?Swapped? Neutral & Ground Condition

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catchtwentytwo

Senior Member
We have a Computer Power Center (PDU) where a contractor mistakenly terminated some 120 volt neutrals on the Isolated Ground Bar. This PDU monitors ground current and eventually alarmed at 10 amps. Every branch circuit is dedicated and terminates in a locking-type receptacle.

The receptacles were tested for correct polarity when installed. I tried using the Ideal SureTest? Circuit Analyzer's Ground Impedance feature and didn't see a "smoking gun" on a test circuit we deliberately mis-wired.

My question is: Are there any practical ways to field test a receptacle for a ?swapped? Neutral & Ground condition? Assume that it could be caused at the panel or the receptacle.

[ August 19, 2005, 01:17 PM: Message edited by: catchtwentytwo ]
 

ron

Senior Member
Re: ?Swapped? Neutral & Ground Condition

In the PDU, most likely because of the transformer, the neutral is bonded to ground in the PDU. The neutral, equipment ground and isolated ground are all relatively similar impedance and connected to the same place (electrically) in the PDU. Other than lifting the conductors and toning them out, you probably can't see the result at the receptacle itself.
Remember that there should be essential 0 current on the grounds, so you could clamp the grounds of the branches and look for current, to see a problem downstream.

[ August 19, 2005, 01:57 PM: Message edited by: ron ]
 

catchtwentytwo

Senior Member
Re: ?Swapped? Neutral & Ground Condition

Ron,

I agree and use the clamp-on method after a visual locating the "white conductor in the wrong place". As you can imagine, having to correct this in data center environment isn't pleasant.

The journeyman who made the mistake was day dreaming and got fooled by the bar on insulated stand-offs. The PDU's manufacturer doesn't clearly identify it or the conductor feeding it. There's probably a small sticker that gets buried by branch circuit conductors.

I wonder why the code doesn't require Isolated Ground Bars to look unique, maybe orange stand offs? Given the misuse of isolated grounding, it would surely help.

Regards,
John

[ August 19, 2005, 04:08 PM: Message edited by: catchtwentytwo ]
 

ron

Senior Member
Re: ?Swapped? Neutral & Ground Condition

I would think the isolated ground bar in itself not bonded to the enclosure, would look unique enough to a trained person.
As IG circuits become more and more "not used", I would think more regulation will not happen.
 

catchtwentytwo

Senior Member
Re: ?Swapped? Neutral & Ground Condition

I think this picture might show where the problem began.


Disclaimer: This is panelboard in a factory wired PDU. Only the branch circuits were field installed. The OEM is responsible for the wiring not the manufacturer of the panelboard.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector
Re: ?Swapped? Neutral & Ground Condition

I wonder why the code doesn't require Isolated Ground Bars to look unique, maybe orange stand offs? Given the misuse of isolated grounding, it would surely help.
But the Code does require E. Grounding and Grounded conductors to be identified. My eyesight is failing, but I don't see such identification of conductors in the picture. Were they identified?
If not, doing so might have prevented this mistake.
 

catchtwentytwo

Senior Member
Re: ?Swapped? Neutral & Ground Condition

Exactly. However, is the manufacturer of the PDU held to the NEC?

BTW, your eyesight is fine, there is no identification on the conductors.

[ August 22, 2005, 03:40 PM: Message edited by: catchtwentytwo ]
 

Dnkldorf

Senior Member
Re: ?Swapped? Neutral & Ground Condition

And what is that?

2 wires under one lug at the nuetral lug?

Dnk...
 

catchtwentytwo

Senior Member
Re: ?Swapped? Neutral & Ground Condition

Actually there are three conductors under the lug.

In case anyone is wondering, the product was field evaluated by ETL and is labeled as such. It is comprised of a 480 volt static-transfer switch, 150 kva xmfr and four 42 circuit, 225 Panels.
 
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