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current inbalance

current inbalance

current inbalance

Is there a section in the code that pertains to the maximum amount of current inbalance allowed for a three phase 4 wire 277/480 volt 1000 amp service entrance conductors? If so where can it be found or is it just a certain percentage allowed?

  I have a situation where parallel conductors have been tapped but they did not incorporate all three conductors of each phase & neutral when they tapped the wires. In my opinion this is illeagle since you will be creating and inbalance on the conductors on each phase thus creating inductance that will eventually burn up the wiring.

RE: current inbalance

I don't believe there is a specific limit.  The NEC says that the loads should balanced.

Taps are covered in the NEC and are permitted if the rules are met.

I don't think the inductance is going to have much heating effect.  

David Castor

RE: current inbalance

The NEC requires the wiring to be able to supply the unbalance, not the other way around. See 220.61.  

RE: current inbalance

There is no limit to imbalance; however, each conductor must have the ampacity and overcurrent protection for the load it will carry (Article 240.4).  The other code concern for imbalance is in Article 392.8 (D) where it is possible that currents may not be balanced in paralleled sets if their installation is not grouped properly.  Finally, the code recognizes that imbalance in loads will have an effect on a feeder or service neutral conductor (Article 220.61).

So, as long as the conductors are properly installed and protected from overcurrent, there is no restrictions on imbalance.  From an engineering point of view, balance is good practice to allow economy of conductors, transformers, and devices, but some imbalance is nearly always present to some degree, and is frequently unavoidable.

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