, the problem went away.