Volgage porve caution

Aug 25, 2008 7 Replies
I

I own a "Circuit Alert" made by GB Instruments. (had it for over 6 years, has new batteries). These are the probes that you place in the vicinity of a live circuit and the instrument 'chirps' in response.



I just discovered that it does not detect current, or voltage, when you wave it around a 240 volt cable. While it 'chirps' happily within 3-4 inches of a 120 volt wire or cable, it will not do so for 240 volts. Won't detect my main house service (6 gauge, bundled in sheathing), air conditioning feed (10 gauge, bundled in sheathing) or any other 240 volt bundled source. Of course, if you go to the end of the feed and wave the tool near either of the 120 volt legs, it shows positive.



I'm doing a lot of demolition work around the house and am quite surprised by the above results. I suppose one leg of the 240 feed is out of phase with the other and they cancel each other? Any comments.



Be careful our there.



Ivan Vegvary


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I

Subject should have said probe, note porve.

Sorry,

Ivan Vegvary

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W

(...)

I think that is correct. Phase cancellation, but also proximity to the ground conductor would limit the electric field in that situation.

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Mfr states the only gotcha is conductors shielded by conduit or equivalent.

I wonder if you can get a reading by repositioning/rotating the tool near a split phase bundled conductor to pick off the portion of the electric field that leaks?

--Winston

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J

You hit the nail on the head. Typical 240 volt single-phase service has one wire going positive while the other goes negative, the average always being zero. The voltage from either wire to ground is 120.

I bet a 3-phase feeder will also escape notice by this circuit alert.

The Circuit Alert gadget sounds dangerous.

Joe Gwinn

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J

I discovered the same thing with a Greenlee detector while cutting out some old dead wires. Well, one of them wasn't so dead. 220v worth of excitement!

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G

Odd...my several do read 240/480

"Confiscating wealth from those who have earned it, inherited it, or got lucky is never going to help 'the poor.' Poverty isn't caused by some people having more money than others, just as obesity isn't caused by McDonald's serving super-sized orders of French fries Poverty, like obesity, is caused by the life choices that dictate results." - John Tucci,

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K

I'm going to have to check mine. Thanks for the heads up. Karl

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