MET and bonding questions.

[imago]

The CU change I'm doing at home for my ELECSA assessment will obviously include upgrading of the MET and returns from the board to it. Am I right in thinking that the earth from there to the incoming cable (before the head) is the responsibility of the DNO? I will measure the Zs as well as crunch the numbers and calculate it, but even so the bare twisted wire really should be changed IMHO. So I guess I'd need to contact EoN (Birmingham) and get them to upgrade it? See pic attached if you need a visual.

The bonding question concerns the water pipe. There are two earth cables running under the floor which are presumably for the water and gas pipes. Both need upgrading, and the gas is straight forward just a pain to pull the cable to. The water is a bit of an odd-ball in that the water pipe where it enters the kitchen (extension) is plastic. I suspect (will confirm when I lift the boards) that the lead pipe runs so far in, then Bob-the-builder has extended it with plastic. So the lead section may well still be bonded under the old floor. That means that the copper water pipes in the house will be separated from the water earth connection, but may be picking up a path through the boiler or other touching metal concealed from view.

So, options:-

1) I can upgrade the earth to the lead pipe, then link that to the copper immediately after the plastic at the stop tap.
2) I can ignore the lead and earth the copper (cold, hot, and CH cross bonded) where they pass reasonably close to the CU to provide a better path than through the boiler or random metalwork.
3) I can link the pipework as in 2) then link that to the lead which is close to it and the CU.
4) Something else?
5) Become a plumber instead.

 

[Engineer54]

If your conserned about the CSA of the DNO's sweated earthing conductor, then upgrade to a suitable CSA using constant tension spring clamps and flexible mesh conductor. The chances are, that the DNO will want to charge you for any upgrading. DO NOT use the typical pipe type earthing clamps!!!

As the water lead/cooper pipe, after the plastic pipes will probably be connected via the boiler anyway, it's up to you, if you want to bond the copper side of your installation, it'll certainly be less than the 23,000 ohm required.

 

[GLENNSPARK]

we had this scenario a while back at a job in barnsley....main earthing was an old un insulated twisted wire clamped on with a BS951.....about 4mm csa i think on a TNS.....needless to say the Ze was high.....

 

[Knobhead]

Constant force springs

Constant Force Springs : 3M UK & Ireland

 

[imago]

Thanks for the info gents. I'll put the meter on it and see what we have then go from there I think.

As the water lead/cooper pipe, after the plastic pipes will probably be connected via the boiler anyway, it's up to you, if you want to bond the copper side of your installation, it'll certainly be less than the 23,000 ohm required.

I agree it's probably OK as it is currently. But as everything is earthing through the boiler and gas pipe it only takes a remade joint (PTFE tape) or a change of copper to plastic pipe somewhere and there'll be no continuity. I can't see too many plumbers checking the earthing when/if they work on it. So I figured whilst I was working on it anyway it'd be a good time to add a belt to go with the braces.