- Reaction score
- 2,853
This tallies with guidance in best practice guides 1 and 4. If the main bonding conductors are at least 6mm, and no thermal damage present, then it's not considered potentially dangerous.Thanks for all your replies so far. I did use the adiabatic equation to calculate the earthing conductor size, and I agree that this calculation is somewhat irrelevant when you consider the BS7671 regulations on PME main and bonding cable sizes. (132.16 etc.) Which give a value of 10mm csa for both.
Now this particular installation is a new consumer unit only. The property was wired according to the 14th edition and the requirements then were for the bonding cables to be at 6mm csa according to table D2M. According to the NICEIC, there is an allowance, when working on existing installations wired to a previous edition of the regs, for the bonding cables to be left as they are and not increased to 10mm. This is provided that a) continuity is verified and at an acceptably low value (in this case both are <0.05 Ohms) and b) there is no sign of thermal damage to the cable. There is no sign of overheating of the bonding cables in this instance.
So basically the existing 6mm bonds can be kept in place, with a note on the EIC to confirm that they are only 6mm but have not been subject to thermal damage. This avoids a large amount of disruption running new 10mm cables which aren't in fact needed.
However, if they are less than 6mm, then it's considered a C2, potentially dangerous. This is a problem, as in your OP you said the bonding conductors are only 4mm.