Supplementary bonding

[marksecond]

Hi, I've read through alot of threads regarding this subject but I'm still unsure.

1. Bathroom- Has a rad, sink, bath and thermostatic shower all fed by copper pipes that have a number of plastic push fit connectors. How should these pipes be bonded in this case?

Should I connect all of the above pipes with each other ie. the rad incoming and outgoing, hold & cold for sink, bath & shower?

Also I’ve been told that the metal legs of my fibre glass bath need to be bonded. Is this the case?

Should the radiator itself be bonded or is it the pipes that feed the rad that should be bonded? I've seen some clamps for sale that clamp directly to the rad.

I've read that the bonding should be connected to the cpc of circuits supplying that room. The only electricity in the bath room is the lighting which are SELV downlighters switched by a pull cord. Should the bonding cable be terminated inside the pullcord switch?

2. Do rads in other rooms in the house need to be bonded. ie living room? If so would you connect to the earth in a socket?


Hope I haven't asked too much in one go. Any assistance is appreciated

 

[JohnD]

Easy bit first:

2 - No.

1. Electricity can pass through the water in plastic pipes, but not very far. The dirty water in radiators is more conductive than the clean tap water. If yours are copper pipes with plastic joints, I suppose (there may be a learned article somewhere) that you will have to bond them at the copper where they enter the bathroom.

You do not have to bond the radiators themselves if you have bonded to the pipes; because the only way electricity can get into the bathroom and into the rad is through the pipes.

SELV must not be connected to earth, but I imagine your switch is at mains voltage and controls the supply to a transformer, so bond to the earth conductor of the lighting circuit. The switch is a convenient place.

Have you no shaver socket? An immersion heater? An extractor fan? a shower pump?

 

[Lectrician]

Depending on ceiling height, the lights and pull cord maybe outside the zones anyway

You dont have to bond any copper fed by plastic, or insulated by a plastic joint etc. You do need to bond any copper that enters the bathroom. Water plays no part in the rules for supp bonding.

Not sure on the SELV comment JohnD?? No one is going to bond the selv side of the tranny are they

 

[JohnD]

I hope not, but... SELV... Supplementary bonding... thought it best to mention. With ordinary lamps you can bond at the light fitting if you want.

As to plastic joints... I saw a tech bulletin a while ago that measured resistance of columns of water (clean/dirty) and I vaguely recall that it was high enough that a couple of metres of plastic pipe were OK, but joints weren't as the water could give (unreliable) continuity between the two lengths of copper.

 

[marksecond]

Thanks for your help.

Still not quite sure though with these plastic joints.

Would it make any difference if the pipes were copper with copper soldered joints? Does it make any difference if there is a better path to earth. In my bathroom, all of the pipes are copper with plastic joints so all have bad paths to earth and are at the same potential? Don't really understand fully

I dont have a shaver socket, shower pump or immersion heater in the bathroom. I've got a combi boiler downstairs so mains pressure is good and no need for a pump.

As you rightly say, the pull cord is at mains voltage with supplies a transformer for the SELV lights.

Thanks in advance for your help

 

[JohnD]

Pipes: Bond to the copper at the first bit, inside the bathroom, that you can reach. This is where any voltage coming in would be at its highest.

If they had soldered joints it wouldn't matter where you bonded to them, you could even bond in the airing cupboard if adjacent to the bathroom.

I am assuming you do not have an iron soil-pipe or lead waste pipes coming into the bathroom.

 

[marksecond]

No lead or iron waste pipes.

How about the metal legs of plastic bath?

 

[JohnD]

Unless they poke through the floor, they do not enter the bathroom from outside, and are not attached to anything that could introduce a voltage, so do not need to be bonded.

Same for metal soap dishes, coat hangers etc.

 

[RF Lighting]

coat hangers

 

[marksecond]

Thanks. It's just that a friend quoted from a Readers Digest Electrical Manual that said you should bond the metal legs. I thought it was a bit strange

 

[JohnD]

If it was a cast-iron bath, that would be one way of doing it. However you would already have bonded it through the metal pipes, so unless it had a lead waste pipe, it would not be in contact with anything that could introduce an earth or other potential.

 

[Taylortwocities]

Herewith one learned article from that Paul Cook bloke. Seems that tests have shown that tap water in a plastic pipe is a poor conductor of electricity.
Test showed that one metre of 15 mm diameter plastic pipe filled with tap
water has a resistance of 100,000 ohm. This equals 0.1 ohm per mm.
That means that a plastic joint (say 50mm?) between two lengths of pipe only introduces a resistance of 5 ohm and will not limit the fault current to safe levels. The article does say that a metre of plastic pipe would limit the current sufficiently.

Still awake? The full article is at http://www.iee.org/Publish/WireRegs...tumn_plastic_pipes_to_bond_or_not_to_bond.pdf

Personally, I'd bond a metal pipe in a bathroom if I was not sure of routing or how much plasic pipe was in the floor.

TTC

 

[JohnD]

Thanks, TTC, that must be the one I was thinking of.

 

[Taylortwocities]

...............a Readers Digest Electrical Manual that said you should bond the metal legs.................