TT System Query

[sbrown2]

Good Morning

I would like some advice.

Working on a Domestic TT System. Primarily a kitchen refurb. The customer in my case is the contractor. I told him there should be an earth electrode around. I tried to locate and could only locate 6mm earth cable to a disused lead water pipe. Eventually found the earth electrode with the cable disconnected. The original consumer unit has no RCD protection and is around/at least 25 years old. I've been told to ignore this consumer unit and fit new for the kitchen with 30mA protection.
Questions

1. If resistance readings are ok can the lead pipe suffice as the earth electrode?
2. Would you put the disconnected electrode back into service if the tests are good?
3. Is it normal practice to leave customer CU and fit new one to specification?

Any help would be appreciated.

 

[Guest 004]

ans 1. NO
2. YES
3. up to you

Try and get an earth reading between Phase and Neutral, for your Ze ( two lead tester required ), if you get reading below 0.35 ohms. Then ring up the Local leccy board, and ask for a PME supply. Or you could just link the neutral to earth yourself

 

[Deleted member 9648]

Good Morning

I would like some advice.

Working on a Domestic TT System. Primarily a kitchen refurb. The customer in my case is the contractor. I told him there should be an earth electrode around. I tried to locate and could only locate 6mm earth cable to a disused lead water pipe. Eventually found the earth electrode with the cable disconnected. The original consumer unit has no RCD protection and is around/at least 25 years old. I've been told to ignore this consumer unit and fit new for the kitchen with 30mA protection.
Questions

1. If resistance readings are ok can the lead pipe suffice as the earth electrode?No...542.2.1.......542.2.4
2. Would you put the disconnected electrode back into service if the tests are good?Your call,depends on location and condition,I'm not on site.
3. Is it normal practice to leave customer CU and fit new one to specification?

Any help would be appreciated.If it is going to be a TT You would be leaving the existing install with no RCD protection and hence inadequate earth fault protection,even if you havent worked on the existing it would not be acceptable IMO/COLOR]

........

 

[Dunc]

Think most of it's been said already so far so just to add a couple of points. By all means reuse the old electrode, remember you're looking for a reading <200 ohms but be wary if it's only a little under this when the ground is wet as the reading will soon go way up come the summer and could potentially cause the RCD to not operate properly. Also make sure the electrode is suitably covered and labelled to provide protection against corrosion, impact and removal. Regarding the existing stuff, if you are adding a CU you'll likely be fitting some Henley blocks, you could then fit a 100mA S type RCD before these blocks to protect the existing stuff then just a small CU with 30mA protection for the new stuff. So long as the bonding is up to scratch just put a comment in the 'comments on existing installation' box about the non conformities present. You'll atleast cover yourself then and make the installation that bit safer. Alternatively get the electricity board to fit you a PME. It'll likely put the customer back £150 but there'll be savings from not having to fit additional RCDs but you will have to ensure the bonding is replaced if under 10mm.

 

[nickblake]

DNO may not install a PME system as it could cost to much TT systems are normally installed in remote area's or may just not available ive just had a quote back for installing PME and it was over £10k will not be worth it ,

 

[Guest 004]

Like I said if the reading between phase and neutral is less than 0.35 ohms, then the cost will be minimal

 

[IQ Electrical]

The cost involved in PME relates to the installation of the protective MULTIPLE earthing points on the PEN conductor, a neutral fault loop impedance test would not give you any idea as to whether PME was available.

 

[Guest 004]

They will just link out the neutral to earth at the head

 

[sbrown2]

Thanks for the reply. I am just going back with testers now and paperwork. have been told by contractor the customer will not pay to get the electric board in.

 

[Engineer54]

Good Morning

I would like some advice.

Working on a Domestic TT System. Primarily a kitchen refurb. The customer in my case is the contractor. I told him there should be an earth electrode around. I tried to locate and could only locate 6mm earth cable to a disused lead water pipe. Eventually found the earth electrode with the cable disconnected. The original consumer unit has no RCD protection and is around/at least 25 years old. I've been told to ignore this consumer unit and fit new for the kitchen with 30mA protection.

Questions

1. If resistance readings are ok can the lead pipe suffice as the earth electrode?
2. Would you put the disconnected electrode back into service if the tests are good?
3. Is it normal practice to leave customer CU and fit new one to specification?

Any help would be appreciated.

1. Absolutely NOT!!
2. Yes, ...That's a no brainer!!!
3 NO, it's not normal practice, i would also go as far as saying, remote separate CU's in a standard sized house is a nonsense!!!

Try and convince this ''Bob the builder'' that he NEEDS to upgrade his electrical installation for his families safeties sake!!
Putting a 100mA S type RCD at the origin of supplying two CU's will do little if anything for the existing CU...
First off contact the DNO and find out if the network supply to this house has been PME'd, if it is then it will cost little to nothing for them to convert the head cut out.

If it's not been PME'd, then convince this guy that the main house CU needs upgrading with either RCBOs or RCDs as a matter of urgency as far as having a TT system without there additional protection!!! In fact if he can spend out on a new kitchen, he can spend a few more bob on making his whole house electrically safe and not just the kitchen...
Nothing stopping you driving another rod in the ground too, and linking up with the existing one. What ever you do, that existing rod needs a protective ground pit, to protect the connection in the future...

Even if you do manage to get a PME supply off the DNO, you can still take the rod earthing cable to the MET, in fact many countries insist that a local rod is installed at there TNC-S supplies MET....

 

[Deleted member 9648]

I dont think the OP is talking about a remote CU..(as you are aware Engineer your reasoning on remote CU's is beyond me but lets not go there).....just a separate one at the intake for the new circuits,which is common practice to avoid getting involved with the existing,although in this case clearly the existing does need getting involved with.

 

[Engineer54]

OK, if that's the case... I wouldn't normally see any problems with adding an additional CU, if for argument's sake the existing CU was full with no spare MCB capacity. But as you say in this case, the existing CU needs to be sorted out, and if renewing this CU, it could then incorporate enough ways to cater for the new kitchen installation...

Remote separate CUs are pretty much a nonsense in normal sized properties, there a lazy mans way of completing an installation. As you know, I have a TT system here, and i have 3, 3 phase CU's in my house that i didn't want. One i have no problems with, (controls all exterior power and lighting requirements) but the inclusion of a CU on the upstairs landing to distribute power and lighting to the upstairs rooms i do have a problem with!! lol!!

 

[sbrown2]

Thanks for the replies. I've finally spoken to the customer.

The original scenario is

1 Earth rod cable disconnected
2 Original consumer unit utilising fuse wire no spare ways
3 original Consumer Unit no RCD
4 Sockets not in kitchen impedance 2.8 ohms
5 main earth to original consumer unit 6mm to disused lead pipe.

Current Scenario not yet completed

1 RCD protected CU fitted for kitchen to include cooker, lighting and ring main with 16mm tails
2.16mm earth from disused lead pipe to earth terminal
3. Supplementary Bonding to Terminal
4.Earth Rod connected and back to earth terminal
5 Customer now aware of poor condition of his original consumer unit. Ive explained he could have saved money by upgrading to the correct CU.
6 Testing this wednesday and quoting for bringing installation upto standard

And now off to a seized motor gearbox foer the night could be atwo day job!!! So may not get back to the PC!!! So may not get back to the PC.

Anyway Adios

 

[dwe]

Dear MrEnigma, Re: your advice on creating your own PME, I really hope you have not done this your self on jobs you have attended!
A PME system needs the neutral to be earthed at several points on its route back to the supply transformer! If you have connected earth to neutral at cutout and the supply neutral is broken and phase connection left in tact, then you have a possible scenario of live earthed parts in the installation! regards dwe

 

[Guest 004]

Indeed of course I have not, hence the smiley face. Just trying to highlight the fact that if you get a reading of less than 0.35 ohms P-N, then that would mean the neutral has been earthed at the relevant points.

Was also speaking to an engineer from EDF, who also said that TT supplies have not been installed for 20 years in the UK. All NEW supplies are now PME