Parallel current okay?

[Steelhead]

In the installation of the SBJ at the first disconnecting means as allowed in 250.30 (A)(1)(b) a parallel path for neutral current is created if metallic conduit is used as the connecting raceway between the transformer and the first disconnecting means. Is this considered acceptable?

 

[electrofelon]

In the installation of the SBJ at the first disconnecting means as allowed in 250.30 (A)(1)(b) a parallel path for neutral current is created if metallic conduit is used as the connecting raceway between the transformer and the first disconnecting means. Is this considered acceptable?

In this situation there is not a parallel path. In this case there would NOT be a neutral ground bond at the transformer. Just note that you need a bonding jumper from the case of the transformer to the derived system disconnect if you do it this way (there is a good graphic on this in the handbook). You can bond at both places if the connecting raceway is non-metallic.

 

[texie]

In the installation of the SBJ at the first disconnecting means as allowed in 250.30 (A)(1)(b) a parallel path for neutral current is created if metallic conduit is used as the connecting raceway between the transformer and the first disconnecting means. Is this considered acceptable?

There will not be a parallel neutral path if you are bonding the neutral only at at the first disconnect. When bonding at the first disco. you can't also bond the X0 in the transformer. The SBJ is for bonding the transformer case.
Some like to bond at the transformer X0, and that's OK, but then you do not bond the neutral at the disconnect. But you still need the SBJ, in this case from X0 to the EG bar in the disconnect.
Either way, there is no parallel neutral path.

 

[Steelhead]

Whoops, I guess I didnt think that question all the way thru. You guys are absolutely right. I cant believe I didnt see that. I should know better. I confused myself when I was reading about the supply side jumper. Sorry. Thanks for the correction!

 

[electrofelon]

Note that in the 2014 NEC, on odd days you have to bond at the first disconnect means and on even days you have to do the bond at the transformer. Inspectors will be requiring a photo with a time/date stamp.

 

[texie]

Whoops, I guess I didnt think that question all the way thru. You guys are absolutely right. I cant believe I didnt see that. I should know better. I confused myself when I was reading about the supply side jumper. Sorry. Thanks for the correction!

We all have our moments.

 

[Smart $]

In this situation there is not a parallel path. In this case there would NOT be a neutral ground bond at the transformer. Just note that you need a bonding jumper from the case of the transformer to the derived system disconnect if you do it this way (there is a good graphic on this in the handbook). You can bond at both places if the connecting raceway is non-metallic.

While Code still has that text, in the 2011 edition a supply-side bonding jumper is required... so installing a system bonding jumper in both the transformer enclosure and the first disconnecting means would be a violation, regardless of raceway type.