Last month I published Part 1 of RV Hot-Skin testing. Here's Part 2 which takes a deep dive into hot-skin troubleshooting! Please proceed with caution since this can be dangerous….
I would agree, but I’m going to test this anyways. I have a 4-wire Kelvin Bridge ohmmeter which can test down to 0.001 ohms and self-calibrates to null out the lead resistance. I’ll take pictures.
Mike, On my 1994 Prowler 25P I am reading 12V at the frame. When unplugged from shore power and I run a ohms test from the ground to the frame it is OL. is this as simple as just replacing the 30A cord?
It does sound like you’ve lost continuity of the ground wire in your shore power cord to the RV chassis. However it’s possibly that there’s a break in the ground conductor between your twist-lock inlet connector and the chassis grounding lug.
Great info Mike. If you could create a PDF of all three parts people could download them and make printed copies if need be. I've always kept a information file on any vehicle I have owned. TSB's, shared tech info through groups like this one. Thanks
Good stuff Mike, but who among us out here is actually going to do all this? I do the hot skin test sometimes but that's it. I plug my tester into the pedestal to make sure the connections look good before I plug the trailer in, and that's it.
This test procedure is for troubleshooting the cause of a known hot-skin condition. I get emails all the time from RV owners with their trailers stuck in a repair shop, and the RV technicians can’t determine the cause of a hot-skin shock. It’s actually pretty simple when you understand the basics.
Wait until I publish part 3 which includes all the various current leakage sources.
Showing the test to the stabilizer jack screw is not a good place to test. The jack screw itself is not bonded directly to the trailer frame. It passes though the threads to the nut and then through the pivot pins on the legs. All of these are high resistance connections.
Bob, I would tend to disagree. There might be a few milli-ohms of added resistance through the jack screw, but I wouldn’t call it a high resistance connection that could affect the test results.
However, your point is important. For this test you need to probe an unpainted, non-corroded metal spot on the RV that’s directly connected to the chassis. That can be a challenge to find on an older RV.
Interestingly, I used to perform this test on a wheel lug nut, but then I discovered that my trailer axle was mounted in rubber, so there was an extra 40 ohms of resistance from the wheel lug nut to the frame itself.
I still disagree. All the mechanical points on the screw jack may be greasy, insulated, or rusty, pivot points. Just wiggle the stabilizer, every point of contact moves.
My trailers is in storage right now. But you will have to agree that a moving moving mechanical connection is a poor way to test conductivity. Not much different than using the ball and coupler on a trailer as a substitute for a hard wired ground connection.
I would agree, but I’m going to test this anyways. I have a 4-wire Kelvin Bridge ohmmeter which can test down to 0.001 ohms and self-calibrates to null out the lead resistance. I’ll take pictures.
Mike, On my 1994 Prowler 25P I am reading 12V at the frame. When unplugged from shore power and I run a ohms test from the ground to the frame it is OL. is this as simple as just replacing the 30A cord?
It does sound like you’ve lost continuity of the ground wire in your shore power cord to the RV chassis. However it’s possibly that there’s a break in the ground conductor between your twist-lock inlet connector and the chassis grounding lug.
Very good, clear information stated in layman’s terms. Some readers may not know which tab is the “hot” on a 30 amp plug. Looking forward to part 3
Great info Mike. If you could create a PDF of all three parts people could download them and make printed copies if need be. I've always kept a information file on any vehicle I have owned. TSB's, shared tech info through groups like this one. Thanks
I can certainly create a printable pdf of this troubleshooting procedure. Thanks for the suggestion.
Good stuff Mike, but who among us out here is actually going to do all this? I do the hot skin test sometimes but that's it. I plug my tester into the pedestal to make sure the connections look good before I plug the trailer in, and that's it.
This test procedure is for troubleshooting the cause of a known hot-skin condition. I get emails all the time from RV owners with their trailers stuck in a repair shop, and the RV technicians can’t determine the cause of a hot-skin shock. It’s actually pretty simple when you understand the basics.
Wait until I publish part 3 which includes all the various current leakage sources.
PS: connect the meter and move the stabilizer. The resistance will jump up and down. Same as corrosion on an electrical connector.
Showing the test to the stabilizer jack screw is not a good place to test. The jack screw itself is not bonded directly to the trailer frame. It passes though the threads to the nut and then through the pivot pins on the legs. All of these are high resistance connections.
Bob, I would tend to disagree. There might be a few milli-ohms of added resistance through the jack screw, but I wouldn’t call it a high resistance connection that could affect the test results.
However, your point is important. For this test you need to probe an unpainted, non-corroded metal spot on the RV that’s directly connected to the chassis. That can be a challenge to find on an older RV.
Interestingly, I used to perform this test on a wheel lug nut, but then I discovered that my trailer axle was mounted in rubber, so there was an extra 40 ohms of resistance from the wheel lug nut to the frame itself.
Who knew? 😁
I still disagree. All the mechanical points on the screw jack may be greasy, insulated, or rusty, pivot points. Just wiggle the stabilizer, every point of contact moves.
Let’s both try an experiment and compare notes. I’m always excited to learn something.
My trailers is in storage right now. But you will have to agree that a moving moving mechanical connection is a poor way to test conductivity. Not much different than using the ball and coupler on a trailer as a substitute for a hard wired ground connection.