50 Amp cable female end at trailer: what's going on?

[Jimibooks]

Hi, everyone:

Our 5th-wheel is currently parked near our house; and we had grandkids visiting, and they like to sleep out there, so I hooked the trailer up to a 30 Amp circuit installed set up specifically for this purpose, using an 30 Amp heavy-duty extension cord and 50 to 30A dogbone. The extension cable is plugged into its own 30 Amp circuit running to our 200 Amp main box in the house.

When I unhooked the shore cable from the trailer, the end looked like the picture shows. Uh, oh. The corresponding contact in the trailer that one plugs into is similarly blackened. Is this neutral? or ground? And: what's the likely cause, if this is enough information? Everything was working just fine, so far as I can tell.

Jim

 

[Redapple63]

That type of thing happens because of increased resistance and elevated temperature. I am willing to bet it is because of a potential loose connection or maybe a low voltage situation.

Remove the plug on both ends end ensure a good solid connection for all conductors at both ends.

Use a multimeter and check the voltage going in.

Lastly, these types of plugs do tend to spin a bit, even after you tighten that ring.

I would not plug that back in until you find the source of the issue.

Good Luck
Bill

 

[Hoopy Frood]

Personally, I don't think I would use that particular plug at all.

 

[Redapple63]

Personally, I don't think I would use that particular plug at all.

Good point. I agree, still think he should take the inside apart to ensure no loose connections on the inside and verify the voltage coming out of the sub box.

Bill

 

[Jomani]

I think you may have a bigger problem. That is the ground on the plug. It shouldn’t carry any current if everything is wired correctly. This is fairly common with either hot leg or neutral, but I haven’t personally seen it happen to the ground. I would check your supply outlet to make sure that it is wired correctly.

 

[DougW9876]

I’m with Jomani on this one. Burned like that means a loose connection that was arcing when electric current was flowing. A ground lug would only have current flowing if there is a fault in the wiring.

 

[LMagelitz]

Hi, everyone:

Our 5th-wheel is currently parked near our house; and we had grandkids visiting, and they like to sleep out there, so I hooked the trailer up to a 30 Amp circuit installed set up specifically for this purpose, using an 30 Amp heavy-duty extension cord and 50 to 30A dogbone. The extension cable is plugged into its own 30 Amp circuit running to our 200 Amp main box in the house.

When I unhooked the shore cable from the trailer, the end looked like the picture shows. Uh, oh. The corresponding contact in the trailer that one plugs into is similarly blackened. Is this neutral? or ground? And: what's the likely cause, if this is enough information? Everything was working just fine, so far as I can tell.

Jim

View attachment 46303

I’m also with [MENTION=49453]Jomani[/MENTION] …check the receptacle that the cord was plugged into.
Did you have any recent lightning incidents?

 

[jkwilson]

You likely have something going on with the ground and neutral in your trailer since you don’t mention tripping breakers. If ground and neutral are bonded inside the trailer, the ground wire could end up carrying 25A, and that contact isn’t designed for that kind of continuous current.

 

[Scott'n'Wendy]

A ground lug would only have current flowing if there is a fault in the wiring.

^^This^^^

Ground is your safety. Agree with Larry, look at the supply receptacle and see how it is wired.

 

[jkwilson]

^^This^^^

Ground is your safety. Agree with Larry, look at the supply receptacle and see how it is wired.

Absent a problem in the trailer, supply wiring issues won’t cause current to flow in the grounding conductor.

 

[LMagelitz]

Absent a problem in the trailer, supply wiring issues won’t cause current to flow in the grounding conductor.

Unless he has the hot in the equipment ground position, but then nothing would work in the trailer, so that can’t be it. Hard to say how much would flow in that case anyway, maybe/probably very little depending on all kinds of things. I’d say your thought of an errant N-G bond is the most likely.

 

[Redapple63]

He mentioned using a dog bone 50-30 amp. Perhaps the fault is in the dog bone.

Bill

 

[jkwilson]

He mentioned using a dog bone 50-30 amp. Perhaps the fault is in the dog bone.

Bill

I can’t think of a way that could happen. Ground can only have current flow if there is a ground fault occurs where current from the hot flows in the ground, or a neutral-ground bond. But current only flows in the grounding conductor under those circumstances between the fault/bond and the power source. So the fault is likely on the trailer side of the shore power connection.

Since OP has a fairly significant solar and battery installation, I’d put my money on an ATS problem, ATS mis-wiring or an unneeded neutral ground bond in the inverter setup.

 

[Tom Traveler]

I can’t think of a way that could happen. Ground can only have current flow if there is a ground fault occurs where current from the hot flows in the ground, or a neutral-ground bond. But current only flows in the grounding conductor under those circumstances between the fault/bond and the power source. So the fault is likely on the trailer side of the shore power connection.

Since OP has a fairly significant solar and battery installation, I’d put my money on an ATS problem, ATS mis-wiring or an unneeded neutral ground bond in the inverter setup.

i can think of a scenario where the problem could be in the supply outlet or dogbone. If something in the supply is making the ground lead to the trailer “hot”, current could flow to the trailer frame through the trailer ground lead, through the frame, through the jacks or stabilizers, and back to the supply at the main panel. This could only happen if the trailer frame is grounded somehow to earth. There might be enough resistance in this situation to keep the supply breaker from tripping.

I agree with jkwilson, however, that the most likely cause is a neutral/ground bond somewhere in the trailer. In either event, the OP’s trailer frame is “hot” and potentially dangerous. I wouldn’t plug the RV back in unitl you’ve diagnosed and fixed the problem. If you know your way around a voltmeter/resistance meter, you could start by seeing if the ground and neutral prongs on the RV’s power socket are connected. They shouldn’t be. If they are, you have a neutral/ground bond somewhere in the RV and you need to dig deeper.

I would also plug in just the dogbone, not the RV power cord, into your extension cord and, with the voltmeter, check the voltage between one of hot sockets and the ground socket in the female dogbone plug. It should be about 120v. If it isn’t, the problem is on the supply side.

If you aren’t knowledgeable about power issues and don’t have experience using a voltmeter, I would get a repair tech that is. A hot ground is a serious issue. Be very careful here.

 

[Jimibooks]

That type of thing happens because of increased resistance and elevated temperature. I am willing to bet it is because of a potential loose connection or maybe a low voltage situation.

Remove the plug on both ends end ensure a good solid connection for all conductors at both ends.

Use a multimeter and check the voltage going in.

Lastly, these types of plugs do tend to spin a bit, even after you tighten that ring.

I would not plug that back in until you find the source of the issue.

Good Luck
Bill

Thanks for this advice (as well as the "don't use this plug again." Right.

FWIW, voltage in and out of the cable, including the 30 Amp extension cable, is steady at ~121/122 Volts.

Continuity checks cleanly on all 4 lines, from end to end.

The trailer is currently getting its bearings repacked, so I can't examine the connector at the trailer itself, which (as I recall) is a bit blackened. So it, too, needs to be replaced.

The current cable is factory-supplied and molded at both ends; so it's really difficult to figure out if there's a poor connection interior to the plugs (on either end). There are 2 long screws on the female end, top and bottom in the picture I posted, but unscrewing them doesn't seem to make the "guts" removable, unless I just need to use more force.

The male end of the shore cable shows no evidence of overheating.

I'm considering getting the SmartPlug system from etrailer:

https://www.etrailer.com/RV-Power-Inlets/SmartPlug/SM76FR.html

Anyone familiar with how good this is (it should be very very good for the price!!).

But my main remaining question: the area that's blackened is the ground; correct? Why would the ground get hot unless there was a short involved? And wouldn't that kick a breaker?

Thanks for all the help. Further advice welcomed!

 

[Jimibooks]

Yikes! I should have read all of the further responses before posting my latest; sorry! I'll work on checking out issues at the trailer before proceeding, but that'll have to wait until I get it back from the bearing folks.

Thanks again!

 

[Jimibooks]

Tom Traveler said:

I would also plug in just the dogbone, not the RV power cord, into your extension cord and, with the voltmeter, check the voltage between one of hot sockets and the ground socket in the female dogbone plug. It should be about 120v. If it isn’t, the problem is on the supply side.

Yeah, I did this. It's at ~ 121/122v on either hot to ground on the dogbone. So the power supply seems OK.

 

[Tom Traveler]

I'm considering getting the SmartPlug system from etrailer:

https://www.etrailer.com/RV-Power-Inlets/SmartPlug/SM76FR.html

But my main remaining question: the area that's blackened is the ground; correct?

I think it’s been answered, but yes, that is the ground and, yes, there shouldn’t be any current flowing on that contact without a short or some bad wiring somewhere. If the RV power cord goes straight into the RV socket without a 90 degree adapter, the weight of the cord tends to pull that ground connection apart resulting in a poor connection. That may be why you had arcing from current that shouldn’t have been there in the first place. With regard to the supply breaker, there may be enough resistance in the faulty circuit, wherever that is, to prevent tripping the supply breaker. A neutral/ground bond in the RV would cause this without tripping the supply breaker.

The socket and plug from etrailer looks nice (it should at the price) except for one thing - why in the world didn’t they build it with a 90 degree angle at the plug so the heavy power cord hangs straight down from the RV socket instead of sticking out and putting a lot of strain on the socket?

 

[DougW9876]

Another thought i had on this, if the neutral and ground inside the trailer were reversed you would have voltage on the ground lug going back to the shore power source. This, along with all the other possibilities listed above means you have a bit of detective work to do to get this safely corrected.

When you tested the dogbone, with it plugged into a 30 amp 3 prong outlet you should have 120VAC on L1 to neutral and 120 VAC from L2 to neutral. You should also see 120VAC fro L1 to ground and 1200VAC from L2 to ground. Between neutral and ground should be 0VAC and between L1 and L2 you should see 0VAC. Also, just for test purposes, check the voltage in the 30 amp outlet where you should see 120VAC between L1 and Neutral and 120VAC between L1 and Ground with 0VAC between ground and neutral.

 

[jkwilson]

i can think of a scenario where the problem could be in the supply outlet or dogbone. If something in the supply is making the ground lead to the trailer “hot”, current could flow to the trailer frame through the trailer ground lead, through the frame, through the jacks or stabilizers, and back to the supply at the main panel. This could only happen if the trailer frame is grounded somehow to earth. There might be enough resistance in this situation to keep the supply breaker from tripping.

I wouldn’t argue with that being a possibility. I tend to make it lower likelihood, and think you do as well, because of likelihood and the odds that it would happen without another symptom. But I’ve found weirder things!