Grounded Neutral

[brian john]

We have been working a job for 2 years with a grounded neutral issue. High current tripping the GFP at the 200 amp setting (where we found the gfp set). We could not get a long enough outages to isolate the problem and had to do the job in bits and pieces, worked on it again tonight (my guys are still there I left after isolating the major issue.)

Based on the high level of ground current I figured it had to be in the busway as branch circuits seldom contribute this high a level of ground current. This portion of the job had me worried for weeks as we had to take horizontal and vertical busway apart to isolate the sections.

We did locate over 100 branch circuits 6 months ago with grounded neutrals and are in the process of clearing these.
We also found the busway neutral shorted to ground this was also located 6 months ago.

What we found was when the busway was assembled the ground bus 1/8 copper was pinned against the neutral bus under the busway coupling insulator. Of course we did not locate this right away it was in the last coupling we took apart.

 

[iwire]

We did locate over 100 branch circuits 6 months ago with grounded neutrals

What is up with that?????????

Was someone trying to ground the neutral?

Over a 100 out of how many total?

it was in the last coupling we took apart.

Of course, why would you take apart more once you found the problem. :grin:

 

[Pierre C Belarge]

Of late we have been asking the contractors to be on the site for inspections that have panels. We want the panels opened for a looksee.
Since, we have found that the bonding and grounding issues are mixed up and at about 80% of the time, the MBJ is missing at the service or the neutral to ground connection is made at the subpanels.

So, Bryan's find does not surprise me at all.

 

[iwire]

So, Bryan's find does not surprise me at all.

It surprise the heck out of me, there is no excuse for over a 100 branch circuits to have grounded neutrals.

 

[Fulthrotl]

Based on the high level of ground current I figured it had to be in the busway as branch circuits seldom contribute this high a level of ground current. This portion of the job had me worried for weeks as we had to take horizontal and vertical busway apart to isolate the sections.

We did locate over 100 branch circuits 6 months ago with grounded neutrals and are in the process of clearing these.
We also found the busway neutral shorted to ground this was also located 6 months ago.

What we found was when the busway was assembled the ground bus 1/8 copper was pinned against the neutral bus under the busway coupling insulator. Of course we did not locate this right away it was in the last coupling we took apart.

how appropriate that an easter egg hunt ends on this weekend....
congratulations.

100 grounded neutrals? ick. what are you using to look for the grounding
points with? suretest 61-155? it has the ability to tell if the grounding
point is within 15' UPSTREAM of the connecton point... that might prove
helpful.

"pinned"? was it intentionally connected, or just sprung and forced into
the wrong slot when the bus was assembled?

when i've built bus duct, i megger every connection, after it's torqued...
before adding the next section....:smile:
and take a sharpie and put my initials and the date at each connection.
couple of the foremen i've worked for when doing this, have given me
poo about "wasting time"..... but when hughes el segundo was being built
in 1982, i got stuck on the "bus duct repair crew". however, in that case,
the bus duct was deliberately sabotaged.... elevates wasting time to a
whole new level.....

 

[brian john]

What is up with that?????????

Was someone trying to ground the neutral?

Over a 100 out of how many total?

This was a 10 story building two risers 30 panels (480/277) But my guys told be most of the neutrals were grounded in VAVs, taped green and terminated as a EGC. Some were on individual suites security systems same issue. The rest maybe 15-20 were lighting branch circuits where the neutral was shorted in the MC connector, in the switch (2" screw), MC cut with hacksaw and neutral was cut and shorted and other typical locations for a short.

The 10-15 is typical for a 10-12 story high rise.

 

[roger]

This was a 10 story building two risers 30 panels (480/277) But my guys told be most of the neutrals were grounded in VAVs, taped green and terminated as a EGC.

Sounds like the Mechanical contractor was making up the VAV's.



Roger

 

[brian john]

when i've built bus duct, i megger every connection, after it's torqued...
before adding the next section....:smile:

With busway we recommended meggering each section as it comes off the truck, each section as it goes in then megger the installed completed portion. All spot test quick go no go.

Then upon completion megger per manufacture and industry standards.