None of my multimeter test probes have alligator clips. About 50% of the time at campgrounds, the RV is situated on concrete and the ground itself isn't close enough to allow placing a meter between a screwdriver stuck into it and some metal on the RV. However, pedestals are ALWAYS in the ground and an NCVT should work there, if I am correctly understand what you're explaining. Trying to test the polarity on a standard pedestal is often a pain - the cover flap keeps smacking you in your head as you place the probes into the outlet to make contact while trying to read your multimeter. At home, our motorhome is usually parked in our steel garage with concrete floor and plugged into a 50 amp outlet, which can be polarity tested with a meter.
A NCVT should always work to find a hot-skin on a RV, but using a AC meter between the RV chassis and pedestal box may not work properly if there’s a Reflected Hot Skin Voltage energizing the pedestal box to 120 volts. For field diagnostics I built a pair of 75 ft meter extensions so I could always measure between the RV chassis and earth or pedestal with a Kelvin Bridge Meter. But that’s beyond the scope of this course.
Such an important thing. We were in an very upscale FL campground this past winter. As usual I do a NCT test and all was good. For unknown reasons the next day all sites on the same main panel exhibited electrical problems. Some campers had A/C tripping. When a neighbor came over we checked my rig and my surge protector noted all was fine and working. But as the neighbor placed his hand on my furnace face he felt a tingle. We had a hot surface. The Campground was not friendly when we all started to note the problem. As you say we disconnected and lucky we have a big solar battery bank so we were fine in the hot .heat. The campground brought a (we thought electrician, turns out it was only an RV tech that was nearby) he started checking things and couldn't find the hot skin or anything else. We also confirmed the hot skin was gone. Note even the pedestal had a hot skin when this started. We plugged back in and in less than 5.minutes the hot skin situation came back. We again immediately unplugged and noted the pedestal still had a hot skin all around the exterior of the pedestal. When this tech came by to check our pedestal I warned him it was hot. Although once again it disappeared. He began checking the pedestal and while pulling out the 50 amp receptacle he for strongly shocked by just touching the outer metal ring that holds the receptacle in the box. Very strange. He basically was clueless. Hours later the campground said a licensed electrician would be on site. It was also noted while this tech opened the main box where all the breakers were that the neutral and ground bus bars were not tied together. I have heard that they need to be. Not sure if this was the problem. Later the evening an electrician verified things but no really understanding of what caused the hot skin. Likely because of campground liability. But all was corrected and our final 2.days were uneventful. But knowing hot skin and such is so important in checking regardless of campground looks. Even the biggest and nicest looking can be a potential problem. So thanks full for your articals!!!
Great article Mike! There is an implication that < 40V AC (or the lower sensitivity limit of the NCVT) is safe but something tells me that might not always be true. The fact that the NCVT can sense 40V or more means there is enough leakage from the hot side of the input power line to the RV chassis to develop 40V given the impedance to ground that you are presenting. Is there a chance you can still have a hot skin condition even if your NCVT doesn’t beep at you?
Since you're capacitively coupled to the earth ground, any kind of shoes will work for testing with a NCVT. But if you're up on a fiberglass ladder, your body won't be capacitively coupled to the earth, and you'll probably get a false negative reading.
Question, I tried searching for Part 3 but can't seem to find it. TIA.
I’ll look for the link later today… Thanks
None of my multimeter test probes have alligator clips. About 50% of the time at campgrounds, the RV is situated on concrete and the ground itself isn't close enough to allow placing a meter between a screwdriver stuck into it and some metal on the RV. However, pedestals are ALWAYS in the ground and an NCVT should work there, if I am correctly understand what you're explaining. Trying to test the polarity on a standard pedestal is often a pain - the cover flap keeps smacking you in your head as you place the probes into the outlet to make contact while trying to read your multimeter. At home, our motorhome is usually parked in our steel garage with concrete floor and plugged into a 50 amp outlet, which can be polarity tested with a meter.
A NCVT should always work to find a hot-skin on a RV, but using a AC meter between the RV chassis and pedestal box may not work properly if there’s a Reflected Hot Skin Voltage energizing the pedestal box to 120 volts. For field diagnostics I built a pair of 75 ft meter extensions so I could always measure between the RV chassis and earth or pedestal with a Kelvin Bridge Meter. But that’s beyond the scope of this course.
Such an important thing. We were in an very upscale FL campground this past winter. As usual I do a NCT test and all was good. For unknown reasons the next day all sites on the same main panel exhibited electrical problems. Some campers had A/C tripping. When a neighbor came over we checked my rig and my surge protector noted all was fine and working. But as the neighbor placed his hand on my furnace face he felt a tingle. We had a hot surface. The Campground was not friendly when we all started to note the problem. As you say we disconnected and lucky we have a big solar battery bank so we were fine in the hot .heat. The campground brought a (we thought electrician, turns out it was only an RV tech that was nearby) he started checking things and couldn't find the hot skin or anything else. We also confirmed the hot skin was gone. Note even the pedestal had a hot skin when this started. We plugged back in and in less than 5.minutes the hot skin situation came back. We again immediately unplugged and noted the pedestal still had a hot skin all around the exterior of the pedestal. When this tech came by to check our pedestal I warned him it was hot. Although once again it disappeared. He began checking the pedestal and while pulling out the 50 amp receptacle he for strongly shocked by just touching the outer metal ring that holds the receptacle in the box. Very strange. He basically was clueless. Hours later the campground said a licensed electrician would be on site. It was also noted while this tech opened the main box where all the breakers were that the neutral and ground bus bars were not tied together. I have heard that they need to be. Not sure if this was the problem. Later the evening an electrician verified things but no really understanding of what caused the hot skin. Likely because of campground liability. But all was corrected and our final 2.days were uneventful. But knowing hot skin and such is so important in checking regardless of campground looks. Even the biggest and nicest looking can be a potential problem. So thanks full for your articals!!!
Mike Venti,
Please email your direct contact info to mike@noshockzone.org . I need some clarification on what you observed. Thanks…
That was likely caused by what I call a Reflected Hot-Skin Condition.
And No, the neutral and ground conductors in each pedestal should not be bonded together. Read this https://open.substack.com/pub/rvelectricity/p/whats-a-reflected-hot-skin-voltage
Great article Mike! There is an implication that < 40V AC (or the lower sensitivity limit of the NCVT) is safe but something tells me that might not always be true. The fact that the NCVT can sense 40V or more means there is enough leakage from the hot side of the input power line to the RV chassis to develop 40V given the impedance to ground that you are presenting. Is there a chance you can still have a hot skin condition even if your NCVT doesn’t beep at you?
When doing the NCT yest, do you have to be in bare feet or could you have rubber sole sneakers on?
Since you're capacitively coupled to the earth ground, any kind of shoes will work for testing with a NCVT. But if you're up on a fiberglass ladder, your body won't be capacitively coupled to the earth, and you'll probably get a false negative reading.