10mm Bonding

markythespark · Jan 11, 2011

Ok you get asked to quote for a consumer unit change, doing the site visit there is only a 4mm earth cable on the gas and water, but they are earthed. I always include a quote to upgrade to 10mm and explain why. If you have a customer who says that they can only afford to have the board changed and will upgrade the bonding later in the year? What does the BS7671 say about this?

malcolmsanford · Jan 11, 2011

Regulation 131.8 is the one that dictates that the bonding shall be adequate to the regs and then you go down to sections 544. and in the case of the 4mm^ then as reg 544.1.1 says the bonding must be half the size of the main earthnig conductor in a TN-S or a TT to a minimum of 6mm^ and in a PME be sized according to table 54.8 which for most domestic cases be 10mm^. So no matter which way you play this you should change the bonding.

In some case where you have a 6mm^ as in 16th edition regs it is somestimes thought that if you take a risk assement on the conductor and it as no sign of damame or burning, there could be a case to leave it and then mark it down as a deviation on the schedule of results. I'm not a great believer in this, unless it was virtually impossible to change it dues to conductor running under the floor which is covered by hugely expensive covering.

The 4mm^ though as to be changed. Perhaps you could work it into the price another way, but unless you can't you may have to walk away.