How does a home inspector use a tic-tracer (non-contact voltage tester) for safety when doing electrical inspections?
Friday, June 22, 2018
Both of our fathers worked with electricity in their careers as an elevator mechanic and a communications technician for an airline. And both of them taught us the old-school way to check to see if something was electrified and could shock you, possibly to death: touch it lightly with a knuckle of the back of your hand so that, if it was “hot,” the natural contraction of the muscles in your arm when shocked would make it pull away safely. However, using a brief high-voltage shock as a diagnostic tool has gone out style, and now we use a tic-tracer instead.
The pen-shaped device utilizes the principle of “capacitive coupling” to recognize the electromagnetic field that an alternating current creates in the air around it. The back-and-forth pulsing of the a/c electrical charge makes the field even if no current is flowing. A wire or metal surface only has to be electrically “live” and ready to complete a circuit for it to be recognized.
There are different configurations of non-contact voltage testers, and they have varying levels of sensitivity. Some are always “on” and ready for testing, others require holding down a button to activate them. They may use a flashing light, beeping sound, or both to indicate that a/c voltage has been detected. We use one that has an “on” button, variable sensitivity dial, and both beeping and a flashing light to be sure it gets our attention in the presence of a/c voltage.
Here’s four places where a tic-tracer is a useful safety tool for any home inspector:
- Approaching an electric panel to remove the dead front and examine the wiring - If you put a tic-tracer near the dead front of the panel and it lights up, that means either the dead front is electrified and could shock you when you try to take it off or the grounding of the box is faulty. If the box has a good connection to the grounding wire, it will essentially absorb the electrical field and not make the tic-tracer go off. We don’t try to determine which problem it is, just write it up for evaluation by an electrician and leave the dead front in place.
Always, always, always check the dead front with a tic-tracer before touching it. We rarely get a positive reading, but all it takes is one to kill you. The idea for this article came about because all three subpanels in a dysfunctional old house lit it up this morning.
- Inspecting the crawl space under a home - Before our home inspection career, back when we were building contractors in Key West, a fireman moonlighting as a plumber was electrocuted working in the crawl space under a house in Old Town. A section of metal pipe was electrified and he was laying on his back on wet ground. Grabbing the pipe completed a circuit to ground and the electricity made sure he couldn’t let go. It was front-page news.
Loose wires, or wires with deteriorated insulation are also a threat. Sometimes it’s just a piece of scrap wire with the other end buried in the dirt, or possibly a circuit abandoned long ago, or it could be electrified and dangerous. We hold the tic-tracer up to metal and wires above and below us before proceeding when crawling under a house.
- Checking for grounding of appliance cabinets - If you hold a tic-tracer up to the side of a refrigerator and it beeps, it is likely that there is a 2-slot ungrounded receptacle behind it with a “cheater plug” to enable the connection of the 3-prong grounded cord, or the ground connection is loose somewhere in the appliance. If the refrigerator was grounded, the cabinet would absorb the electromagnetic field. It is also possible that the cabinet is electrically live and could shock someone when the floor is wet.
- Inspecting an attic - Same as a crawl space but, or some reason, loose live wires are more likely in an attic than a crawl space. Plus, a tic-tracer can be useful for evaluating knob-and-tube wiring in old house attics. Sometimes part of the old wiring has been abandoned in place, while other knob-and-tube circuits are still live, and a tic-tracer can be used to sort it out.
The tic-tracer is not a perfect tool. It may register a false positive from what is called a “ghost current.” An example would be a disconnected length of wiring in an attic running next to live wiring, which would absorb some of the electromagnetic field of the adjacent wires. Adjusting the tic-tracer sensitivity is one way to compensate for a ghost current.
It also does not recognize direct current (DC) because there is no electromagnetic field generated, and any type of shielded cord or conduit will not register. Manufacturers recommend testing the tic-tracer against a known a/c current source before using it each day.
You definitely should be aware of a tic-tracer’s limitations. Just to be sure, we still use our dads’ back of the hand technique, even after the tic-tracer indicates everything is “okey-dokey,” as they would say.
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