Earthing puzzle


Postby prbaxter » Fri Mar 14, 2008 10:49 pm

If you use plastic piping, do you need to earth the piping at some point?

I ask, because although the pipe doesn't conduct electricity, does the water in side the pipe? Or is the water in side the pipe naturally earthed?
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Postby Kenj » Sun Mar 16, 2008 1:33 pm

It is not possible to earth plastic piping as plastic is an insulator.
You can only earth conductors of electricity - mainly metals.

Your main fuseboard should have an earth connection to the incomming water main, assuming that this is made of metal. New water pipes are blue and made of polypropolene, so cannot be earthed either.

The water in the pipework is also a conductor, so as long as there is water in the mains supply pipes, and this water flows through a metal pipe that is earthed then a theoretical earth exists. However, this may be of poor quality, and is unpredictable, as the water board can fit new poly pipe at any time.

Earthing through water would not be acceptable to the Electrical regulations.
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Postby Skids » Sun Mar 16, 2008 2:30 pm

Hi prbaxter

Equipotential bonding

The purpose of EB is to protect against indirect contact with electricity and to automatically disconnect the supply IAW the requirements of the Wiring Regulations (BS 7671:2001) and to stop the Leo Sayer look!

Metal pipework can provide a route for stray electric current to go to earth. This could cause an electric shock for someone touching the ‘live’ pipework unless the metal is properly earthed. It can also cause the pipework to corrode.

Therefore, “If you use plastic piping, do you need to earth the piping at some point?â€
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Postby smudger » Sun Mar 16, 2008 4:19 pm

Depends on whether you are connecting plastic to existing copper, back to copper; in which case you need to put a 'jumper' earth wire (4mm min) between the two copper pipes.
However if your installation is completly plastic you don't need any supplementary bonding because what are you earthing to?
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Postby prbaxter » Sun Mar 16, 2008 8:22 pm

good points guys, thanks.

So, for example, a radiator in my bathroom, where there are no electrical sockets (other than the light fitting).

If I install a chrome plated towel rail, and plumb it to the existing central heating pipes made of copper, does it require earthing? Or is it already earthed?

Alternatively, if I have the radiator connected to plastic piping, then connected to copper, does that require earthing? the rad is isolated from the copper pipe.

The same kind of goes for all the plumbing in the bathroom, basin and bath taps and shower, which will be metal, but will mainly be plumbed in with plastic piping.

btw, the main cold water pipe under the house is lead, then goes to copper as passed through the dreaded water meter.

My sparky was talking about installing an RSD (?) for the bathroom, but he said I didnt need that if I used plastic piping.
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Postby smudger » Sun Mar 16, 2008 10:13 pm

If your connecting to the existing copper heating then yes you definitly require an earth to the rad especially if you use platic pipes between as whomever touches the radiator when a fault is present (say pump live going to casing) & the earthing to your house isn't up to scratch, then that person potentially becomes the earth point for the radiator/house! Bzzzt!!

But If all pipework is plastic then as water has a resistance & the longer the run then the higher the resistance which reduces the voltage potential so negating the need for earthing any metalwork such as taps etc (impractical to do so anyway; I know I wouldn't want an earth tag & wire wraped around my franke's!! haha).

Your electrician should be able to advise you fully, he was probably talking about an RCD (residual current device) the newly released 17th edition regulations have an ever increasing requirment for these.
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