electrical presence

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forcebjj

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Doing a bit of investigation in a few j boxes the other day. Doing the usual finding out what powers what before a big kitchen remodel. Using my non contact tester, I was getting a reading on switch legs that were turned off. How long does that "presence" last on a conductor? It was enough to keep my tester chirping. Confused
 
Non contact voltage indicators are only a convenience, use a real meter (low impedance) for true readings.

Roger
 
Non contact testers function from capacitance. If you have other energized conductors in close proximity to your otherwise dead conductors it can be possible to have enough capacitive coupling that it will indicate something. A high impedance meter will read this coupled voltage. As mentioned a low impedance meter is the most reliable method to ensuring whether or not it is "dead". Low impedance meter will put enough load on the test circuit to drain the "capacitor" in those cases where capacitive coupling is the reason for the unexpected voltage.
 
Another consideration...you mention this is with switch legs. If the switches are illuminated, the lamp inside the switch is wired in series across the contacts (not from the hot feed to the EGC terminal), so you will read voltage with the switch in the open (off) position as long as there is a lamp load in the circuit.
 
Craigv said:
Another consideration...you mention this is with switch legs. If the switches are illuminated, the lamp inside the switch is wired in series across the contacts (not from the hot feed to the EGC terminal), so you will read voltage with the switch in the open (off) position as long as there is a lamp load in the circuit.
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Also should someone have switched the grounded conductor instead of the ungrounded conductor your switch leg lead from the light will be "hot" anytime the switch is open.
 
forcebjj said:
Doing a bit of investigation in a few j boxes the other day. Doing the usual finding out what powers what before a big kitchen remodel. Using my non contact tester, I was getting a reading on switch legs that were turned off. How long does that "presence" last on a conductor? It was enough to keep my tester chirping. Confused
Click to expand...
It's not a matter of time. Voltage induced on a de-energized wire by a nearby energized wire will remain as long as the energized wire is energized.

A non-contact tester will tell you that power is present, and little else. Iuse a solenoid tester for everything except when I need to measure the actual voltage.
 
I use a wiggy and a volt tic to trace circuits that are open or shorted. I can energize the circuit from a cord through my wiggy and trace the voltage. A quick and easy circuit tracer
Helps in finding broken neutrals.

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