Open Neutral??

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jimvango

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Fort Collins, CO. USA
Called to check out electrical problems in outlets in commercial office setting. Occupant reports hearing a very loud bang and computer and various equipment plugged into the outlet and plug strip quit - hot electrical smell throughout area. They unplugged all the equipment from other outlets in three offices that seemed to be affected. My exam at initial outlet with woodhead tester has all 3 indicator lights lit. Opening up the outlet led to finding the hot and neutral each showing 120V to ground on a wiggee. Copper circuit conductors are fed in EMT from a 3 phase 120/208V panel. No breakers tripped and all connections tight. Three circuits sharing same neutral feed the offices in question. Above ceiling junction boxes reveal tight connections for the most part. Neutral conductors discolored and a little loose but they were all still together under the wing nut. Additional outlets and j boxes opened and no other problems found. All neutrals were tried together in the boxes with a separate pigtail connected to the outlets. Everything was put back together and all appears to be working well. Power supply for the computer was fried and a plug strip and keurig coffee maker plugged in on a different phase circuit in the next room shot as well. Does this sound like an open neutral occurrence? Any thoughts are much appreciated. Thanks.
 
Three circuits sharing same neutral feed the offices in question.
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180 VA per yoke came to mind

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Here's a heavy conversation(link follows) that brings up my point of 180 VA on a yoke and a statement on the subject #57 states the same answer as the above graphic. MH Forum

What I would do would be to run three neurtrals home and try to balance the usuage between the three offices. Replace the browned neutral wire, and bill accordingly.
 
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jimvango said:
Opening up the outlet led to finding the hot and neutral each showing 120V to ground on a wiggee. Does this sound like an open neutral occurrence? Any thoughts are much appreciated. Thanks.
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Anytime you can measure 120V neutral to ground would suggest an open neutral.

Somewhere upstream (main) the neutral will be bonded to the ground so you should not measure anything.
 
jimvango said:
Neutral conductors discolored and a little loose but they were all still together under the wing nut.
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Just looking at a tap can often fool you into thinking it's a good connection. When you tighten a wire nut you would need to go back an see if you are still reading that 120 V neutral to ground. If this voltage were to magically disappear you would know that you found your loose connection.

The best idea would be to take this tap appart and strip off the ends and make a new splice because the old ends may have arced ( not the best connection).
 
Probably is Open Neutral

Probably is Open Neutral

Hello all - Thanks for the replies. The panel is on the load side of a 277/480V transformer and there is a bonding screw in place bonding the neutral to ground in the panel. Running additional neutrals is a difficult option as the panel is on the third floor and these offices begin 100' away on the second floor. All areas are occupied. Capacity fill of the conduit won't allow this option either - so I'd have to run additional conduit and separate out the circuits. There are only 5 or 6 duplex receptacles on each circuit - but with all the modern conveniences several of the outlets have plug strips connected to them. Thank goodness there are no daisy-chained plug strips with one plugged into another. I regret that I did not check voltage between the hot and neutral on the initial outlet - but think that I would have found no voltage reading between the two. Everything is working now so I suppose the problem must have been in the j box where the neutral was a bit loose. I certainly don't want the situation to occur again.
 
You mentioned discolored wires and slightly loose connection in a J-box. i would bet that was your problem.

Only takes a second for the nuetral to go away and fry the things plugged in.
Yes there could be another location ,
 
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