First sub-panel wiring date???

[David C. Argabright]

Were 240 volt sub-panels EVER allowed to be connected with only three wire feeds? I know there are a very few exceptions but when were the four wire systems FIRST required by the NEC.

[Jim Katen]

Originally posted by David C. Argabright

Were 240 volt sub-panels EVER allowed to be connected with only three wire feeds? I know there are a very few exceptions but when were the four wire systems FIRST required by the NEC.

Certainly not since 1947 - that's my earliest NEC edition. It might have been allowed before that, but I doubt it. The early codes were quite clear about the need to eliminate objectionable current from grounding conductors.

From the 1947 NEC:

2523. Grounding Conditions for Alternating-Current Systems. Blah, blah, blah. . . No connection to a grounding electrode shall be made to the grounded circuit conductor on the load side of the service disconnecting means except as provided for in section 2524.

Section 2524 deals with separate buildings on the same service.

- Jim Katen, Oregon

[Brian G]

Douglas Hansen says this runs back to at least the 1920's. It's not new at all.

Brian G.

Neither Is Ignoring the Rules []

[jon_ran]

Originally posted by David C. Argabright

Were 240 volt sub-panels EVER allowed to be connected with only three wire feeds? I know there are a very few exceptions but when were the four wire systems FIRST required by the NEC.

Yes they are allowed. If one of the following applies...

1. The panels are connected with a complete conductive path by solid metalic conduit to provide the ground. The metal conduit becomes the 4th conductor.

2. If the panels are not connected with conductive conduit, a grounding source should be provided separate of the grounding utilized by the first service panel. (ie. a detached garage with no conductive grounding paths back to the main service can utilize a grounding rod)

[Jim Katen]

Originally posted by jon_ran

Originally posted by David C. Argabright

Were 240 volt sub-panels EVER allowed to be connected with only three wire feeds? I know there are a very few exceptions but when were the four wire systems FIRST required by the NEC.

Yes they are allowed. If one of the following applies...

1. The panels are connected with a complete conductive path by solid metalic conduit to provide the ground. The metal conduit becomes the 4th conductor.

Good point.

2. If the panels are not connected with conductive conduit, a grounding source should be provided separate of the grounding utilized by the first service panel. (ie. a detached garage with no conductive grounding paths back to the main service can utilize a grounding rod)

Yes, that's true. But the presence or absence of the ground rod isn't related to whether or not the outbuiding is fed by three or four conductors. The outbuilding should have a grounding electrode system regardless of whether or not the grounding and grounded conductors are bonded.

- Jim Katen, Oregon