In case，laying multiple cable in the same phase conditions，and choosing the cable as the current flowing evenly，there is a possibility of overheating of cable，if not afford to allowable current of the cable. It is because impedance difference due to phase unbalance ，the current does not flow evenly，Impedance difference due to phase unbalance for laying multiple cable in the same phase，has not been sufficiently recognized .In planning，it is necessary to pay attention enough about the arrangement of the cable phase.

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