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Multi-wire branch circuit voltage readings #71141 10/23/06 06:20 PM
Joined: Jun 2005
Posts: 124
P
poorboy Offline OP
Member
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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Re: Multi-wire branch circuit voltage readings #71142 10/23/06 06:25 PM
Joined: Jan 2003
Posts: 4,391
I
iwire Offline
Moderator
It really appears the neutral is not correctly wired.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Re: Multi-wire branch circuit voltage readings #71143 10/23/06 06:57 PM
Joined: Nov 2005
Posts: 806
J
JoeTestingEngr Offline
Member
I sure hope that your Neutral is coming from the bonded secondary center tap of that transformer.
Joe

Re: Multi-wire branch circuit voltage readings #71144 10/23/06 07:04 PM
Joined: Oct 2002
Posts: 482
Z
Zapped Offline
Member
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...

Re: Multi-wire branch circuit voltage readings #71145 10/24/06 04:21 PM
Joined: Jun 2005
Posts: 124
P
poorboy Offline OP
Member
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).]

Re: Multi-wire branch circuit voltage readings #71146 10/24/06 04:37 PM
Joined: Mar 2005
Posts: 1,213
S
SteveFehr Offline
Member
LOL!!!! I shouldn't laugh, though, sounds like something I'd do!

Re: Multi-wire branch circuit voltage readings #71147 10/25/06 08:56 AM
Joined: Aug 2001
Posts: 7,520
P
pauluk Offline
Member
It's amazing how much better something works if it's wired up correctly! [Linked Image]

Re: Multi-wire branch circuit voltage readings #71148 10/25/06 09:15 AM
Joined: Oct 2002
Posts: 482
Z
Zapped Offline
Member
Thanks for the update poorboy. I'll keep that information in my troubleshooting brain-file...


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