34v AC at Chassis Ground

[Dustdevil]

OK, here's one for the real experienced guys here.

2006 34SS Seneca.
Plugged in to 120ac shore power, 15 amps from the garage. So, only one side of the 50 amp circuit is active, or the 15 amps is split between both sides. When plugged in to shore power, I'm getting about 34 volts of AC power energizing all parts connected to the chassis. Trailer hitch, wheels, frame rails, etc all show 34 volts ac. When its unplugged from shore power, and the generator is running, there is no voltage apparent on the ground system. This last condition is normal. The former condition is not. Everything seems to work fine under both conditions.

I'm convinced it's not downstream of the AC power isolator that shuts down the genset if suddenly plugged into shore power, since all is OK with the umbilical unplugged from shore and the genset running. I'm convinced it's upstream. My suspicion is in the cord assembly, but I can't seem to get continuity between ground and either of the hot leads or the neutral in the cord itself. Even when plugged into the coach, and checking continuity at the opposite end.

SO, any of you experienced guys have any ideas? Just about to shove off tomorrow morning on a long trip. Not concerned about traveling or operating on the generator. Just worried what could happen when we plug in at our destination.

[Grumpy]

Originally Posted by Dustdevil

OK, here's one for the real experienced guys here.

2006 34SS Seneca.
Plugged in to 120ac shore power, 15 amps from the garage. So, only one side of the 50 amp circuit is active, or the 15 amps is split between both sides. When plugged in to shore power, I'm getting about 34 volts of AC power energizing all parts connected to the chassis. Trailer hitch, wheels, frame rails, etc all show 34 volts ac. When its unplugged from shore power, and the generator is running, there is no voltage apparent on the ground system. This last condition is normal. The former condition is not. Everything seems to work fine under both conditions.

I'm convinced it's not downstream of the AC power isolator that shuts down the genset if suddenly plugged into shore power, since all is OK with the umbilical unplugged from shore and the genset running. I'm convinced it's upstream. My suspicion is in the cord assembly, but I can't seem to get continuity between ground and either of the hot leads or the neutral in the cord itself. Even when plugged into the coach, and checking continuity at the opposite end.

SO, any of you experienced guys have any ideas? Just about to shove off tomorrow morning on a long trip. Not concerned about traveling or operating on the generator. Just worried what could happen when we plug in at our destination.

Bad cord is my guess, either at the twist lock or male end....It's 13 yrs old.

[Dustdevil]

That cord has been driven over a few times. It's entirely possible. My neighbor thinks it's a corroded chassis ground on the incoming AC power leads, but a different ground on the genset.

[SloPoke]

Originally Posted by Grumpy

Bad cord is my guess, either at the twist lock or male end....It's 13 yrs old.

Replace the cord... and then replace the 20 to 30 to 50 adapter. RE-TEST and post what you find.

[Grumpy]

Originally Posted by Dustdevil

That cord has been driven over a few times. It's entirely possible. My neighbor thinks it's a corroded chassis ground on the incoming AC power leads, but a different ground on the genset.

In other words if it was a good connection you'd get the full 110 on the chassis.... Not a good idea.

[Dustdevil]

Originally Posted by Grumpy

In other words if it was a good connection you'd get the full 110 on the chassis.... Not a good idea.

Oh, for sure it wouldn't be good.

[Dustdevil]

So, here's the latest. As I turn off the circuit breakers in my AC breaker box, the voltage apparent at ground begins to drop. The more breakers I turn off, the lower the voltage goes.

I want to test the 15 to 50 adapter. That's been dropped a few times in its approx 2 year lifetime, and the pins were bent once, then bent back. That could be it. Might be time to consider a main cord replacement also.

[Dustdevil]

Just took it all apart from the 115v extension cord to the 15amp to 50 amp adapter to the 50 amp shore power connector on the coach side wall. Tested everything while half-plugged-in, and all checks out fine. Checked each item down the line, except I can't check the 50 amp shore power connector without ripping all the wiring and insulation apart. Magically, it all suddenly works fine. WTH??

So, my suspicion, as SloPoke mentioned above, is that this is probably a bad 15 to 50 amp adapter. I never run anything high power on that, but it's good for operating a tv or a vacuum cleaner when we return from trips. I still don't quite get why the voltage would drop when turning off a few breakers, but I'd have to draw out the probable circuit to understand that one.

Thanks for the advice, and I'll keep you all posted on what I find as we cruise up to our destination and plug in there.

[SloPoke]

Originally Posted by Dustdevil

Just took it all apart from the 115v extension cord to the 15amp to 50 amp adapter to the 50 amp shore power connector on the coach side wall. Tested everything while half-plugged-in, and all checks out fine. Checked each item down the line, except I can't check the 50 amp shore power connector without ripping all the wiring and insulation apart. Magically, it all suddenly works fine. WTH??

So, my suspicion, as SloPoke mentioned above, is that this is probably a bad 15 to 50 amp adapter. I never run anything high power on that, but it's good for operating a tv or a vacuum cleaner when we return from trips. I still don't quite get why the voltage would drop when turning off a few breakers, but I'd have to draw out the probable circuit to understand that one.

Thanks for the advice, and I'll keep you all posted on what I find as we cruise up to our destination and plug in there.

Without having that adapter in my hands to test... with a meter - I suspect that the neutral on the adapter is open(or bad) Next steps are test EVERY outlet in the motorhome with a voltmeter, then turn one of the AC units on fan - and re-test. Then the other AC unit on fan with the first one off - and re-measure. If you want to call - IM' me and I will give you my number.

[jd99336]

I am very confused by this thread, so hopefully some of you electrical wizards can clarify.

1) If you are plugging into your garage at a 15 amp plug in this is normally a 110v circuit. A 50 amp RV plug is really just two 110v circuits going to different places (one powers house/micro/front AC for instance and second goes to aft AC). Changing all the adapters and plugs in the world will still only result in one side being energized....right??? Or maybe the Senecas are different than Class A's I have owned in the past.

2) Why would you expect ANY voltage to the chassis ground other than 13-14v. 34v is weird and your 110v should NOT ground to the chassis (keep your fire extinguisher handy) as that is a closed electrical circuit to the neutral in your 110v box.

Again, I am in the middle of a work project, so maybe I am not understanding this, so ignore me if I am out of line.

[Robbbyr]

Originally Posted by jd99336

I am very confused by this thread, so hopefully some of you electrical wizards can clarify.

1) If you are plugging into your garage at a 15 amp plug in this is normally a 110v circuit. A 50 amp RV plug is really just two 110v circuits going to different places (one powers house/micro/front AC for instance and second goes to aft AC). Changing all the adapters and plugs in the world will still only result in one side being energized....right??? Or maybe the Senecas are different than Class A's I have owned in the past.

2) Why would you expect ANY voltage to the chassis ground other than 13-14v. 34v is weird and your 110v should NOT ground to the chassis (keep your fire extinguisher handy) as that is a closed electrical circuit to the neutral in your 110v box.

Again, I am in the middle of a work project, so maybe I am not understanding this, so ignore me if I am out of line.

My 50 amp to 30 amp adapter just takes the one "hot" lead supplied by a 30 amp outlet and connects it to both hot leads of my 50 amp plug. And obviously if I connect my 30 amp adapter to my 20/15 amp adapter it is still only one hot lead being sent to both sides of my electrical panel. My EMS display shows identical voltage on both legs whereas when I am connected to an actual 50 amp outlet it isn't unusual to see a couple of volts difference between legs, especially if I have something drawing just on one of the legs.

[Harvard]

IF you are measuring an AC Voltage from Chassis to Earth it is because your RV has an Open Ground Conductor.

In other words, the RV ground conductor is not making contact with the shore power pedestal ground.

With an open ground the RV Chassis will float above Earth in proportion to the HOT to CHASSIS and CHASSIS to NEUTRAL stray capacitance.