Secondary Transformer Feeder Taps & Circuit Protection NEC240-21(c4) 1

[JFG]

Within a utility substation, 40MW of distributed generation is presently being installed. A station service transformer for this generator addition (3-phase, 12,470-480V, 1500KVA, wye primary and delta secondary) has three individual feeder loads tapped directly from the secondary to power multiple loads consisting of two motor control centers (MCCs) and one motor starter. The source end at the transformer for each of the these three ungrounded outdoor circuits (each less than 25 feet in length) are without overcurrent protection, but each has, at the receiving end, a circuit breaker rated for the cable ampacity of each circuit. Two of the terminations are indoors and the third terminates within an outside motor starter cabinet. The primary for the transformer is protected with fused disconnect switches. This design is based on 1999 NEC 240-21: "Location in Circuit" with exception of (c)(4): "Outside Secondary Conductors" used. With this said, the site electrical inspector is interpreting the NEC code as to allow only one unprotected tap at the feeder source rather than three, which we in our office believe to be in error. Unless we are interpretating the code incorrectly, it is desired to receive through this forum supportive responses that what has been designed for the site is correct as per the NEC. A one-line drawing can be faxed for reference to those interested. Thank you in advance for any help or assistance you can provide in this matter.

Sincerely,
JFG

 

[maurert]

JFG,
Perhaps the inspector is looking at Article 240-21 (c) Condition (3). Article 240-21(c) …all four conditions must be met:
Condition 3: The tap conductors terminate in a single circuit breaker or single set of fuses…

I read it as your tap must terminate in a single overcurrent-protective device and then it can be distributed from there. Unless I’m missing something it sounds like you need a single, fused disconnect between your transformer and your three sets of feeders.

Good luck,
MaurerT

 

[REDDOG]

Only the electrical inspecter can interpret the code.
Mauret is correct you must protect the conductors at thier
source of supply. You have a seperatley derived system and must treat this a "a service"" and ground and protect accordingly.