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#71141 - 10/23/06 03:20 PM Multi-wire branch circuit voltage readings
poorboy Offline
Member

Registered: 06/02/05
Posts: 128
Loc: Central Maine
New install in a retail store. Adjacent receptacles in a telcom room on a 12/3 MC homerun. If nothing is plugged in, you have 120 V to neutral on each circuit. If you plug in a security system transformer you have 200+ volts to neutral on the other circuit(which still has nothing plugged into it). If I unplug that and plug my 3 prong tester into the circuit I Read 176 volts to neutral on the other circuit. The condition came to light when the inspector plugged his 3 prong tester in to the second circuit with the transformer plugged into the first and saw two green lights and an orange. What am I missing here? Checked the wiring and found no problem---ckts are on different phases and share a neutral. 120 volts is derived from a transformer since this is a 480/277 service.

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#71142 - 10/23/06 03:25 PM Re: Multi-wire branch circuit voltage readings
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
It really appears the neutral is not correctly wired.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#71143 - 10/23/06 03:57 PM Re: Multi-wire branch circuit voltage readings
JoeTestingEngr Offline
Member

Registered: 11/04/05
Posts: 786
Loc: Chicago, Il.
I sure hope that your Neutral is coming from the bonded secondary center tap of that transformer.
Joe

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#71144 - 10/23/06 04:04 PM Re: Multi-wire branch circuit voltage readings
Zapped Offline
Member

Registered: 10/01/02
Posts: 481
Loc: Huntington Beach, CA, USA
I've seen very similar readings from loose or mis-wired neutrals also. That would be my first guess. Please let us know what you find out...

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#71145 - 10/24/06 01:21 PM Re: Multi-wire branch circuit voltage readings
poorboy Offline
Member

Registered: 06/02/05
Posts: 128
Loc: Central Maine
Went back and looked in the panel today. The guy who made it up had the neutral from the 12/3 spliced to a piece of white THHN because it would not quite reach the neutral strip on the bottom of the panel. I followed this THHN down, across the bottom of the panel, past the neutral strip, back up the other side of the panel where it was wirenutted to the neutral tail from a GFCI breaker. Apparantly he had intended to use this piece of THHN to lengthen both neutrals so they would reach the strip. All he forgot was to CUT IT IN THE MIDDLE AND ATTACH EACH ONE TO THE NEUTRAL STRIP!!! Keep your eye on your help and never assume anything.

[This message has been edited by poorboy (edited 10-24-2006).]

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#71146 - 10/24/06 01:37 PM Re: Multi-wire branch circuit voltage readings
SteveFehr Offline
Member

Registered: 03/19/05
Posts: 1192
Loc: Chesapeake, VA
LOL!!!! I shouldn't laugh, though, sounds like something I'd do!

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#71147 - 10/25/06 05:56 AM Re: Multi-wire branch circuit voltage readings
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
It's amazing how much better something works if it's wired up correctly!

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#71148 - 10/25/06 06:15 AM Re: Multi-wire branch circuit voltage readings
Zapped Offline
Member

Registered: 10/01/02
Posts: 481
Loc: Huntington Beach, CA, USA
Thanks for the update poorboy. I'll keep that information in my troubleshooting brain-file...

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