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Bonding maximum resistance

Ricki Carter

Apprentice electrician here and I would really like help on clearing up a confusion about bonding. I'm coming towards the end of my apprenticeship and have always been told that the maximum reading for a bonding to water and gas is 0.05ohms. I have been fine with this for the last 2 years but have this weekend been confused as GN3 and 7671 doesn't actually state this. Any help clearing this up you be amazing thank you. I know why we bond and what it is used for it's just where the 0.05 comes from. 

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    Supplementary protective bonding .... It has a criterion to achieve a theoretical maximum touch potential, of either 50 V (if applied under Section 415) or 25 v (if applied under Section 710 or APEA Blue Book for filling stations)  for the expected fault current.

    Isn't it based on the current required to open the protective device within 5s, rather than the expected fault current - which could (often should) be significantly larger? Larger currents may produce larger touch voltages (exceeding 50V or 25V), but balanced with reduced disconnection times.

      - Andy.

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    Supplementary protective bonding .... It has a criterion to achieve a theoretical maximum touch potential, of either 50 V (if applied under Section 415) or 25 v (if applied under Section 710 or APEA Blue Book for filling stations)  for the expected fault current.

    Isn't it based on the current required to open the protective device within 5s, rather than the expected fault current - which could (often should) be significantly larger? Larger currents may produce larger touch voltages (exceeding 50V or 25V), but balanced with reduced disconnection times.

      - Andy.

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