Detail of main / equipotential bonding.

[Trog]

I am part way through wiring a new extension on my house, as part of this I have replaced the CU for a more modern one with RCD protection. From reading replys to earlier posts I know I have to upgrade the main earth bonding, and the equipotential bonding for the bath & shower rooms, before the LABC electrician comes round to check it all over and test. As I believe the existing main bonding is too light (6mm), and I am not sure that the equipotential bonding is all it could be.

I just wanted to double check the detail of what is required for the bonding before I start drilling holes etc.

On the main bonding I know I have to bond together the meter earth block, gas and water pipes where they enter the house, and the consumer unit with 10mm earth cable. (No other metal pipes etc to house)

I know from earlier posts that I can use the same cable to bond the water and gas provided I do it with one continuous cable. My question is can I have a joint in the earthing at the CU. ie cable from meter earth block to CU, then a second cable from CU to pipes, or two cables from meter block one to CU and one to pipes?

On the bathroom front I have two adjacent rooms sharing the same water supply pipes etc is it OK to treat this as one equipotential zone?

In these two rooms I have two showers one electrically heated with its own 10mm cable back to the CU, and the other pumped off the central heating drawing power off the ring main via a 3A fused connection unit.

I believe I have to bond the lighting circuit earth, the earths to both showers, radiator feeds and the H&C water pipes together in 6mm earth cable. Do I have to achive this with one length of cable, or am I allowed to join the cables together at a central point, or even have two seperate sections of cable using one of the copper pipes to provide the connection between them?

The old main bonding is buried in the wall and unrecoverable, if I have enough spare terminals would it be OK to leave it connected as a back up to the new? As I don't like leaving orphan cables behind me as I feel they are a potential cause of confusion / trouble in the future.

 

[comms]

can I have a joint in the earthing at the CU. ie cable from meter earth block to CU, then a second cable from CU to pipes, or two cables from meter block one to CU and one to pipes?

You can do either but make sure you put a "safety electrical connection do not remove" label on or near the MET if it's remote from the cu. I use one from a BS951 clamp.

is it OK to treat this as one equipotential zone?

Cant see why not, so long as the pipework isn't unbroken by plastic fittings/pipe.

believe I have to bond the lighting circuit earth, the earths to both showers, radiator feeds and the H&C water pipes together in 6mm earth cable

4mm will suffice (2.5mm if protected).
Bond from light earth to shower earths then to pipework.

am I allowed to join the cables together at a central point,

Again cant see why not.

or even have two seperate sections of cable using one of the copper pipes to provide the connection between them?

This can be done.

if I have enough spare terminals would it be OK to leave it connected as a back up to the new?

If you want to but you could just as easily cut it off, but hey its your job

 

[Trog]

comms thanks for the help, it is very reassuring to have my understanding checked before I commit it to copper.

With the LABC check up still to come I feel like I am sitting an exam.

 

[comms]

comms thanks for the help, it is very reassuring to have my understanding checked before I commit it to copper.

Not a problem glad to help. Better to ask than stumble on blindly

With the LABC check up still to come I feel like I am sitting an exam

Dont worry about it, be nice to the chap/chapess & all will be ok, remember they probably know next to nothing about sparking if its the BCO doing the checks.