Size of Ground Wiring

The size of the ground wire should be selected on the basis of the ground fault current. The ground fault current may be single phase to ground or two phases to ground where short circuit current will flow through the ground wire. The duration of the current flow should be considered to be not less than the tripping time of the short circuit protective device. As a thumb rule, the size of the ground conductor in a LV system should be able to carry the maximum short circuit current at that voltage level for a duration of one second. However, each country or region has their own local standards which should be adhered to.

The ground cabling has to be calculated by the fault conditions it could present and both local and national standards related to electrical power and ground wiring.

In the US it is NEC/NFPA/IEEE in other parts of the world it is generally IEC/ATEX/ISO, etc.

So first calculate the fault current to size the wire and the check what your local standards require as a minimum.

If you are in the USA refer to NEC Section 250 Table 250.122.

Otherwise refer to your local electrical code on equipment grounding requierments.

Please refer to your local electrical standards which dictate what sized earth conductor should be used for both safety and legal reasons.

Failure to do so could result in equipment damage or death.

Noudge79:

In the early '60s, prior to the publication of the Phil. Electrical Code (PEC), the NEC standards was the standards that was adapted and used as the guidelines by all local design engineers.

The 2nd edition of PEC was further modified to suit local applicable needs. The contents of which were all derived using a combination of the NEC and IEEE applicable standards.

It is advisable to get yourself a copy of the latest PEC edition for proper guidance on all local applications..

Vic