RV Doctor – RV Hot Skin Test How-To

Dear Gary,
How do you perform a hot skin test on a recreation vehicle? Also I’ve heard you should still hot skin test a fiberglass sided RV by checking faucets, door frames and windows. How do you do that on a slick side motorhome? – Jay Jones, (Silverdale, WA)

Answer:

Jay, it is indeed true that every RV should have a hot skin test performed if there is any question about its electrical integrity, including those with fiberglass or plastic siding. Receiving a slight shock or tingle as you step into a motorhome is a good clue that something is amiss.

For a complete hot skin test all you need is an accurate volt-Ohm meter, preferably digital. Here’s how the pros do it. First, be sure all the RV circuit breakers are turned on. Plug the shoreline cord into an external source of 120-volts AC. Set the voltmeter to the 250-volt scale. To test for an electrical short, position the red test lead on a bare metal portion of the RV; the frame, entry step, door frame, etc. Connect the negative test lead of the voltmeter to earth ground such as a water pipe or the ground conductor in the panelboard distribution box of the external power source. Run the test multiple times using several different metallic components on the RV.

• A “0” reading indicates no leakage or voltage on the skin.
• Any voltage reading indicates a definite electrical short and further testing is in order.

Always perform this test at least three times at different metallic locations on the motorhome and be sure to reverse the leads on the voltmeter to be sure no voltage is leaking or shorting. The hot skin test is necessary even if the motorhome is made of fiberglass or other non-metal components. The frame, chassis, copper tubing and metal trim pieces on the coach can still conduct voltage.

Hot skin issues with RVs are typically high resistance electrical shorts which do not usually trip breakers or blow fuses. This type of short may result from the insulation on the conductors rubbing thin or breaking down through normal wear or abuse. Problems occur, but not a dead short. In some cases, the white, neutral wire may be cross-connected to the ground conductor. This may cause reverse polarity which would then by-pass circuit breakers resulting in no over-current protection.

If the hot skin test reveals a high resistance short, disconnect from all sources of 120-volts AC and do not plug the motorhome in until all shorts have been eliminated. It is recommended that a professional RV service technician or an electrician make the necessary repairs before powering up that motorhome on AC again.

(Please feel free to comment, however, please also note that due to the volume of communications I receive from multiple channels I cannot guarantee a personal response in every instance. However, questions of an overall general interest may be considered and published in an upcoming RV Doctor column.)