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Old 02-02-2009, 06:07 PM   #1
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Voltage on my grounding wire


Hey folks - I have removed some old flourescent lighting and want to replace it with something else. When I touch my circuit tester to the black and white wires, I get a dim, faint light. When I touch it to the black wire and the "ground" wire, I get a full reading - what the heck is going on - how can I be getting a circut on all 3 wires? HELP!!! BTW - the wiring is not the modern NM in a white casing - it's in a brown casing, if that's any help. Anyway - I need to get this sorted PDQ - any help, folks????

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Old 02-02-2009, 06:43 PM   #2
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Voltage on my grounding wire


You should actually get a full reading (115V) between the hot (black) wire ane either neutral (white) or ground (bare copper). Neutral and ground are required to be bonded in the main panel (but not in sub panels), so they should both be at 0V to ground.

If you're getting a brighter glow between hot and ground than from hot to neutral, it most likely indicates that the circuit is mis-wireed.
There are a few possibilities, including one that is extremely dangerous, where the ground conductor is hot.

The best test is to use an incandescent light bulb. 25 watts should do.

ALWAYS KILL POWER AT THE BREAKER BEFORE MAKING OR BREAKING ANY CONNECTIONS. Use your little voltage tester to check that you have indeed killed power before proceeding.

Connect the lamp between hot and neutral, apply power, and measure the voltage at the test socket.
You should get 115V (or 110, 120, or whatever your nominal line voltage is).

Connect the test lamp between hot and ground. You should get the same reading and lamp indication that you got between hot and neutral.

You should get 0V, or just a few millivolts between neutral and ground, but be very careful when making the measurement. Leave your meter set to read 150VAC, so you don't destroy your meter (or at least blow its fuse) if there is a lot more voltage there.
You should not need to connect the lamp to test the neutral to ground voltage. There should never be any voltage, regardless of the load.

Use extreme caution in this situation. You don't know what is hot, and what is not, so assume that any conductor can be hot.
Always shut off power at the breaker before making or breaking any connections, even if it's the ground or neutral wires.

I'm sure that as this thread develops, you will get a good idea of what your situation is.

FW

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Last edited by KE2KB; 02-02-2009 at 06:46 PM.
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Old 02-02-2009, 07:48 PM   #3
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Voltage on my grounding wire


good advice as all ways KE . Take a look at the switch(s) and see whats happening there. Could be one of those " I need a three wire but I'll use this two wire . . ."
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Old 02-02-2009, 08:58 PM   #4
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Voltage on my grounding wire


Quote:
Originally Posted by II Weeks View Post
good advice as all ways KE . Take a look at the switch(s) and see whats happening there. Could be one of those " I need a three wire but I'll use this two wire . . ."
Good point. That's what happened in my attic. The BX is 2-wire, but there are two hots, and guess what... neutral is the outer sheath!
My brother found out for me when we were running our model trains. He happened to touch the BX while the fan (10A) was running, and said that it was warm.
I immediately connected the fan to another circuit. Rewiring the old circuits now.

FW
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