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Subject - 208/120 Neutral Hookup
JimmyDee This is a picture from the Electrical Matters Forum and found this in a link that David Nix had in there from the Residential section of this forum. I have a question about the following diagram:

The hook-up on the left shows no neutral connection at the center tap of the transformer but shows it at the grounding point/bar in the disconnect. Is this legal? I always thought it would have to be hooked up like the digram on the right.
Jim
iwire The code allows either or both places.

If for some reason you did go with both there can not be any metallic paths between the two bonded points.

A place that it is done in both places is any service.

The power company transformer and the service disconnect are both bonded.

quote:
250.30(A)(1) Bonding Jumper. A bonding jumper in compliance with 250.28(A) through (D) that is sized for the derived phase conductors shall be used to connect the equipment grounding conductors of the separately derived system to the grounded conductor. Except as permitted by 250.24(A)(3), this connection shall be made at any point on the separately derived system from the source to the first system disconnecting means or over current device, or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices. The point of connection shall be the same as the grounding electrode conductor as required in 250.30(A)(2).

Exception No. 1: A bonding jumper at both the source and the first disconnecting means shall be permitted where doing so does not establish a parallel path for the grounded circuit conductor. Where a grounded conductor is used in this manner, it shall not be smaller than the size specified for the bonding jumper but shall not be required to be larger than the ungrounded conductor(s). For the purposes of this exception, connection through the earth shall not be considered as providing a parallel path.
Scott Vickrey Sounds good, Let me ask about the conduit connecting the transformer to the secondary's first disconnect. If it's flexible metal conduit. What are the bonding requirements for each method?
iwire I do not know of any special bonding requirements for flex on the secondary side.

I would never use the flex as the EGC.