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30 amp power cord problem


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#1 Lmar1

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Posted 12 March 2012 - 07:17 PM

I need some electrical advice. The 30 amp power cord (2000 Rexhall Anthem) was very hot and soft when I went to unplug from a site at Nellis AFB. The park plug-in seemed loose and hot when I unhooked and my cord smelled like burning rubber. I had a new 30 amp power cord installed at The Hitching Post in Las Vegas. The motor home has been plugged in at numerous other Parks since with no problems. I have also had it plugged in to the 15 amp outlet on my Honda 2000I generator, with a 30 to 15 adapter and had no problems. When we returned home I plugged into my garage outlet with a 30 to 15 adapter and it popped the garage ground fault breaker. It does the same at my neighbors plug in. I've replaced the adapter and it still does it. Plugged it back in the Honda generator and it works fine. Could they have crossed the wires (white to black) when they put the new cord on? Would that cause the ground fault breaker to pop? Any thing else to I could check?
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#2 AFChap

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Posted 12 March 2012 - 07:30 PM

It is very common for modern coaches to trip a gfci when you plug into a residence. Normally, I have found that I can then reset the gfci and it works fine. Occasionally I will find one that simply will not work with an RV. I believe that reversed hot/common could cause a modern gfci to trip, but I would try simply resetting or using another outlet/circuit long before going there.

The hot/melted 30a cord/plug most often is the result of an outlet and/or male plug in poor condition. Team that up with heavy use close to 30a, and you get overheated cords/outlets/connectors.
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#3 Chuck & Elva

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Posted 13 March 2012 - 05:21 PM

Lyndal,

Worn and loose receptacle contacts result in a loose plug. Loose metal-to-metal contacts result in higher resistance which results in increased heating effect. For both the contacts and the surrounding vinyl covering of the power cable.

I have a 50 amp input on my coach and never have tripped a 15/20 amp GFI. The constant GFI tripping is due to a current leak to ground somewhere in your RV. It is a violation of code because it can be dangerous. This is the very reason GFI's were developed. A good tech can measure the leakage and find the source.

The Honda (and all portable generators) has a "derived ground" which means it is not connected to "earth ground" as is the case with the electrical outlets. If you put an in line GFR device in the cable to your RV you would find it trip also.

Open the box on your rig where the power cable goes into. The black wire should go to a circuit breaker. The white wire should go to a bus bar with several screw attachments. The green wire should go to the case. If your RV does not have an "input breaker" like mine originally did not, and goes directly to transfer switch, it becomes more difficult for non-electrical folks to trace things out.

Edited by Chuck & Elva, 13 March 2012 - 05:29 PM.

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#4 Lmar1

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Posted 13 March 2012 - 06:16 PM

Thanks for the quick response. I really know nothing about 110 electrical circuits. I can troubleshoot DC systems because of my USAF background. As soon as the Washington winter rains stop here in Bellingham I'll follow your advice and open the box. Everything is easy to get to, even the auto transfer switch. Never experenced GFI tripping before they replaced the cord on the m/h. One of my neighbors suggested that I just cut the ground prong off the 30 to 15 adapter. He had the same problem on his m/h and techs couldn't find anything wrong so that was his fix. I haave enough fear of 110 volts to try that.

Lyndal,

Worn and loose receptacle contacts result in a loose plug. Loose metal-to-metal contacts result in higher resistance which results in increased heating effect. For both the contacts and the surrounding vinyl covering of the power cable.

I have a 50 amp input on my coach and never have tripped a 15/20 amp GFI. The constant GFI tripping is due to a current leak to ground somewhere in your RV. It is a violation of code because it can be dangerous. This is the very reason GFI's were developed. A good tech can measure the leakage and find the source.

The Honda (and all portable generators) has a "derived ground" which means it is not connected to "earth ground" as is the case with the electrical outlets. If you put an in line GFR device in the cable to your RV you would find it trip also.

Open the box on your rig where the power cable goes into. The black wire should go to a circuit breaker. The white wire should go to a bus bar with several screw attachments. The green wire should go to the case. If your RV does not have an "input breaker" like mine originally did not, and goes directly to transfer switch, it becomes more difficult for non-electrical folks to trace things out.


Lyndal (Lyn) Glenda Marohl

#5 docj

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Posted 13 March 2012 - 07:03 PM

One of my neighbors suggested that I just cut the ground prong off the 30 to 15 adapter. He had the same problem on his m/h and techs couldn't find anything wrong so that was his fix. I haave enough fear of 110 volts to try that.


Your neighbor's advice belongs up there with taking batteries out of smoke detectors when they start to chirp because they are getting too old and checking for gas leaks with a flame!

Irrespective of GFCI issues, cutting off ground prongs on plugs is an excellent way to end up with a very bad shock or electrical burn some day. The ground is your safety "lifeline"; it's there for a very real reason.

If you never had this problem before you had the new power cord installed then my guess is that they did a slopped installation and that there is a whisker of a strand of copper wire bridging the terminal block where the cable is terminated. The wire might not even be touching the terminal, but might be just close enough for a small current to flow down that path. GCFI's are exceedingly sensitive to ground current flows of even microamps. If there is no problem at the terminal block then there is an internal crack in the molded plug which is letting some current flow.

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#6 Kirk

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Posted 13 March 2012 - 07:07 PM

You are wise to be reluctant in removing the ground pin from the plug.

It may be that the tech who installed the new power cord connected the ground and the neutral together inside of the RV distribution box. If so is wrong as the two should not be bonded inside of the RV.

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#7 Lou Schneider

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Posted 13 March 2012 - 07:51 PM

Kirk's right. GFCI's trip when the current going out the hot line does not precisely match the current returning on the neutral. The assumption is the extra current is leaking to ground somewhere, maybe through a person.

If ground and neutral are cross-connected inside the RV, part of the neutral current returns on the ground wire. Since the current returning through the neutral line no longer matches the hot current coming out of the outlet, the GFCI trips.

If removing the ground pin (or using a 3 to 2 wire adapter) solves the problem, it only confirms that ground and neutral are cross-connected somewhere. By breaking the ground lead you force 100% of the current to return through the neutral line and the GFCI is happy.

Another way to tell if ground and neutral are cross-connected is to measure between the ground and neutral pins on your power cord. There should be infinite resistance between them. If you measure any resistance at all, you have a G-N short.
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#8 Stanley P. Miller

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Posted 13 March 2012 - 09:29 PM

If you do cut the ground make sure you check to see if the rig will knock you over when you touch it. Yes it will hurt like the dickens and does have the possibility of killing you but far better that than zapping the wife, kid or grandkid. 110 volts kills people on a regular basis, it can't be taken for granted.

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#9 Dutch_12078

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Posted 13 March 2012 - 09:30 PM

One thing that hasn't been mentioned, once you get the GFCI issue sorted out, pick up a 50 amp male to 30 amp female adapter at an RV shop or even some Walmart stores. It's not that uncommon to find badly worn 30 amp outlets at campgrounds that wont hold your plug tightly, and using the adapter can save you from frying another cord.

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#10 RV

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Posted 13 March 2012 - 11:07 PM

My routine when hooking up to a new to me power pedestal was to take my outlet tester and test the pedestal outlets to be sure it had all the regular connections right. It is a simple 110 wall outlet tester with three lights. I use a 110 adapter three prong with it to 30 amp, and for 50 amp one further dogbone adapter. even thought that will only test one leg of the two hots on a 50 amp four prong two 110 leg connection. Once I was sure of the power and grounds I would turn off the breakers and first run my 30 or 50 amp plug in and out of the receptacle all the way in and out fast about ten times to friction off some of the oxidation from the inside contacts in the receptacle, which is what causes the resistance that results in heat and melts your plug ends. You can fix it but if you don't the first time it gets hot enough to damage that molded end the insulation is degraded inside and it will get worse until the whole cord is bad. To fix it remove the old plug and strip the insulation away and strip the insulation on the wires inside. Keep stripping back until you get to good insulation that isn't heat damaged, it is obvious. Once you see how far the damaged insulation from heat went then go one more foot and cut the cord completely and discard all of the end. Install the new cable ends, both male and female, making sure of the connections and tightness. Then make it a habit to use the plug itself as a friction cleaner with a few insertions and removals after testing the wiring. I burned two expensive cables until i learned. Sure all the other things contribute or cause similar results, but never run any power cord/cable with no ground. And I guarantee you that you will melt fewer plug ends doing as I outlined. But only after checking the outlets. That usually takes care of the other things to the extent you can easily test in the field without an electrical background.
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Hope that helps.

Edited by RV, 14 March 2012 - 03:51 PM.

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#11 weldon

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Posted 14 March 2012 - 01:37 AM

I am with RV, last year we were in a CG & the 50 amp plug only had on good leg ( or side) that would not hurt anyone, but just goes to show you have to check it yourself.
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#12 Chuck & Elva

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Posted 14 March 2012 - 07:54 AM

I would avoid any advice from that neighbor again. Also, use a multimeter to test for current on the chassis. The "touch test" went out with the Edsel.

For general information for inquisitive minds, the early GFR's of the '70s would trip at 2 to 3 milliamps. I measured them. This resulted in much nuisance tripping due to line induction and other factors. The last group I tested was in the '90s and they tripped at 8 to 10 milliamps, which is .008 amperes. Now that isn't much, but keep in mind your heart can go into fibrillation at 30 to 35 milliamps. If that is not corrected relatively quickly, you will die.
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