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#23437 - 03/18/03 09:39 AM Open Neutral?  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
I have what appears to be an open neutral problem. I'm getting 120 volts from neutral to ground. Funny thing though, the 3-wire plug-in tester shows hot & ground reversed.
I know nobody switched the wires, because the problem is intermittent, and sometimes it is OK.
Does anyone know the internal circuitry of the plug-in tester, and why it would show hot & ground reversed when it appears to be an open neutral?



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#23438 - 03/18/03 12:02 PM Re: Open Neutral?  
classicsat  Offline
Joined: Nov 2002
Posts: 456
The circuitry is simple, three neon lamps,
one connected H-N another H-G and the third N-G.

#23439 - 03/18/03 12:06 PM Re: Open Neutral?  
SvenNYC  Offline
Joined: Aug 2002
Posts: 1,691
New York City
My friend Paul Stenning in the UK built one from scratch using a little plastic enclosure mounted to a BS-1363 cord cap.

Keep in mind this is for UK plug configurations and voltages but the theory should be the same.

Follow this link:

#23440 - 03/19/03 07:44 AM Re: Open Neutral?  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Thanks for input guys. Very helpful!
I printed your drawing and drew 3 parallel loads with one of the switches closed, the tester plugged in downstream of the loads, and the neutral open at the source. Tracing the current flow, it seems that this situation will illuminate the the same lamp configuration as L & G reversed.


[This message has been edited by Redsy (edited 03-19-2003).]

#23441 - 03/19/03 07:00 PM Re: Open Neutral?  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
I always recommend people using these testers to be very skeptical at what the printed table says is the problem.

Many RV drivers here carry one to check the integrity of power hook-ups on campsites, and I recall the exact same problem arising in a letter to a journal I write for. Once the loads inside the RV were all disconnected, the tester would then correctly indicate an open neutral.

#23442 - 03/25/03 08:52 AM Re: Open Neutral?  
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
Found it. Open neutral. With the switch to a load closed, the tester shows L & G reversed.

Thanks for drawing Sven, it helped keep me on track. [Linked Image]


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