# Solve this Head-scratcher!



## 480sparky (Sep 20, 2007)

Wrapped up a small 'resi/comm' job this morning......

An apartment management firm was taking two garage bays and turning it into a maintenance shop for the work crew. Up to now, they've have everything plugged into the receptacle for the door operator. They wanted a slug of receps, as well as a small heater and a range & dryer receps for testing appliances.

Got it all done, and turned on the power. To kaboom..... that's a good sign. Went to check the GFCIs, and my 3-light plug-in tester showed "Hot/Neutral Reversed". Dammit! Oh well, I never claimed to be perfect.

So I turn the power off, remove the GFCI and the wires are correct...... black to the gold screw, white to the silver. I turn power back on, and the black lights up my NC tester.

"Oh, don't tell me I got the black & white mixed up in the panel!?!?!?! I can't be THAT stupid!" So the panel cover comes off, and the black goes to the breaker, white to the neutral bar. NC tester shows the black is hot.

WTF? So I check other receps on the circuit....... same thing..... Hot/Neutral reversed. Could my tester have suddenly failed? The maintenance guys were there, and they used their spiffy brand-new one. Same indication...... H/N reversed.

At this point I break out the Fluke. Black is 122v to ground, white is 0v. Every receptacle on this circuit meters the same (correct polarity), but the 3-light tester shows H/N reversed.

FYI..... wiring is THHN & EMT, 4-sq boxes & raised covers, SqD QO panel.


Anyone wanna take a guess at the cause?





Oh, and yes, I did find it, and it has been corrected.


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## B W E (May 1, 2011)

Bad gfi?


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## muck (Jun 30, 2008)

240 V at the panel? Did u check both legs?


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## BuzzKill (Oct 27, 2008)

ground and N tapped in a jbox somewhere?


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## Chris1971 (Dec 27, 2010)

Screw terminals on gfci receptacles backwards? Pinched wire? I don't know? I give up. The suspense is killing me. I might as well jump off of a building. Please do tell.:thumbsup:


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## jmsmith (Sep 10, 2011)

Did you mistakenly tie your 120 to the load side of the GFCI? I know I've done that before.
:blink:


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## jarhead0531 (Jun 1, 2010)

Every time I see a H-N reverse on a plug in tester it usually mean an open neutral someplace. What did I win??


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## wildleg (Apr 12, 2009)

a wire had come off in a jbox and the pipe was energized, but the pipework wasn't connected properly and they used it for a ground so it didn't trip the breaker ?


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## Wireman191 (Aug 28, 2011)

If the panel was not properly bonded/grounded could that cause it?


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## jmsmith (Sep 10, 2011)

jmsmith said:


> Did you mistakenly tie your 120 to the load side of the GFCI? I know I've done that before.
> :blink:


BTW, in my haste, I have been known to not tag my feed when using the same color wire in conduit, resulting in having to disconnect BOTH blacks in order to verify my hot. Just a brain fart, I guess!
:laughing:


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## Meadow (Jan 14, 2011)

No neutral to ground bond at trany or disconnect? Energized ground?


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## Chris1971 (Dec 27, 2010)

So, what was the final outcome?


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## 480sparky (Sep 20, 2007)

wildleg said:


> a wire had come off in a jbox and the pipe was energized, but the pipework wasn't connected properly and they used it for a ground so it didn't trip the breaker ?


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## Big John (May 23, 2010)

Nice. I'm afraid to ask how you found the energized pipe.









-John


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## 480sparky (Sep 20, 2007)

Big John said:


> Nice. I'm afraid to ask how you found the energized pipe.
> 
> 
> 
> ...


NC tester.


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## RIVETER (Sep 26, 2009)

480sparky said:


>


How did you not have a good conduit system? Did you admit that to anyone?


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## 480sparky (Sep 20, 2007)

RIVETER said:


> How did you not have a good conduit system? Did you admit that to anyone?


I used some of the existing piping.


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## RIVETER (Sep 26, 2009)

480sparky said:


> I used some of the existing piping.


Since the conduit will carry the vast majority of a fault current in a properly grounded/bonded system, maybe a resistance check could be performed from the source of the power to the point at which you are tieing in.


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## LARMGUY (Aug 22, 2010)

480sparky said:


> I used some of the existing piping.


 
That's what I would have said too. :whistling2:


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## jmsmith (Sep 10, 2011)

480sparky said:


> I used some of the existing piping.


Thanks for the lesson-I learned NOT TO ASSUME anything, such as the pipe being run from scratch, or only mentioning wire/terminal combos. Lesson learned!
:thumbsup:
-Jim


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## BuzzKill (Oct 27, 2008)

RIVETER said:


> Since the conduit will carry the vast majority of a fault current in a properly grounded/bonded system, maybe a resistance check could be performed from the source of the power to the point at which you are tieing in.


you and you're damn grounding/bonding sh*t: have you not figured it out by now? lol :laughing:


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## BuzzKill (Oct 27, 2008)

wildleg said:


> a wire had come off in a jbox and the pipe was energized, but the pipework wasn't connected properly and they used it for a ground so it didn't trip the breaker ?


dammit! this sounded quite plausible when I read it this afternoon.


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## frenchelectrican (Mar 15, 2007)

BuzzKill said:


> dammit! this sounded quite plausible when I read it this afternoon.


I have fair share with the same situation from time to time when the conduit is not really " bonded " and show a floating power like what Ken did went thru and some of exsting fittings { coupling or connectors } some case not really bonded correct especailly with exsting installments that sometime you have to take it with grain of salt to verify it.

Merci,
Marc


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## BuzzKill (Oct 27, 2008)

frenchelectrican said:


> I have fair share with the same situation from time to time when the conduit is not really " bonded " and show a floating power like what Ken did went thru and some of exsting fittings { coupling or connectors } some case not really bonded correct especailly with exsting installments that sometime you have to take it with grain of salt to verify it.
> 
> Merci,
> Marc


Man, whenever I get to Paris, we gotta go drankin!


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## frenchelectrican (Mar 15, 2007)

BuzzKill said:


> Man, whenever I get to Paris, we gotta go drankin!


Sure Buzzkill I will be glad to take that offer.

Merci,
Marc


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## RGH (Sep 12, 2011)

Had one like that last summer wtf 2hrs chasing a short....put new 4way new recp's fire her up and bang .Opened it up 2x The h/o told me the sw to garage was not working. My stuff fine damn switch still shorten...I get continuity bx to hot ....scatchin my head...when did ya get the new roof and gutters? About the time the switch stopped working 12" spike right thru bx . 2hrs looking thru 3 2gangs/the 4 way and receps


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## BuzzKill (Oct 27, 2008)

480sparky said:


> I used some of the existing piping.


yep! that was the teaser hint.


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