Branch Circuit Tapped Before Main Breaker

I have seen a similar arrangement in an electrical utility company where many of the 13.8kV breakers fed multiple feeders which supplied 4160V and 480V load centers throughout the plant.

In some instances two or more feeders were terminated at the load side of a single breaker. Other times, a single feeder terminated at the breaker went to a splice box where it was spliced to multiple feeders. The 13.8 kV breakers provided only feeder fault protection and not cable or transformer overcurrent protection. Transformer protection was provided only by the low side circuit breakers. This obviously provided no protection for a transformer overload caused by shorted turns which was probably considered to be a low probability event.

The intent of the scheme was economy and reliability and not equipment protection. It was probably based on risk/consequences of an overload versus a fault.

I don't know if this configuration will be addressed by any code. It may be more of an insurance concern than a safety issue.

NEC Section 240 Tapped Conductors.

As another poster has already stated Section 240, more specifically 240.21(B)(1), of the U.S. National Electric Code (NEC) covers this situation.

Section 240.21(A) through (G) contains permissible rules for under-protected "tapped conductors." Part (B) of Section 240.21 is broken down according to lengths of conductors from taps. These regulations are commonly referred to as "NEC tap distance rules."

In Australia, (your avitar doesn't say where you are) to our Wiring Rules, the only time this is permissible is for a feed like this is to fire fighting equipment. This is so when the board is taken off at its main isolator the fire equipment is still energised. No other equipment has this permission.

To all responses,

Thanks very much, I appreciated the insights - and the pointer to NEC article 240 gives me my homework assignment.