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Q. What are the NEC requirements for installing conductors in parallel inside wireways?
See answer below.
A. The requirements for installing conductors in parallel inside wireways are found in Sec. 376.20. Where conductors are installed in parallel as permitted in Sec. 310.10(G), the parallel conductors must be installed in groups consisting of not more than one conductor per phase or neutral conductor to prevent current imbalance in the paralleled conductors due to inductive reactance (Figure).
Note: The purpose of having all parallel conductor sets within the same group is to prevent current imbalance in the paralleled conductors due to inductive reactance.
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