Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning PME system main earth and bonding conductor sizing, is answered by SELECT:
We have been asked to carry out an electrical installation to a design provided by a consulting engineer. The main supply authority cable is 300mm2 and is a PME system. The cable tails from the supply authority cutout are 185mm2. The consultant has indicated that the main earth is to be 95mm2 and the main bonding conductors are to be 25mm2.
We feel that the main earth and bonding conductors should be 50mm2 (based upon Clauses 542.3.1 and Table 54.8 of the Wiring Regulations). Can you advise?
Answer: From the information provided, it would appear that the main earthing conductor should be 95mm2 (unless calculation allows a smaller conductor), and the main bonding would then be a minimum of 35mm2. Both selections should be the responsibility of the installation designer.
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