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#1533 - 05/16/01 04:20 AM Neutrals from different panels
Joe Tedesco Offline
Member

Registered: 10/07/00
Posts: 3325
Loc: Boston, Massachusetts USA
Heres a good question from Mike Fox in Indiana and I would appreciate your answers:


"Subject:

Neutrals from different panels
Date:

Wed, 09 May 2001 15:03:19 -0500
From:

FoxM@Mail.ips.k12.in.us
To:

codeviolations@netscape.net


Joe,
I enjoy your "Code Violations" section and wanted to quiz you on a certain point. Several times in my career as an
electrician I have run into this potentially dangerous situation. This usually occurs in a commercial or industrial
plant where there are many distribution panels through out the building. An electrician is asked to change a panel
interior due to age and availability of breakers. After the proper wire bending radius is checked and OK'd with the
new interior manufacturer the electrician has the go to put the new interior in the old tub. He locks and tags out
the feeder to the panel but ends up getting shocked when lifting the panel neutral. The reason he was shocked is due
to another electricians mistake. Someone inadvertently tied the grounded conductor from another panel to the neutral
of the panel being upgraded. Even with the panel feeder de-energized current is passing through the neutral of the
panel being upgraded. Of course when the neutral is lifted you have the potential of the phase voltage in your hand.
If the electrician didn't see the spark he could potentially become a series load to ground. I have talked to other
experts about this and they act as though this is common knowledge and not a big deal. I can tell you I teach code
courses and each year I pose this situation to my students. Many of them are seasoned electricians and usually only a
few have encountered this. I think we need to identify the grounded conductors with suitable wire tags corresponding
to the proper panel number. What are your feelings on this? Thanks, Mike Fox (Indiana Electrical License Prep)

Added note by mike: "The electrician would be shocked by the neutral bar not the neutral feeder conductor."

[This message has been edited by Joe Tedesco (edited 05-16-2001).]
_________________________
Joe Tedesco, NEC Consultant

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#1534 - 05/16/01 05:35 AM Re: Neutrals from different panels
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
Joe,
I've run across this a number of times on service work. I'm not sure that more code rules to require neutral ID will help. The type of electrician that would tie into a neutral without checking to see where it comes from, would not be likely to look at the wire tags.
Don(resqcapt19)
_________________________
Don(resqcapt19)

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#1535 - 05/16/01 07:12 AM Re: Neutrals from different panels
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
Someone inadvertently tied the grounded conductor from another panel to the neutral

so has this 'other panel' been fed it's hots from one source, and nuetral from another?

if so, i would say it's a big deal...


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#1536 - 05/16/01 07:32 PM Re: Neutrals from different panels
doc Offline
Member

Registered: 11/25/00
Posts: 119
Loc: Texas
well being more in a maintenance field and having worked in several plants most of the people that do electric are just running wires and sticking them in a slot they have no idea why this wire should go here and this one over here and so if you put a tag on all the guy will do is say " hum wonder what that tag and those words mean " he will then go get his boss or someone in management and they will tell him " oh ,dont worry about that just do it "
A great example is where i worked for nine years they hired a guy and brought him in to nudge me out we went to run a sub panel wich was a 100 amp {3 phase }this guy drags out some wire a pieces of #6 and 2 pieces of # 8 no neutral and no ground needed the grund as he was using flex long story short to him they wanted power and he was giving it to them no idea of what he was doing
and yep the guy is still there andf still running wire.
So until u can get companies to listen and can teach eggheads like this guy you will never stop these types of problems with codes or rules
AND here lately I have been in a lot of plants if u go back and look at some of my post for back in late last year and earlier part of thids year u will see some of these same type questions ask
_________________________
MAY THE SUN SHINE ON YOUR FACE IN THE MORNING AND YOU AWAKE WITH A SMILE

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#1537 - 07/28/02 07:04 AM Re: Neutrals from different panels
Joe Tedesco Offline
Member

Registered: 10/07/00
Posts: 3325
Loc: Boston, Massachusetts USA
Define a NEUTRAL so it can be sent in as a proposal to NFPA for the 2005 NEC.
_________________________
Joe Tedesco, NEC Consultant

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#1538 - 07/28/02 02:32 PM Re: Neutrals from different panels
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Crossing neutrals/grounded conductors is a problem here as well. I've often found it in residential wiring where somebody has modified an older lighting circuit which was originally run in single cables which may be widely separated -- If they need a neutral they just take the nearest one available.

Our "code" also specifies that once a neutral/grounded conductor leaves a panel (either for a branch circuit or as a sub-feeder), then it must be used exclusively for that circuit -- No cross connections.

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#1539 - 07/28/02 02:44 PM Re: Neutrals from different panels
Gwz Offline
Member

Registered: 04/29/02
Posts: 199
A circuit installation where the Grounded Conductor from a different panelboard (source) would be a violation of 300.4(B) and 300.20(A).

*****

Hey, if the motor or light (etc.) works when the power is applied, then it must be wired per the Code !!

Seems many individuals support that thought.

*****

Glenn

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#1540 - 07/28/02 04:42 PM Re: Neutrals from different panels
harold endean Offline
Member

Registered: 02/16/02
Posts: 2248
Loc: Boonton, NJ
Joe,

Had my own personal experinece with crossed neutrals. There were two 12-3 RX wires in a panel. when we hooked up the first on and turned it on, we blew up 4 TV's in 4 different apartments. The 2 phase legs in the one cable was tied to the neutral in the second cable. In the second cable only the beutral was used. The 2 phase wires were not even hooked up.

Caper

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#1541 - 07/28/02 05:05 PM Re: Neutrals from different panels
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
This became a real interesting problem in a small multi-tenant office building a couple of years ago. Associate moves into larger square footage, but finds that some CRT computer monitors would jiggle and make work on them impossible. Was able to borrow a calibrated low-frequency electromagnetic-field probe and take some measurements.

Traced it to a 100A 208Y panelboard on a lower floor. A ~36x36-inch piece of sheet metal slid around on the floor would change the interference. In the end, a large clip-on CT placed around the feeder conductors into the lower panel read about 15 amps—pointing to swapped/shared branch-circuit neutral conductors. In the mean time, the guy with the headache was able to budget two nice new 18-inch LCD displays in place of the CRTs, so he was finally happy.

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