consumer unit change with undersized main bonding.

[payney 0]

i have been asked to replace a consumer unit and have seen that the main bonding to water and gas are only wired in 6mm. does this have to be upgraded to 10mm so that it meets current regs as its a tncs system. thanks.

 

[Octopus]

thanks len it was the esc i quoted and additions/ alterations reg in old book but the new one clears it up even better

Until you try and explain to a client that they need bonding done before you can add an outside light!

 

[Guest123]

You mention 'network circulating currents' in bonding cables. Is there generally current circulating in bonding conductors in PME systems then? I was under the impression that the only time current would flow in bonding conductors would be under fault conditions.

Courtesy of National Grid.......

[h=1]Interrupted neutral conductor[/h][h=2][/h]We explain here how the system of protective multiple earthing used in the UK produces net currents which are the main source of magnetic field in most homes. But the net current can be much bigger if pme is combined with an interrupted or broken neutral conductor.
Consider first the situation with an intact neutral conductor:

The live current has to flow in the distribution cable but some of the neutral current can divert out of the cable. This is what produces the net current. The amount of the neutral current which diverts is proportional to the impedances. Suppose the earth connection has an impedance (or resistance) 10 times bigger than the neutral current. Then 10% of the neutral current will divert and the net current is 10% of the neutral current.
Now consider what happens if the neutral conductor is broken for some reason:

None of the neutral current can return in the cable so it all has to divert into the earth (or through a link box into an adjacent circuit). The net current is now 100% of the neutral current.