Earth cable size selection

Earth cable size selection is very important part of electrical engineering. Because it’s a protective measure of electrical system.

As per Bangladesh National Building Code (BNBC), the size of earth cable is discussed below.

The minimum Cross-sectional area (square mm) or rm of copper Earth Conduit Cable (ECC) is depend upon the size of associated phase cable.

  1. If the phase cable size is less than 16 rm or 16 mm2, that the corresponding earthing cable size will be same as the phase cable. For example, if the phase cable is 10 rm than the corresponding earthing cable will be 10 rm.
    If the phase cable is 6 rm, than earthing cable is 6 rm.
    But, earthing cable shouldn’t be below 4rm.
    For example if phase cable is 2.5 rm, then, earthing cable should be 4 rm.
  2. When phase cable size is 16 rm to less than 35 rm. Then, earthing cable will be 16 rm.
  3. If phase cable size is 35 rm or greater than 35 rm. Then earthing cable will be half of the associated phase cable.
    For example, if the phase cable is 50 rm then, the earth cable is 25 rm.

Reference: BNBC 2020, page no. 4598, table no. 8.1.26

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