When the concentric neutral in this cable is grounded at both ends, there is a possibility of circulating currents in the neutral. This can happen either due to unbalanced currents in the 3-phases, due to magnetic induction from the long run, or due to a short circuit involving a line to ground fault. In any case, this current carrying neutral constitutes the fourth cable in the set of three cables inside a conduit. Derating the cable for this additional wire is necessary. Sometimes the concentric neutral conductor on top of the insulation is not required, typically when supplying power to an industrial load (which predominantly contains three phase loads). There are cables that have a tape shield over the insulation in place of a concentric neutral conductor. These cables cost less to manufacture. Call us at Northern Power for any questions that you may have.
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