Subpanel bonding (3-phase mains) question

Is it never allowed (US National Electrical Code) to bond the ground bus bar to the neutral bus bar?

I opened a subpanel and found that both the ground bus bar and cabinet were bonded to the neutral bus bar.

Is this allowed under any circumstance?

This is a "Y" 208/120 configuration utilizing 5 conductors in an industrial building.

Thanks.

No, according to the NEC it is not allowed in a subpanel at all.

No. As long as it is a sub-panel. Not to be confused with a seperately-derived system(after a transformer).

RE

With the exception of feeders to separate buildings under previous editions of the US NEC it is not permissible.

-- Tom Horne

Single building, not large (2000 sq ft?) one service entrance, one main panel, 3 or 4 subpanels.

It looks like this bond needs to be broken...

Thanks, Mike (OP)

When you say 'sub-panel', it may be confusing. A step-down transformer fed from the service entrance, that in turn feeds 208/120 to a panel is not a sub-panel. In that case the first panel off the transformer is not a usual 'sub-panel' but a fed from a separately derived source (the transformer).

You mentioned 208/120 in an 'industrial building', so I think the building service is not 208/120 directly but may be a higher voltage and you have a step-down transformer inside the building.

In that case, the ground/neutral *should* be bonded in the first panel after the transformer.

Now, any other panels fed from the first panel after the step-down transformer are true 'sub-panels' and thus should not have the ground and neutral bonded.

So just to be clear here, are you talking about a true 'sub-panel', or the first panel downstream of a step-down transformer?

daestrom