OCPD for Parallel Conductor

[hill900505]

Hey guys,
I have a question about applying overcurrent protection device for parallel conductors. Say, is an 800Amps breaker good for protecting two 500kcmil conductors (Will not consider derate, the ampacity for 500kcmil copper conductor is 380Amp). To me, this breaker can not do it because if one of the parallel conductor is damaged, this 800amp breaker can not protect one 500kcmil conductor, is this correct?
Thanks everyone.

 

[GoldDigger]

Regardless of the possibilities and probabilities of damage to only one of a set of parallel conductors, the NEC considers the parallel run to be equivalent to a single conductor with the same current carrying capacity and considers it to be protected by a single overcurrent device.

With a single conductor, you can pose the question of whether it is adequately protected if a poorly made termination has a high resistance or several of the strands of a multistrand cable should break.

The answer is the same in that case: as long as the breaker protects a cable which, in good condition, is adequate to carry the current, it is acceptable under the NEC.
What the NEC does NOT allow, AFAIK, is to put individual OCPD on each member of a parallel set.

 

[iwire]

Hey guys,
I have a question about applying overcurrent protection device for parallel conductors. Say, is an 800Amps breaker good for protecting two 500kcmil conductors (Will not consider derate, the ampacity for 500kcmil copper conductor is 380Amp). To me, this breaker can not do it because if one of the parallel conductor is damaged, this 800amp breaker can not protect one 500kcmil conductor, is this correct?
Thanks everyone.

Do you mean one conductor faults to ground?

If so that breaker will still trip just like an 8 AWG equipment grounding conductor can trip a 100 amp breaker.

About the only way to overload one conductor of a parallel set is if others of the same set become disconnected which would be rare enough to be unlikely.

By the way, two 500 coppers can be protected by a 800 amp breaker but you could only load them to about 760 amps.

To get a full 800 amps you need two 600 copper.