Outside tap

[marcuswareham]

Hi all

I am on a TN-C-S / PME supply and have an outside tap, I have fitted it with 5 speedfit plastic elbows and a speedfit all plastic valve. So having so much plastic in place that should be the recommended insulated section of pipe to prevent dangerous voltages being on the tap in the event of a PEN failure

With the pipes full of water the resistance between the MET and the outside tap is 1726 ohms, so I work that out to be a potential current of 133mA which is still enough to be potentially fatal?

Please correct me if I am wrong here?

I know people say the risk of a PEN fault is so low you don't worry about it, but if it never happened why all the regulations for EV charging from PME, also I live in a very windy little village with individual overhead cables from the transformer down the street and UK power networks are often out to repair them. Information from UK power networks would indicate there is an electrode at the transformer and 2 more down the road, it seems the nearest to my house is 8 poles away and some of those poles look as if they could fall down lol, so if its gonna to happen anywhere I guess it would be here.

Thanks Marcus

 

[davesparks]

If the poles come down then you'll far more likely loose all conductors, not just the PEN.

Is it ABC or seperate cables on the poles?

What do you mean by a recommended insulated section of pipe? I'm not aware of any recommendations regarding this.

 

[radiohead]

I think you are worrying unnecessarily. However a simple step you could take is to install an earth electrode to the earthing system which would reduce or eliminate the miniscule risk. This was in fact considered, and rejected as a requirement of the recent 18th edition of the regulations.

 

[davesparks]

As I've mentioned on your other threads, a couple of earth electrodes connected to the MET of the installation will help reduce the risk.

 

[radiohead]

What do you mean by a recommended insulated section of pipe? I'm not aware of any recommendations regarding this.

I suspect this is a confusion regarding main bonding, where it has been clarified in the 18th that an insulating section at the point of entry negates the requirement for main bonding, however that is not the same as recommending an insulating section should be present.

 

[marcuswareham]

If the poles come down then you'll far more likely loose all conductors, not just the PEN.

Is it ABC or seperate cables on the poles?

What do you mean by a recommended insulated section of pipe? I'm not aware of any recommendations regarding this.

Hey no its is not aerial bundled cable it is separate cables and from what I can tell to an untrained eye the PEN is the bottom one, so that was what I meant about the likely hood of just one cable i.e the PEN breaking. Yes exactly see what you mean that they would most likely all go if a pole falls down, but maybe something less dramatic might kill the PEN

Sorry the insulated section of pipe recommendation is an un-official recommendation I have read on a few forum posts etc, so what people say they do etc
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As I've mentioned on your other threads, a couple of earth electrodes connected to the MET of the installation will help reduce the risk.

Exactly doing the math to get under touch voltage the earth electrodes would have to be around 1-3 ohm mark, I am fairly sure I will not achieve that
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[telectrix]

why not fit a plastic tap?

 

[davesparks]

Sorry the insulated section of pipe recommendation is an un-official recommendation I have read on a few forum posts etc, so what people say they do etc

Exactly doing the math to get under touch voltage the earth electrodes would have to be around 1-3 ohm mark, I am fairly sure I will not achieve that
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I've never seen that recommended on this forum.
Obviously it's dependant largely on exactly what is in the water at any one time, so hard to calculate exactly, but I think for 15mm pipe the plastic section needs to be well over half a metre to have any chance of achieving a high enough resistance with the 'average' hard water in the UK.

 

[marcuswareham]

Does anyone know of any other way to mitigate against it, our outside tap is in regular use and it is above soil and a few loose stones and of course the floor gets wet increasing conductivity

I did try a plastic tap, but they are hard to get hold of (or at least good ones) the one I got hold of was a bit pants, it was on for about 4 days then the treads broke and it shot its self across the drive.

Also how would you work out the touch voltage on the tap should you have a PEN fault, I know the impedance of my extraneous conductive parts without them being connected to the MET, however what would you put in for the current as who knows how many houses would be on the same conductor
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why not fit a plastic tap?

Sorry I think I was typing at the same time, I tried plastic tap, didnt end that well

 

[davesparks]

I suspect this is a confusion regarding main bonding, where it has been clarified in the 18th that an insulating section at the point of entry negates the requirement for main bonding, however that is not the same as recommending an insulating section should be present.

Which is still something I don't like, they really should have specified how long the insulating section should be, or at least that testing must still be carried out.
As has been proved in this thread a short section of plastic water pipe isn't enough as the water itself has some conductivity