There is a long standing myth among home inspectors and others, that one should always touch the electrical panel cover with the back of your hand, specifically your right hand to see if the cover is energized.
There are some problems with this approach. All touching it with your hand does is tell you that YOU are not grounded. You are isolated from the ground (rubber sole shoes, floor coverings, location etc). The idea is, if you were to get a shock from it, your muscles would contract pulling your hand away from the cover instead of toward it.
Some recommend using an NCVT (non-contact voltage tester) to check the cover. The assumption is if the NCVT is activated the cover must be energized. But again this is not true, because there are ways to “induce” voltage on the cover without it being truly energized. In terms of being energized, this would be more of a “false positive” indication. Activation of the NCVT is at the very least an indication the panel is not properly grounded, but it does not “necessarily” mean it is energized. In fact it is VERY rare the cover would actually be energized–but because it is possible we must be cautious.
So what is the best way to check to see if the panel cover is energized?
Well of course use of a multi-meter or equivalent is a good way–but finding locations to put the second lead is not always easy to do, without carrying a coil of wire to make one of the leads long enough.
There is another way to test it that is not complicated.
This method involves using both your hand and an NCVT.
In the video below, you will see a wire stuck in a receptacle that is connected to a metal box with a metal cover that symbolizes an electrical panel or ANY metal component that could be energized. The multimeter shows the metal box at 122.5 volts (leads run from cover plate to neutral slot of nearby receptacle).
The NCVT indicates the cover is energized and yet I can hold onto the cover without getting a shock (because I am isolated from ground).
Watch what happens when I touch the box and touch the energized wire. The NCVT turns “OFF.” Surely magic, right?
Not magic–this is just the way they work. The NCVT cannot “see” voltage on grounded conductors (only ungrounded conductors–hot wires), and even while my body is not physically grounded, it represents enough similar characteristics to confuse the NCVT .
As I move the NCVT away from the wire, notice how it lights up again? This method, with one hand on the cover plate and the NCVT in the other hand, will tell you the cover is actually energized. If it were not energized, the NCVT would simply not activate.
Always, always, always make sure whenever you are working on any electrical component that you yourself are in no way in contact with something grounded. And, such testing should only be done by qualified parties.
By Charles Buell Real Estate Inspections in Seattle