240.21.C. 4 (Outside Secondary Conductors)

[PJS3]

There is a debate between me and my colleagues regarding this section of the 2008 NEC.

The scenario here involves an outdoor 3 phase, delta-wye transformer with conductors located outdoors that feeds into an ATS which is also located outdoors. The debate is whether or not over-current protection is required for the secondary conductors.

Please join the discussion.

 

[charlie b]

Overcurrent protection is always required for any and all conductors. The thing the tap rules accomplishes is to allow us to, under specific circumstances, put the overcurrent protection device at the end of the run, instead of the beginning, where the conductors get their source of power. Take a look at 240.4, and then at the opening sentence of 240.21.

Welcome to the forum.

 

[PJS3]

Thank you for the welcome. I have been lurking for a while... lol.

Now, let me add to that question.

Would OCP be required between the transformer and the ATS or would a main circuit breaker in a panel/switchboard/switchgear/etc on the output of that ATS suffice (per code) as the OCP?

The real question here being, is the ATS considered part of the "secondary conductors" or do the secondary conductors "terminate" at the ATS?

 

[iwire]

Can I ask who controls the transformer and the secondary conductors?

Is it the utility or the owner of the property?

 

[charlie b]

Since the utility has its own rules, I will answer as though it were the owner who controls the transformer and the ATS. I believe you need an OCPD at or before the ATS. I see 240.21(C)(4)(2) as saying you can't terminate at the ATS, and then run more wires, before finally getting to an OCPD.

 

[PJS3]

Can I ask who controls the transformer and the secondary conductors?

Is it the utility or the owner of the property?

Well, there are three similar situations in the debate.

Two situations are utility transformers and one is an exterior mounted transformer feeding an exterior ATS.

 

[PJS3]

Well, there are three similar situations in the debate.

Two situations are utility transformers and one is an exterior mounted transformer feeding an exterior ATS.

Correction. No utility transformers. They are all customer owned transformers.