Bathroom Equipotential Bonding

[callwild]

I am trying to get clear advice on what supplementary bonding is required in my bathroom.
My house is 30 years old and I have just renewed the bathroom suite and added an electric shower.
Originally the electrics in the bathroom consisted of a ceiling light and a wall fan heater. There was no supplementary bonding, only the copper water pipes bonded to earth near the consumer unit.
Now I wish to add correct supplementary bonding to make the installation safe and legal but appear to get conflicting advice.

This link appears to show the bonding only to the metal pipes
http://www.iee.org/Publish/WireRegs/EarthingPlasticPipes.pdf


While this link shows all the bonding connected via a seperate earth cable.
http://www.diydoctor.org.uk/projects/bondingbathroom.htm

which is correct?

The first iee link also says the earth bonding should be made to the earth of protective conductors of class 1 and class 2 equipment within the bathroom and NOT run back to the main earth.
Whereas one electrician I asked recommended running the earth cable back to the main earth near the CU.
Again which is correct? Is connecting all the supplementary bonding back to the earth connection in the shower unit sufficient?

I presume I should also find a way of connecting the fan heater earth to this supplementary bonding ciurcuit and pipes although it is on a wall on the opposite side of the room.

 

[pdcelec]

All extraneous conductive parts require bonding together with any equipment within the zones using 4mm2 cable.

 

[Spark123]

The iee site gives the clearest advice, i.e. supplementary bond all pipework together and supplementary bond from the pipework to the circuit protective conductor of all class 1 and class 2 electrical equipment in all of the zones. You should not run an earth back to the CU. For your fan heater, if it is in one of the zones it should be also be supplementary bonded.

 

[callwild]

Thanks, that confirms what i thought. It was the iee site showing only bonding to the pipes and the advice about running it back to the CU which was confusing me.

 

[ban-all-sheds]

While this link shows all the bonding connected via a seperate earth cable.
http://www.diydoctor.org.uk/projects/bondingbathroom.htm[/QUOTE]
Don't bother with them - they are a waste of space - their "interpretation" of Part P shows that they can't actually read.

Whereas one electrician I asked recommended running the earth cable back to the main earth near the CU.

The trouble is that many electricians are driven by superstition and fear - they waggle their hands and say things like "Woooohhh, bathrooms", and come out with ideas based on ignorance of the reason for supplementary equipotential bonding.

 

[plugwash]

running an extra earth back to the CU can make sense in some situations.

the most obvious one i can see is if a shower cable was unusually long and the lighting cable to the room was unusually short meaning that the lighting cable took more than its fair share of the fault current in the case of a fault with the shower cuircuit.

remember by bonding together mutliple cuircuits you are creating paralell earth paths. whilst this is not usually a problem it can require more carefull thought in ususulat situations.

 

[user56565]

running the earthing back to the CU is not bad, just unnecessary. if you are bonding to a circuit's earth conductor, then you have already made this connection to the CU/MET anyway. so such a connection is not infact dangerous. its unnecessary as the main reason supplementary bonding is present, is to maintain all 'earths' in the bathroom at the same potential. connecting to the CU/MET doesn't achieve this.

 

[SwindonSpark]

Try this link: -

http://www.niceic.org.uk/downloads/NL139supp.pdf

 

[callwild]

Confused again.
Ban-all-sheds wrote

Don't bother with them - they are a waste of space - their "interpretation" of Part P shows that they can't actually read.

with regard to the DIYdoctor link
http://www.diydoctor.org.uk/projects/bondingbathroom.htm
However the diagram on this link shows all the pipes and electrical appliances connected by earth cable as is supposedly suported by the other answers here.
The IEE link
http://www.iee.org/Publish/WireRegs/EarthingPlasticPipes.pdf
shows the bonding only to the pipes and allowing the pipes to make the earth connection circuit.
So my original question still doesn't seem to have been answered by a consensus.
I can understand that the earth to the appliance is routed to the CU earth so no extra cable is required for that.
But my understanding about the equipotential bonding would be that as the water pipe to the shower takes a different route from the water pipes to the bath then they would have a different resistance back to the main pipe earth by the CU therefore a direct earth cable between the two would remove this difference.
Is this correct.

Stuart

 

[ban-all-sheds]

The IEE link shows the bonding only to the pipes and allowing the pipes to make the earth connection circuit.

This may be the reason for the confusion. It's not an "earth connection circuit", it's an equipotential bonding circuit. The requirement is that the protective conductors of all power and lighting points within the zones must be supplementary bonded to all extraneous-conductive-parts in the zones.

Provided the pipework has soldered joints, there is no need to have a cable connecting multiple places on the pipe network to each other. If you look at the IEE diagram you'll see that the bonding cable from the shower is connected to the shower water pipe, both bath supply pipes and the bath waste. The bonding cable from the shaver socket is connected to the both basin supply pipes and the basin waste. The only connection specifically between two pipes is the one by the rad linking the CH pipes to the water supply pipes.

 

[callwild]

Thanks again
That clears things up. Its back to what I originally thought and understood .

What about compression joints? When I test the continuity they seem OK.

Stuart

 

[slippyr4]

Bathroom supplementary bonding is intended to put all metal in the bathroom at as near to equal potential (read equal voltage) to each other.

In the event of an earth fault in a bathroom appliance, if that appliance and some other piece of metal are individually eathed way back to the CU then there will be a (possibly significant) potential difference between the items, and a shock may result. The localised equipotential bonding means that these metal things in close proximity are guaranteed to be very close to the same potential to each other, and thus the risk and effect of a shock is significantly reduced.

Now, if you extrapolate that a bit further and consider a situation where a bathroom has an electric shower, a cast iron bath plumbed with plastic pipes, and the local equipotential zone having it's own connection to the earth point at the CU.

Then consider what would happen if somehow the earth connection between the electric shower and the bath was damaged or broken- the batch is earthed to the CU, the shower is faulty, and you get a shock. Had the local equipotential bonding not been linked to the CU, this would not of happened.

I hope this contrived example illustrates why a) you don't need to and b) how it actually might not even be a good idea to, separately earth the local equipotential.

PS, i'm not a qualified spark but I am a qualified electrical engineer.

 

[callwild]

So as I understand it now it is fine for the basin, Sink, toilet to be bonded to the pipes but not directly to each other as they are only spaced within a metre of each other along the same pipe. But the shower and its water pipes must be bonded to these main water pipes as well. Good I was wondering for a while how to hide all the extra wires running around the bathroom connecting thiongs and it didn't make sense when they were only 50cms apart .

Wall fan heater however. This has always been in my house but on closer inspection it does not have an earth so I can not make asupplementary bond. Should it therefore be in a bathroom at all ? It is situated within zone 2 with a pull cord.

stuart

 

[user56565]

slippyr4

the problem with your analysis is that it's assumed on the earth connection being somehow damaged or broken. you could apply this thinking to any circuit, as in 'what if this cable broke?' etc., and you could end up with hundreds of possible dangers. the liklihood of broken cables is reduced by the installer by either mechanically protecting, or using thicker more resilient cables. the risk of cables being damaged would only be significant if there was negligence on behalf of the installer.

secondly, the shower earth is linked to the MET. the potential difference between the bath (linked to MET) and the shower would be very low.

thirdly, the bath wouldn't have been earthed in the example anyway, as it does not introduce an earthy potential of its own into the equipotential zone.

you are correct in the sense that it's unwise to introduce earth potentials into the bathroom unneccessarily ie by linking the MET to a metal shelf or something similar.

callwild, if the fanheater is double insulated, it doesn't need an earth as such. i would ignore it.

 

[mapj1]

If the fan heater goes to a fused connection unit or similar, where an earth is present, in the same way as a light switch earth, then strictly that should be bonded in, either there or as near as possible- earthed screws on the box front and all that..
However, unless you are redecoating or can do it in an easily hidden way, I'd leave it for now.
Compression joins are only OK, if they are good for the fault current, which on a shower circuit could be a few 100s of amps until something blows. As some plumbers use plumbers mait, or PTFE tape, to mitigate against scratched olives leaking unless you are sure of a good metal-metal join, then strictly these should be bonded accross. In practice I suggest its OK, if, its not full of PTFE tape, its not green and furry, and there is no hint of plumbers main being used. Others will say if in doubt bond across the compression joins.