RV "Hot Skin" and GFCI?

wa8yxm wrote:

tim.rohrer wrote:
So, especially for any electricians out there, what the heck happened? How could a pedestal be wired such that clearing a probably-blown GFCI (on a different circuit) could have led to this? And why didn’t the EMS system in my coach pick up the problem?

First that EMS. is it an INTELLETEC or a Progressive Industries.. Both companies use the letters EMS to describe two entierly different devices

Second.. IN theory there is no way a tripped GFCI can cause the symptoms you cite.. Now an OPEN GROUND.. that can do it but not a tripped GFCI. it is possibly the ground pin did not make good contact till the last time you plugged it in.

How can a open ground give you hot skin.

Well in a DC circuit we have a device called a resitive voltage divider..

ELectrically it looks like this

----/\/\/\/\---X----/\/\/\/\/--- THat is two resistors teh relative values determine the percentage of the voltage at "X" let's assume they are equal and since I"m tlaking DC we apply 12 volts to the divider, that means six votls at X

Now in A/C circuits we can replace those resistors with capacitors

---||----X---=-||----

Much easier to type.. This works, in A/C exactly as the resistive one did in DC.. apply 120 volts and X will be 60 assumign equal values for the capacitors


A capacitor is two pieces of metal with insulation between them

The Black wire, and the Green/Bare or the White wire and the Green/Bare

These form capacitors (low value but big enough if the wires are long enough, hundreds of feet is more than long enough) so they form a voltage divider.. The safety ground takes the GREEN/Bare wire to zero refernce (Ground) where the white wire lives. so you do not get hot skin.

It is a Progressive Industries EMS-HW50. I've sent the company an email asking why the device didn't detect the open ground. No reply yet.

For the past 24 hours or so, I've been leaning more towards the ground connection of the old shore power input having failed. Here is a question: Has anyone seen a situation where a damaged plug/cord was the source of the open ground AND the current leak? Conceptually it seems possible to me, although the damage leading the current leak would have to be on the RV side of the open ground, I would think.

For the rest of your post, I really had to dig into the recesses of my brain to pull up potential dividers :-) Truthfully, I'm probably a bit better with the theory than I am the application. In my case, I measured around 57V on the RV frame. Could I interpret this as indicating I've got worn insulation or a screw through a hot wire?

I've been researching ways to test for AC ground faults in the RV. It would seem that one quick way would be to recreate (in a controlled manner) an open ground situation and see if the hot skin returns. Then kill breakers in the RV until the voltage on the frame drops. Would this be a reasonable set of tests? On the other hand, the only way I can think of to create an open ground without cutting up my new cord is to remove the ground from the circuit breaker panel in the RV. I'm not interested in damaging other equipment so I'm not real crazy about this.

In the meantime, I'll continue the inspection method today and start opening junction boxes while inspecting all wires I can access.