Objectionable current

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Leespark57

Senior Member
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Boston, MA, USA
A colleague and I were having a discussion about using a metallic raceway between a meter socket and a main breaker panel. We both agree bonding bushings are required due to the fact there are service entrance conductors in the raceway. However, for example, a standard 200 amp meter socket has the neutral lug bonded to the frame of the enclosure of that meter socket. The 200 amp main panel also has the neutral connection bonded to the enclosure with the main bonding jumper. Therefore, using a metal raceway creates a parallel path for the neutral between the meter and the panel. Thus a percentage of the neutral current will be flowing through the raceway.

Isn't this considered objectionable current and a violation of 250.6?
 
It's not a violation because it's not possible to prevent it when using a metal raceway. It's just something that has been accepted for a long time.
 
Technically speaking, there is no grounding conductor on the line side of the main disco, and the meter is seen by the NEC as a lump in the service cable. On the line side, the enclosures are looked at as part of the neutral conductor, so yes, the nipple will carry some current a if it was the spiral-wrapped neutral inside SE cable.

You only need one bonding bushing, by the way, and it's just to assure that the nipple does behave as if it was part of the neutral conductor. In fact, if the nipple is screwed into a threaded hub that is bolted to its enclosure, you don't even need one bushing nor its jumper; the enclosure's own bonding jumper will suffice.
 
With TN-C-S there will always be objectionable current at some point at the service or even the building itself.
 
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