Dual fuel towel rail bonding

[RegPrescott]

Just a quick one to set my mind at ease about suplimmentary bonding where there are plastic pipes ( I saw the thread that battled through November).

I've got a dual fuel heated towel rail to be fitted in the bathroom and the pipework to supply it is plastic.

I've read the document on the IEE site regarding earthing plastic pipes Here. It looks to me like the rail won't need supplimentary bonding. For one the rail won't need bonding because of the plastic supply and secondly it will essentially be supplimentary bonded already from where the element is wired to the earth in the FCU outside of the bathroom.

Do you think that this installation would need an extra earth?

 

[securespark]

I wouldn't, because as you say, it is fed by plastic pipes, but the regs do say supplementary bonding should be installed not only from extraneous conductive parts ie pipe to bath to radiator etcetera, but also to the cpc (earth wire) of each appliance within the bathroom, like shaver point, lighting, shower, fan immersion heater etcetera.....

 

[RegPrescott]

Thanks for your help with that.

It's good round here isn't it!

 

[another_sparky]

Anyone have any views on this piont:

If a plastic pipe is connected to a copper pipe, and, the copper pipe somehow gets a live cable touching it...
doesn't that send the water inside the pipe 'live'. Thus the power would be carried within the plastic pipe to the metal radiator?

 

[securespark]

Another spark

Have had this kind of discussion with IEE in the past.

They say they have run tests (didn't ask what) and discovered there is no hazard from what you describe.

If a metallic object is isolated by being connected to plastic piping, then there is no need to bond.

But you still have to bond every other extraneous conductive part and the cpc's (earth wires) of electrical circuits feeding equipment in the bathroom.

 

[il78]

Bit of a story.....

When I was at college doing the 2391, plastic pipes onto copper came up for discussion (well argument really). The lecturer told us that an earth bond would not be required because the voltage / current could not pass through the plastic pipework nor the water within......not one for backing down , a little experiment was set up involving a bowl of tap water and an IR tester.....one probe in the water the other probe in his hand, the lecturer was not that confident in backing his words of wisdom now, he did not play ball, but another spark did.....he did get meggered, but it wasn't as bad....now would the same thing happen in a domestic situation, I honestly don't know......any-one want to try..?

I think the IEE need to adopt a decent testing method

 

[AdamW]

If it were plain old mains water, I would agree that the water isn't conductive enough to pose much of a risk. However as this is central heating water it is chock full of chemicals that could make the water conductive enough to cause problems.

Now, what causes a problem with this would be a 2-point failure (i.e. something making pipe live at one point + no bonding at towel rail). I would say better safe than sorry. "Over earthing" doesn't cause problems in the domestic environment. Physics laboratories however...

 

[another_sparky]

thanks guys.

I always bond rads and exposed metalwork in the bathroom regardless of plastic piping.( It may take longer and be unnecessary in the eyes of the IEE - but I prefer to do it.

 

[securespark]

The IEE would argue otherwise about "over-bonding".

They have decided to scrap bonding in a kitchen (at sink & taps) because after their testing, have decided that the installation could be less safe bonded than not.

Ian - Why don't the IEE have a "decent testing method"?

BTW I'm not pro IEE, but feel that as they are the authors of the regs, they must have good test procedures in place and good reason why after all this time they decide to change fundamental things in the regs.

Or am I being naiive??

Maybe we are guinea pigs for life........