Bonding neutral to can question.

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220/221

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AZ
The neutral and grounds only tie together at the service.

This is electrical 101, right?

Are there any exceptions that may apply?

10 story residential building about 7 years old. All conduit and MC cable.

200 amp single phase, main lug only, 4 wire THWN feed thru PVC, in each unit.

I was visually inspecting the panel (after a short in a kitchen recep tripped a breaker) and found that the neutral bus was bonded, with the factory screw, to the can. I was about to remove it but thought maybe I was missing something.

This is electrical 101, right?

I didn't look at the service section but I know that there is a fused/breakered disco somewhere.......probably downstairs. I assumethat that would be the service and the neutrals would have to be isolated after that point.

I wanted to check here and make sure I wasn't missing something.
 
IMO, you did not miss anything. Panels should not be bonded if they are not at the main disco. As you said, elec 101 :roll:. Its a good idea to look at the mains and if you can, other panels, this may be in more than one place. You could correct a mistake and possibly make a little extra $ :D.

As far as I know, the only time you rebond the grounded conductor to the can is after a xfrmr or if you are in the 2005 NEC at 250.32 for seperate buildings. (This goes away in '08)
 
Thanks. I was 99% sure that there were no exceptions. After a few more replies I will be @ 100%.

I am going to take some pics and write up a proposal to inspect/correct the entire building.
 
Take a look at
250.24(A)(4) Load-Side Grounding Connections.

Reference the FPN that directly follows this section number, as it references the other sections in 250 that permit the neutral-ground bond.

BTW: Your grounding 101 is very good
 
220/221 said:
Thanks. I was 99% sure that there were no exceptions. After a few more replies I will be @ 100%.

I am going to take some pics and write up a proposal to inspect/correct the entire building.
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Make sure you explain the dangers of exposed metal parts carrying current.

The money they pay you is much better spent than the impending lawsuit:D
 
This is a very common installation error. Many electricians believe that since the manufacturer provided the bonding screw they have to install it.
 
Do get a look at the main disconnect. It's probably just what we all seem to be thinking ("Hey, it came with a bonding screw."), but you never know what else you might find.:roll:
 
You are 99.999% correct but i would be very carefull about removing it. Yes it is wrong to be there but if the installer goofed here what else might be wrong. You could end up with no neutral or ground. Take it very slow and inspect everything on this service. Then with all breakers off remove it. Hopefully all you have here was a 1st year helper that wasnt being watched and an inspector that simply didnt look at each and every panel. It very much so needs fixed.
 
Jim W in Tampa said:
You could end up with no neutral or ground. Take it very slow and inspect everything on this service. Then with all breakers off remove it.
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Then do voltage tests between the two, including with a load or few restored, and maybe even against a known ground if you finda discrepancy.
 
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