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Main bonding in a split property

Alan B

I am currently doing an EICR in a large thatched cottage that has been split on to a main house and small rental.

They share one supply but have separate DB's and are on a single TT earth,

They also have a single 30mA RCD protecting both properties, not great for selectivity but at least there is RCD protection.

Main bonding is in place to the oil feed for both properties.

The properties share a single water supply that's bonded when it enters the main property but all the pipework in the second property is giving me a reading of 0.54 ohms. My working assumption is some plastic pipe somewhere along with supplementary bonding to a lighting or power circuit. I believe the pipes just run through the fabric of the building rather than going in the ground but the outer walls of the property are damp, quite a bit of corrosion in back boxes etc, and the pipework is partially buried in the walls in places.

In my mind at least if the walls are damp they are probably also conductive to some extent and providing a path to earth,  I would love to be able to run an insulation test on the pipes but so far I cant find the supplementary bonding to disconnect it.

Ze 47 ohms, Zs at DB 22 ohms.

The MET is more or less diagonally opposite where I would need to make a bonding connection, therefore getting a bond in place is far from trivial.

Would you agree that I probably have no choice and need to find a way to get bonding in place

Is it worthwhile me spending more time trying to locate and isolate the supplementary bonding or is it very likely that an insulation test between the pipes and MET will come back below 22K because of the damp walls.

If I was to make a crimp connection to an existing 10mm earth bonding cable outside and protect it with amalgamating tape would this be acceptable or would I need to give it better protection?

Thanks

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  • 0

    By all means note in the report that a single RCD is vulnerable to total loss of power if there  is single problem appliance, and that it could be split into independent zones to lessen that problem.  I'd not fail it on that though. My point is that there are lots of situations wired like that where it is not such an issue.  I thought you were attacking the TT as dangerous and that surprised me.
    Mike

  • 0 in reply to mapj1

    Some more information

    The rental part of the cottage has not been let out for more than 5 years, customer occasionally has friends or family stay. I know this is true because I live opposite him.

    I have still strongly advised rectifying the sittuation, he worked on HV power networks in the past and fully understands the issue. He is reluctant to pay out for installing 2 new boards plus type 1 / 2 SPD as we are on overhead lines. It's a thatched cottage, plastic consumer units, no spd, no AFDD's. His insurance company say they will consider accepting C3's; my feeling is they will probably force the DB's to be changed anyway once they see the report.

    By the way I found a length of plastic pipe in the loft connecting the two properties. My plan is to run a bit of G/Y in parallel with it, which I think will restore full earth continuity on the pipework. Heating systems were replaced in both properties since the last EICR.

  • 0 in reply to Alan B

    DB change on which ground (or grounds)? If AFDDs were shown to be effective, they would certainly be an advantage in a thatched cottage.

    Alan B said:
    It's a thatched cottage, plastic consumer units, no spd, no AFDD's. His insurance company say they will consider accepting C3's; my feeling is they will probably force the DB's to be changed anyway once they see the report.
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  • 0 in reply to Alan B

    DB change on which ground (or grounds)? If AFDDs were shown to be effective, they would certainly be an advantage in a thatched cottage.

    Alan B said:
    It's a thatched cottage, plastic consumer units, no spd, no AFDD's. His insurance company say they will consider accepting C3's; my feeling is they will probably force the DB's to be changed anyway once they see the report.
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