Generator Set Neutral Earthing Cable Size

[azri]

Hello to all of you. Happy new year 2013. I'm azri, just joining this forum today after found it after google for some other related electrical stuff.

This have been my recent problem which is to determine the cable size for grounding the generator set neutral to earth chamber. I use BS7430 (not sure if used in this forum since this is US forum) and BS7671, but I couldn't find any where stating the calculation or any rules to determine the size.

I heard from my clique that the thumb rule is genset neutral cable to ground is size up to quarter of the output current.

Is that true? Is there anywhere I can refer any technical specification in any standard either IEC, BS or any other standard?

Thank a lot.

 

[Dennis Alwon]

We have some members who may use the British system or IEC but most of us use the NEC and we have a Table- 250.66 for sizing the grounding electrode- I think that may be what you are looking for. Hopefully someone will respond. I think the IEC is similar if not the same as the NEC

 

[azri]

We have some members who may use the British system or IEC but most of us use the NEC and we have a Table- 250.66 for sizing the grounding electrode- I think that may be what you are looking for. Hopefully someone will respond. I think the IEC is similar if not the same as the NEC

thanks dennis. but the one i'm searching for is not the grounding electrode sizing. Mostly that electrode I think is 16mm2 for most application. The one I'm concerned is the cable from genset neutral point, all the way to the earthing terminal or earthing electrode.

This is because by BS standard, for phase cable size more than 35mm2, the neutral cable is always the same size as phase cable. but for earthing cable from earth busbar usually just 25mm x 3mm copper tape. this left me confuse for two days.

IEC is widely use in malaysia but NEC also acceptable. I just want any reference to back up my knowledge, not just baseless thought. it good to know it so that you can be confident with your design.