ECN Forum Forums Technical Discussion Electrical Theory and Applications SDS Xo conductor to the disconnecting means

On a Separated Derived System (SDS) of secondary voltage of 480/277 and the Xo terminal is bonded to the case and to a ground rod within the transformer pad opening, is a grounded (Xo) conductor required to be installed to the remote disconnecting means as 240.24(B) [ that is to be corrected to 250.24(B)] requires for services ?

[This message has been edited by Gwz (edited 01-15-2003).]

Gwz,

Yes (if no direct means of ground bonding - like overhead feeds or PVC raceways).

The Secondary side of the SDS' Transformer needs to have some solid means of connecting the Disconnecting means (or first panel) to the Grounded Conductor and the Terminal of the Transformer which is Ground Bonded.
This is normally done by bringing the Grounded Conductor to the first panel / disconnect, and if not needed for load side circuits, simply terminates to the enclosure.

Exceptions here will be if the Secondary feeders are run in a metallic raceway / conduit, which creates a complete Ground path between the Transformer's Enclosure and the first panel / disconnect (Conduit is EGC).
Also, if any EGC is installed with the feeders, which is bonded to the GES and Transformer enclosure - plus bonded to the enclosure of the first panel / disconnect.

If the above scenario(s) are done, the system is correctly bonded and does not require the Grounded Conductor to be run to the first panel / disconnect.

Wait for some input / comments from the more "Code Fluent" Members before figuring this to be "Okee - Dokee - Pokee"

Members: Jump in here and let me know what I have listed, if not compliant to the good book (NEC)!

Scott s.e.t.

If a solid conductive path exists (i.e. metallic conduit) between the transformer and the first disconnect, then the bonding can be done in only one place. Bonding in both places would cause a parallel ground path.

If there is no direct ground connection (i.e. direct burial conductors) between the transformer and the disconnect then bonding must be done in both locations. (In this case the transformer enclosure is being grounded for safety purposes only, the primary path for fault clearing would be at the disconnect.)