Strange leakage current

[BoscoMN]

I don’t know for sure how much, if any, this poses as a safety risk so I wanted to throw it out onto the forum for discussion. While laying on a heating pad in the bed I reached up to turn on the reading light and noticed that “feeling” one gets when touching a metal surface that has a slight amount of current that flows through your body to ground. I describe it as if the metal surface is a little “sticky” as you gently brush the back of your hand over it.

1. I did not have a shirt on so I made good contact with the heating pad.
2. The 2 wire heating pad is in excellent condition with no apparent conditions that would provide direct contact to wires, it was not wet, etc.
3. The feeling was present when the heating pad was powered on or off, but not when it was unplugged.
4. The 120 VAC plug next to the bed showed no errors when I checked it with a plug-in tester.
5. I have a Hughes Autotransformer plugged into the pedestal 30A circuit.
6. Using a Fluke NCVT-1 Voltage Tester on the skin of the Airstream indicated no voltage/current leakage to ground.
7. No voltage or current differential between the Airstream shell to earth ground when measured with a multimeter.
8. I do tie the external Airstream coax cables to earth ground as part of my antenna setup. I wonder if this ties the negative side of the 12 VDC power converter to earth ground which subsequently ties it to the 120 VAC ground as well.
9. Using a $30 multimeter, there is no voltage/current shown between myself and the metal on the reading light while laying on the activated heating pad, even though I can feel the difference of this “surface tension” when I brush my hand on the side of the reading light.

Any ideas?

[Tim A.]

Sounds to me like the heating pad has an internal electrical fault and you are getting some ground through the lamp. I suggest that the fault is 110v and not in the 12v system. You shouldn't feel 12 volts.

Tim

[Mattirs]

What are you testing A/C or D/C current? Sounds like what you are feeling is A/C. Also, is the amp setting low enough?

[BoscoMN]

The only part I see that the 12 VDC system could play in this is having the -12 VDC tied to the metal of the Airstream by one of the devices using 12 volts. Even then I don’t know how it could be a factor. And I agree with you the current and voltage level of the 12 VDC system on its own cannot cause this situation.

I set the meter up using the 200 milliamperes setting and AC for both current and voltage.

When back home I will try out the same thing using my second heating pad to see if the one in the Airstream is faulty. I am guessing that the switch does not break the hot side of the circuit, thus keeping the heating wire connected to the 120 VAC hot side of the circuit. Then the wire only has to have a slight break in its insulation to enable my bare skin to gain enough contact through the heating pad cloth cover.

Since owning the metal Airstream I have always been wary of any electrical device that had only 2 prongs instead of 3. Then your protection is only as good as that device’s internal insulating design. A perfect example is our metal toaster. If the hot side of the internal wiring were to short to the metal case, you could get quite the shock if you touched the toaster and the wall or stove.

[overlander63]

Static electricity?

[BoscoMN]

No, it lasts for as long as the heating pad is plugged in and I want to rub the back of my hand on the reading light. This is a feeling I am pretty familiar with as I have experienced it a few times over the years (never on an RV). As a kid I did a lot of electrical and electronic hobby projects...