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Topic Title: No RCD on TT system.
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Created On: 27 February 2013 07:53 PM
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 27 February 2013 07:53 PM
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daveparry1

Posts: 5888
Joined: 04 July 2007

Hi all,
Installed an outside socket for a garden water feature today, swa under some paving stones and under a bit of the lawn, usual sort of stuff. Fairly modern Crabtree c/unit in place but no rcd, so I checked the Zs at the ring socket I was going to spur from and got 0.67 ohms, used an rcd spur and done the job. It was only when having a closer look at the intake to check the earthing type to put on the MWC I realised there was no suppliers earth connection. People said the house was re-wired about ten years ago. That will teach me to look more closely before startig a job won't it, the low Zs obviously coming from the bonding and next doors earthing system!


Dave.
 27 February 2013 09:40 PM
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slittle

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Been there Dave,

I've had a couple of farms where I've gone there on recommendation to do a small job, it all measured ok in the "distant barn". When I've asked to see the intake you suddenly realise there is nothing there !


Stu
 27 February 2013 09:57 PM
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daveparry1

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Hi Stu,
I know I should have taken more trouble to check it out when I started the job but the c/unit was in a nice clean & tidy (there's a first!) understairs cupboard with a light in it, grey t/e cables coming out of the c/unit, a new looking 6 way earth block next to the cut-out with 4 or 5 earth cables going into it, iit all looked so neat and tidy and coupled with the low Zs I could have put money on it being a TN system, anyway i've suggested they call their suppliers and request PME, or if they lose the will to live whilst trying to deal with them I could change the c/unit!

Dave.
 28 February 2013 08:05 AM
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dickllewellyn

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Might pay to put an up front rcd in? At least issue some sort of non compliance or danger notice. If something were to happen, you want to make sure you are not "the electrician that came"!

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Richard (Dick)

"Insert words of wisdom and/or witty pun here"
 28 February 2013 08:39 AM
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daveparry1

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Yes Dick, thanks i'll note it on the MWC, at least my addition is rcd protected though,

Dave
 28 February 2013 04:22 PM
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dg66

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Originally posted by: daveparry1

Yes Dick, thanks i'll note it on the MWC, at least my addition is rcd protected though,



Dave


But none of it complies with the regs in respect to 132.16

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Dave(not Cockburn)
 28 February 2013 05:00 PM
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daveparry1

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By the letter of the regs. correct DG but the ring socket I spurred from has a Zs of 0.67 ohms and at the end of my extension the measured Zs was 0.78 ohms so well whithin the limits for the protective device, coupled with the fact that there's an rcd feeding the extended part of the circuit the disconnection times are well whithin limits.
I consider this is using the regs. as intended, as a guide rather than parrot-fashion, the job is safe, as is the house installation itself due to the satisfactory Zs's, (admittedly probably using a neighbours earth connection!) I think they want me to replace the c/unit anyway,

Dave.

Edited: 28 February 2013 at 05:08 PM by daveparry1
 28 February 2013 08:51 PM
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Grumpy

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anyway i've suggested they call their suppliers and request PME, or if they lose the will to live whilst trying to deal with them I could change the c/unit!

I know we all love bashing the DNO's but credit where credit's due, I have phoned SSE four times (as in four different installations) in the last six weeks asking if PME was available and in each case they responded within three days (it was available) and made no charge. Initially I went through the call center but subsequently phone Power Distribution direct. Can't fault them, they phoned me to acknowledge the request and their engineer phoned me to arrange access.
 28 February 2013 09:34 PM
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dg66

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Originally posted by: daveparry1

By the letter of the regs. correct DG but the ring socket I spurred from has a Zs of 0.67 ohms and at the end of my extension the measured Zs was 0.78 ohms so well whithin the limits for the protective device, coupled with the fact that there's an rcd feeding the extended part of the circuit the disconnection times are well whithin limits.

I consider this is using the regs. as intended, as a guide rather than parrot-fashion, the job is safe, as is the house installation itself due to the satisfactory Zs's, (admittedly probably using a neighbours earth connection!) I think they want me to replace the c/unit anyway,



Dave.


The potential problem you've got is if the shared earth disapears ( for example if the metal service pipe shared with next door next door changes to plastic) its not an earth fault on the circuit you've installed, but an earth fault on any other circuit ,as the CPC on the new socket could be at or near 230V along with the earthed chassis of anything plugged into the socket, and the RCD you've installed isnt going to trip.

I have made an assumption based on your OP that the earth path is via a shared metalic service pipe and next doors bonding.

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Dave(not Cockburn)
 28 February 2013 11:03 PM
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daveparry1

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Yes that does concern me too DG, I have asked them to contact their supplier re- pme, in fact i'll probably do that myself if they haven't done so in the next few days, although they do seem quite interested in having me change the c/unit,

Dave.
 28 February 2013 11:48 PM
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dg66

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Probably the best way to go, change CU and install new rod, proper TT.

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Dave(not Cockburn)
 01 March 2013 12:21 AM
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daveparry1

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There is a rod present with a 10mm earthing conductor going to the earth block next to the cut-out, it seems very strange, doesn't look as though it was all done many years ago really, bonding all nicely installed, looks like they done everything properly but forgot to put an rcd in! Having local knowledge and experience of the area I think there was probably an old re-wireable board there with a voelcb which has been changed by someone that didn't know an rcd was needed on a TT system!
 01 March 2013 07:21 AM
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ebee

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"someone that didn't know an rcd was needed on a TT system! "

OH Dear!

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Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 01 March 2013 08:10 AM
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alanblaby

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Originally posted by: dickllewellyn

At least issue some sort of non compliance or danger notice. If something were to happen, you want to make sure you are not "the electrician that came"!


On this subject, I'm in a similar situation, TT supply, no RCD. I've quoted to put it all right, but now all he wants is a shower CU putting in, so that he can have an electric shower.
In that situation, would a note on the EIC, noting that no other circuit has RCD protection be enough, or should I write out a 'Danger' notice?


Ta
Alan.
 01 March 2013 08:36 AM
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dickllewellyn

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Personally I opt for the danger notice and a note on the EIC. The trouble with the latter, is that if the client even reads it, it probably won't mean much to them, and they will have that golden certificate for the work done. At least with a danger notice, the clue is in the title and they just might do something about it, and certainly can't say they weren't told.

I've seen it more than once where an electricians quote to change a consumer unit was too high, so they've either got someone in for cash or bought one from screwfix and had a go, split board (16th time frame) half the circuits beautifully protected by 30mA RCD, half the circuits with only MCBs as protection.

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Richard (Dick)

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 01 March 2013 08:49 AM
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Jaymack

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Simples ........... after having explaining the pitfalls. An agreement to install a front end RCD is the only way, if the customer can't afford a proper job. The method of earthing should have been determined at the time of quoting, ASSUME can mean?

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