This Q & A is one of the thousands posted in our Technical Expertise area and answered by our Voltimum Experts.
I have an install involving 3 four core SWA of 240 mm2 feeding an MDP from a generator.The load is 1200 amps. When calculating the size of the protective conductor do I use Table 54.7 or the Aidabatic equation? three wire power cord
Would I consider sizing it to half of the combined area of the 3 (240mm2) size as in half of 720 mm2 or half of each 240mm2 . It is a TN-S from the generator. I do not wish to use the armour as the protective conductor.
What size should the earthing conductor be?
The size of an earthing conductor shall be in compliance with regulation 543.1.1. This requires either:
Calculation in accordance with regulation 543.1.3 and the adiabatic equation.
Selection in accordance with regulation 543.1.4 and Table 54.7.
The most typical method chosen is selection, in accordance with table 54.7 and the size selected is based on the cross-sectional area of the line conductor. For 25mm tails this results in a 16mm main earth. Using regulation 543.1.3 and the calculation method, the size of the protective conductor chosen is typically smaller than through selection. In the situation, you describe the calculation would need to be completed to determine whether the earthing conductor is adequate.
- Answered by an NICEIC Technical Expert
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