Incoming meter wiring under-rated?

[JohnW2]

From the 'safe' point of view I am not sure I understand why a 50Ω Earth would not be sufficient. In the event of a short between live and earth the RCD would trip, in the event of a person being the earth the RCD would also trip?

As you say, a 50Ω earth is not, in itelf, a problem - that's lower than many an earth rod in a TT installation provides. However, as I said, there is theoretically no guarantee that it will always be there - the water supply company could, one day, replace the water supply pipe virtually all the way up to your property with plastic - in which case you'd end up with little or no earth.

OK, so you are aware of this, so if you saw people with massive coils of plastic pipe digging holes outside of your house, warning bells would probably ring in your head. However, what if the house comes into different ownership?

I don't think that any electrician would, could or should do any work on your electrical installation if there was no 'proper' earth, compliant with current regulations - but I imagine that others will comment on that.

Kind Regards, John

 

[RossR]

This installation doesn't comply with 17th edition wiring regs.

BS7671:2008 542.2.4 The metallic pipe of a water utility supply shall not be used as an earth electrode. Other metallic water supply pipework shall not be used as an earth electrode unless precautions are taken against its removal and it has been considered for such a use.

If the DNO don't supply an earth, you will need a rod or similar.

 

[Kaymo]

I think thats a fair point, having an engineering background I understand the concepts here and as long as I live there there shouldnt be a problem but if I sell the house on to someone without any technical knowledge they could end up losing an earth and not knowing.

So, if I was to get an earth rod installed I presume we are talking about connecting reasonably sized, cable from the consumer unit to an earth rod somewhere on the property. Does the earth rod have to be away from the house or could it be underneath (suspended floor construction)? The reason I ask is that the CU is upstairs in the middle of a large house so the cable will need to go up into the loft then 10+ metres towards the gable end of the house to go down to the under floor area. In some way this would seem perfect as it is protected from any digging by virtue of the fact that its inside of the walls, no-one goes there except for maintenance? - I have a feeling someone is going to tell me why this is not a good idea

 

[JohnW2]

I think thats a fair point, having an engineering background I understand the concepts here and as long as I live there there shouldnt be a problem but if I sell the house on to someone without any technical knowledge they could end up losing an earth and not knowing.

Indeed, that was my point.

So, if I was to get an earth rod installed I presume we are talking about connecting reasonably sized, cable from the consumer unit to an earth rod somewhere on the property. Does the earth rod have to be away from the house or could it be underneath (suspended floor construction)? The reason I ask is that the CU is upstairs in the middle of a large house so the cable will need to go up into the loft then 10+ metres towards the gable end of the house to go down to the under floor area. In some way this would seem perfect as it is protected from any digging by virtue of the fact that its inside of the walls, no-one goes there except for maintenance? - I have a feeling someone is going to tell me why this is not a good idea

I'm not sure that it is directly addressed in the regs (except by the requirement for an adequate connection to earth), but I would have thought that under the floor is potentially too dry, and therefore could provide a high resistance earth, at least at some times of year; I certainly have never heard of that being done. The earth rod and connection thereto would also have to be accessible for inspection.

If you used 16mm² cable (0.0028 Ω /metre), a long cable run would not be a problem - the cable impedance would be negligible compared with that of the earth connection istelf. However, is there no way that you could take the cable downwards through the house, rather than via the roof?

Kind Regards, John

 

[Kaymo]

RossR,
Half the houses in the country probably dont comply with 17th ed, as its relatively new, and most of the houses were built before they were released so are the regs not intended for new installations or when major work is being carried out on existing installations?

My house was built shortly after the 1st ed.

Your quote below is interesting though as it does seem to suggest that water pipe can be used as long as "precautions are taken against its removal and it has been considered for such a use"

 

[Kaymo]

However, is there no way that you could take the cable downwards through the house, rather than via the roof?

I dont think so, everything including water and power seems to go down through a channel on the gable end of the house, power comes in from a suspended cable at loft level. When the central heating was installed many moons ago the main pipes have been run up the inside wall on the other side of the house so I think thats a sign that there was no other way to route it.

 

[RossR]

There is no requirement for existing installations to be brought up to current regs. However, if you have any alteration or extension work done on the installation then the earthing will have to be checked to see that it is adequate. At the moment I'd say it's is far from adequate.

I appreciate the installation is rather old, but I doubt it has been untouched in that time

The exemption for "precautions are taken against its removal and it has been considered for such a use" doesn't apply to public utility supply pipes.

 

[JohnW2]

However, is there no way that you could take the cable downwards through the house, rather than via the roof?

I dont think so, everything including water and power seems to go down through a channel on the gable end of the house, power comes in from a suspended cable at loft level. When the central heating was installed many moons ago the main pipes have been run up the inside wall on the other side of the house so I think thats a sign that there was no other way to route it.

It obviously depends upon how much (potentially disruptive) work you would be prepared to contemplate. Can you not route a cable under the floor (of the storey of the house which has the CU) to the nearest outside wall, and thence through a hole in the wall into the 'outside world' - or, if getting under floors is a problem, even along skirting boards (with trunking, or even just painting, if desired for aesthics)? However, living in a house of which many of the outside walls are 18 inches thick, I realise that may not be 'simple', but few things are impossible.

Kind Regards, John.

 

[westie101]

OK this is very old and an early version of PME that was used, it can't be used now but the method gives me an idea!

We used to have (still use) a system called PNB (Protective Neutral Bonding)
this was used on a lot of 1960's overhead supplies.
In this a 2 wire supply was used but at the meter position the neutral was connected to an external earth rod, with the earth wire following the incoming supply and then clipped down the outside wall to the earth rod.
(That's your history lesson for tonight)

Why not run a suitable (16mm) double insulated cable back along the route of the house service (if you ask nicely perhaps those nice SP men who install your new service might help) then clip it down the outside wall to the earth rod.
Now this might be on the edge of compliance, at the meter end use some green/yellow heatshrink to mark the cable (face it a green/yellow cable running down a house wall will look crap)
For the earth rod I would suggest at least a double length (we use 4x1.2m rods coupled together)

 

[Kaymo]

Thanks guys.

I think the first priority is probably the RCD CU, which is probably a good idea aside from any of this and this at least makes the installation safe for now.

Regarding the earth rod I will have to have a think about the best thing to do but I think the obvious route has to be up and through the loft as the CU is up high in the cupboard and nearly in the loft anyway. If I can get it to go down the same route that the water pipes come up I could take it outside through one of the vents on the side of the house and from there its on to the gravel driveway. I could probably clear an area and drive down in to there.

 

[RF Lighting]

What colour is your house painted, or what material is it constructed from?

Is there a side of the house which can't really be seen that easily?

 

[baldelectrician]

The saga continues...

Guy from SP came out yesterday, he didnt even need to check the impedance as the first thing he did was follow the line back to the pole and the earth wire is not connected at the pole, just tied back. He said that SP had never supplied an earth and so were not obliged to rectify this. If I wanted to request an earth from them it would likely be very expensive and probably would be cheaper for me to resolve things at my end.

The guy from SP came out, looked at the supply at the meter and noticed that SP have supplied an earth terminal (the earth terminal in the photo is the same as the N supplied by them)

SP will do whatever it takes to wriggle out of spending any money. If they can they will try and pass any costs over to the customer

I would take it further- ask them for this in writing, bearing in mind they have supplied an earth terminal and have disabled the earth function by their lack of action (connecting the wire)

 

[Kaymo]

What colour is your house painted, or what material is it constructed from?

Is there a side of the house which can't really be seen that easily?

Its Sandstone blocks, it wouldnt be the end of the world if we had to bring a cable down the outside of the end where the supply cable comes in but there would be no sense in doing this if it can be brought down the inside of the brick at the other end where the water pipes come up.

 

[Kaymo]

The saga continues...

Guy from SP came out yesterday, he didnt even need to check the impedance as the first thing he did was follow the line back to the pole and the earth wire is not connected at the pole, just tied back. He said that SP had never supplied an earth and so were not obliged to rectify this. If I wanted to request an earth from them it would likely be very expensive and probably would be cheaper for me to resolve things at my end.

The guy from SP came out, looked at the supply at the meter and noticed that SP have supplied an earth terminal (the earth terminal in the photo is the same as the N supplied by them)

SP will do whatever it takes to wriggle out of spending any money. If they can they will try and pass any costs over to the customer

I would take it further- ask them for this in writing, bearing in mind they have supplied an earth terminal and have disabled the earth function by their lack of action (connecting the wire)

I did question this, I made the comment that the earth was not only tied in to the outside of the house but also run all the way back to the pole giving the impression that they were supplying an earth but he said that this was probably just done so that it could be tied in if an earth was installed. There doesnt seem to be any legislation that covers this that I am aware of so it would appear if they say they are not supplying an earth then that would seem to be the end of it. You would think that given the amount of time spent producing endless domestic regs that a sensible regulation would be to make the power companies responsible for all earths.

I am going to ask my neighbour where his earth is coming from as his is a fairly modern construction, built on what used to be part of the garden of this house so he must be using the same supply. If he has an SP supplied earth then obviously there is one there and SP just dont have mine tied in, but if he has his own earth then I am probably on a hiding to nothing.

 

[westie101]

Get the camera out and take a photo of the pole top and the ones either side!

(in daylight tomorrow of course)