Water co. upgrading supply pipe to plastic. Earthing issue?


Postby matt20uk » Fri Jul 23, 2010 12:20 pm

Hi all,

Bristol Water will shortly be upgrading the main water supply pipe in my street to a plastic pipe. They have warned that some houses built before 1966 (mine is 1930s) may use the current metal water supply pipe for electrical earthing and I should get an electrician to check if my property will be affected.

Clearly, I need to get an electrician to check this out. How would an electrician go about testing my earthing arrangements? How much should this cost?

One thing to note is that the water pipe from my property to the main is lead (I think). Does this make it more likely that I have alternative earthing arrangements?

Thanks in advance.
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Postby sparx » Fri Jul 23, 2010 3:01 pm

no, as pipe should not be your main earth, only bonding for pipework your side of stopcock
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Postby ericmark » Fri Jul 23, 2010 7:43 pm

If the occupiers have followed IET/BSI recommendations and had the installation checked on change of occupier or every 10 years which ever is shorter any problems should have been picked up.

However solicitors have missed having checks referred to as Periodic inspection reports (PIR) many times and it is not uncommon to find faults like no earths on lights which was outlawed in 1966 still evident on properties today.

The incoming gas and water mains are bonded but this should be connecting the water pipes to main earth not using water pipes as an earth.

There are three earthing systems

TN-S with this the electrical supply authority supply the house with an earth which goes all the way back to sub-station.

TN-C-S with this similar to above but one cable is used both for neutral and earth. As far as house holder is concerned the only difference is the Earth Loop Impedance (ELI) which with TN-C-S is 0.35 ohms or better and with TN-S is 0.80 ohms or better.

TT This uses an earth rod and as a result will always have an "Earth leakage circuit breaker" (ELCB) these were originally voltage types (ELCB-v) but were latter replaced with current types (ELCB-c) and have a load of different names. RCD, RCCB, GFCI, GFI, ALCI and also combined with current overload RCBO. They all have a test button to test the mechanical operation.

The supply authority are duty bound on enquiry to tell you what system you have. Although it often takes some persistence to get them to tell you as often they need to send someone out to test and of course that costs them money.

In theory you only need to check the paperwork from last PIR. In practice PIR's are often missed. If so for your own safety you should get one done. However if either of the TN systems are used you will normally see an earth cable coming from the supply head into your fuse-box/consumer unit. And if TT system you should be able to find earth rod.

However with the latter earth rods were also used with party line telephone lines so do ensure the earth rod is connected using a green or green/yellow insulated cable. Party lines were normally non insulated cable.

On other forums we would ask for photos showing the supply head but this forum does not allow photos. Maybe using a forum where photos are permitted would be a good idea.

Up to 2008 when the regulations changed we would do all we could to get the supply authority to give us an earth. They don't have to provide one but in town they normally will. All properties from same transformer have to have same type of earth and Petrol Stations are not allowed to have TN-C-S so some times TT is still used.

The BS7671:2008 required all sockets under 20A and cables buried in a wall at less than 50mm unless special cables to be RCD protected. This in real terms means everything now has to be RCD protected with a TT system this needs to be double pole but with a TN-C-S single pole switching is permitted but what is loosely referred to as a 17th Edition consumer unit has two RCD's and it would not really matter is TT or TN system any more since everything is RCD protected. With the TN-C-S system the single pole switching RCBO can be used one for each circuit which reduces unwanted tripping but they also cost more.

To call the supply authority to ask what is your supply type would mean if it is TT the opportunity to persuade the engineer who calls to give you a free up-grade to TN instead would be likely lost. As electricians we can often persuade the engineer to give us a TN system. Once they have called and ID'ed the type then if it is TT you will likely be charged to up-grade.

For what it will cost to get an electrician to call and test your earth I would consider that as money well spent. We use a meter called an "Earth Loop Impedance" meter which are expensive but tell us the value of the earth system. There are other ways but all include expensive meters and some knowledge to test correctly and safely so I would recommend you get an electrician to call. If you can afford it I would also recommend a full PIR.

And full marks to your water authority for warning you. They do not have to tell you it is really up to you so they are being very good warning you. They didn't with my parents house and when I came to do some work I found they had no earths at all.
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Postby matt20uk » Thu Jul 29, 2010 1:05 pm

Ericmark, thanks for your very comprehensive reply.

I have contacted Western Power, who I believe is responsible for electricity supplies in the Bristol area. They said that they do not know what type of earthing arrangement I have and I will need to get an electrician out to confirm this.

Are you able to provide any assistance in getting Western Power to tell me what system I have?
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Postby ericmark » Thu Jul 29, 2010 5:35 pm

When we as electricians are taught we are told we can find out items like earth loop impedance at the head by inquiry to the Electricity Distribution Network Operators (DNO) in the main we can see as electricians what the supply is but sometimes it's not plain and since all supplies from the same step down transformer should be of same type the only people who can answer the question as to supply type is the DNO.

From:-
Statutory Instrument 2002 No. 2665
The Electricity Safety, Quality and Continuity Regulations 2002

It states:-

Information to be provided on request
28. A distributor shall provide, in respect of any existing or proposed consumer's installation which is connected or is to be connected to his network, to any person who can show a reasonable cause for requiring the information, a written statement of -

(a) the maximum prospective short circuit current at the supply terminals;
(b) for low voltage connections, the maximum earth loop impedance of the earth fault path outside the installation;
(c) the type and rating of the distributor's protective device or devices nearest to the supply terminals;
(d) the type of earthing system applicable to the connection; and
(e) the information specified in regulation 27(1),

which apply, or will apply, to that installation.

Under (d) above it is clearly the responsibility of the DNO to tell you what earthing system you should have.

However you can't use this power to get a free TN-C-S connection once they have visited and up-dated their records, and it is common for us electricians to demand to be told what the earthing arrangement is in order to force a visit and persuade their man to give us a TN-C-S earth. It may pay you to get an electrician to look at your supply first. If you have a TT supply that means earth rods are required.
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Postby jimmy_one_ball » Tue Aug 03, 2010 10:04 pm

Plastic water pipes will not introduce a zero potential, namely they are non conductive, so they will not need to be bonded.

I think this is probably the main concern.

As regards the earthing system your local distributor is legaly obliged to confirm the type of earthing arrangement that you have free of charge. Don't take no for an answer, quote regulation 28 of the Electrical Safety, Quality and ContinuityRegulations 2002 (ESQCR2002) and watch them jump! They simply MUST tell you or they are breaking the law.

It will almost certainly be a TN-S system which means there is no way your water pipes will be used as an earthing electrode in which case don't worry.

Would be interested to learn of their response!

All the best
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Postby matt20uk » Tue Aug 10, 2010 12:16 pm

Hi all

In the end, I decided to get a periodic inspection done.

It was a good job that I did. The electrician advised that although I have a TN-C-S system, the earth cable from the main breaker to the consumer unit was not connected! He connected it up for me free of charge.

Aside from that, the inspection gave me some peace of mind as to the electrics in the house. There are a couple of minor points to be resolved, which are:

- swapping one of the circuit breakers for one with a lower rating

- earth bonding the main gas supply (hence my new post (http://www.diydoctor.org.uk/forums/view ... highlight=)
matt20uk
Posts: 8
Joined: Fri Jul 23, 2010 12:16 pm


Postby matt20uk » Tue Aug 10, 2010 12:18 pm

Hi all

In the end, I decided to get a periodic inspection done.

It was a good job that I did. The electrician advised that although I have a TN-C-S system, the earth cable from the main breaker to the consumer unit was not connected! He connected it up for me free of charge.

Aside from that, the inspection gave me some peace of mind as to the electrics in the house. There are a couple of minor points to be resolved, which are:

- swapping one of the circuit breakers for one with a lower rating

- earth bonding the main gas supply (hence my new post (http://www.diydoctor.org.uk/forums/view ... highlight=)
matt20uk
Posts: 8
Joined: Fri Jul 23, 2010 12:16 pm


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