Neutral bonding sub panels/steel building

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jrob

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Just had a question on bonding the neutral of subpanels. I know in the codebook it says you are allowed to bond the neutral of a subpanel if there is no mechanical ground run with the feeders, and there aren't any metal pipes running between locations. On the site that I'm working on I've had to do this temporarily a few times where there was no mechanical ground and no pipes between locations. Now I've come across a steel building with multiple exterior mounted subpanels and two are missing mechanical grounds. It's impossible at the moment to run new feeders, and I'm not sure if I feel comfortable with bonding the neutrals in this situation. I also have two unrelated free standing panels without mechanical grounds. One panel feeds the other, and I'm not sure about bonding the neutrals in this situation either. I have alot of concerns about objectionable neutral current in these particualr situations, but management feels it won't be an issue. All comments welcome. I want to make sure this already bad installation isn't made worse.
 
Jrob,

Easy fix.
Install the Ground Rods and check the wiring.

It is my understanding that in sub-panels
(1) the Neutral is Not Grounded.
(2) an EGC is to be pulled from the primary panel.
(3) the sub-panel is bonded with the EGC and grounded to GEC to a ground rod.

Check this out.
 
jrob said:
............. I have alot of concerns about objectionable neutral current in these particualr situations, but management feels it won't be an issue. All comments welcome. I want to make sure this already bad installation isn't made worse.
Click to expand...

Draw up a letter for management to sign that clearly spells out the dangers involved and that points out clearly that you are not charged with the authority to waive any safety rules in legally referenced standards (neither is management) and long before anyone is dumb enough to sign off on this type of letter, someone with at least half a brain will step up to the plate and cause the proper remedial action to take place. :)
 
jrob said:
Yes, there are two seperate feeders. This whole building is messed up.
Click to expand...
Rule: do not bond a neutral (grounded conductor) at a sub panel, see NEC 2008?s 250.4(A)(5), 250.142(B), & 250.32(B).

Exception: the neutral can be bonded in some existing installations when all of the criteria of 250.32(B)?s Exception is met.

Reason: current will travel ALL available paths returning to it?s source.

The real danger of a duel fed building is cross tying circuitry between them causing back feeds, and of course too many multiple disconnects for emergency reasons.
 
Yikes !!! I'm not sure what I would do ,.. I can tell you I'd be pondering walking away .. I can only imagine what the rest of the wiring is like...

Also the language used in regard to management ... red flag .. a big red flag ..

...."but management feels it won't be an issue...."
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thats nice ,..perhaps they can do the work and assume the liability then
 
jrob said:
?I have alot of concerns about objectionable neutral current in these particualr situations, but management feels it won't be an issue. All comments welcome. I want to make sure this already bad installation isn't made worse.
Click to expand...

Most often an appropriate reply to management like this is something like:

The NEC is not something to avoid or get around. It has been authored for over a century, regarding the use of electricity, for only two reasons; personal and property protection. For these reasons it is not wise to intentionally avoid the NEC.

I often here statements from non electricians ?well it?s been working? or ?why does it work then!?? Both of these assertions are rationalizing to avoid correction. The real problem with these rationales? is they are questioning what is ?correct?. In their eyes correct is most often what works. In our eyes correct is qualified by the NEC.

Your concerns are legit and if the hierarchy above you does not understand why, it may not even be your role to teach them, so just simply expose the violations and risks to them. In your example if any 120V circuitry is used current will be flowing on all conductive parts returning to their sources. Because of this electrocution is likely as well as functionality of equipment. You don?t need to explain why this may not have happened yet; it is simply why these codes exist.
 
How are the feeders run?

How are the feeders run?

jrob said:
Just had a question on bonding the neutral of sub panels. I know in the code book it says you are allowed to bond the neutral of a sub panel if there is no mechanical ground run with the feeders, and there aren't any metal pipes running between locations. On the site that I'm working on I've had to do this temporarily a few times where there was no mechanical ground and no pipes between locations. Now I've come across a steel building with multiple exterior mounted sub panels and two are missing mechanical grounds. It's impossible at the moment to run new feeders, and I'm not sure if I feel comfortable with bonding the neutrals in this situation. I also have two unrelated free standing panels without mechanical grounds. One panel feeds the other, and I'm not sure about bonding the neutrals in this situation either. I have a lot of concerns about objectionable neutral current in these particular situations, but management feels it won't be an issue. All comments welcome. I want to make sure this already bad installation isn't made worse.
Click to expand...

What exactly do you mean by "mechanical ground"?

If the feeders are run in metallic raceway the correction may be to tighten up some joints, install a bonding bushing or two, and remove the bonding connections between the feeder supplied panel cabinets and the neutral conductors.
 
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