Earth Bonding

[jlaspire]

I'm about to board existing wiring runs and want to make sure everything is in place before it's all done. Electrics are from above so will all be covered over and wont be able to change them.

The original earth bonding was taken from the shower fuse switch in the ceiling and then dropped down to the radiator tails and toilet. No earthing on the basin or bath as these are in plastic pipe. The radiator is also in plastic so can't understand why they bonded this and not the others.

Question is. is it safe to bond from the earth of the shower cable and also do items need bonding if plastic pipes are used anywhere on there run. Seems to defeat the object? If the tails up from the floor are copper do these need to be bonded if the rest is plastic?

Just to add the shower is connected direct to the main board in 6mm with a 32 amp rcd.

Regards

 

[PrenticeBoyofDerry]

I'm about to board existing wiring runs and want to make sure everything is in place before it's all done. Electrics are from above so will all be covered over and wont be able to change them.

Are the cables in the permitted safe zones? If not best not cover them up until they are correctly installed.

The original earth bonding was taken from the shower fuse switch in the ceiling and then dropped down to the radiator tails and toilet. No earthing on the basin or bath as these are in plastic pipe. The radiator is also in plastic so can't understand why they bonded this and not the others.

So this is a bath/shower room and you are actually talking about supplementary bonding?

Question is. is it safe to bond from the earth of the shower cable and also do items need bonding if plastic pipes are used anywhere on there run.

I think a little more detail would be required from you, this is supplementary bonding, not main earth bonding, they are very different!

Seems to defeat the object? If the tails up from the floor are copper do these need to be bonded if the rest is plastic?

You would need to prove via testing that they do not require bonding

Just to add the shower is connected direct to the main board in 6mm with a 32 amp rcd.

32A RCBO do you mean? Providing the shower requires 32A or less, then that is fine, but that would not mean that supplementary bonding can be excluded from the room without proving it is not required.

 

[jlaspire]

Thank you for the reply.

Currently the only things that were bonded were the shower (from the pull cord fuse switch), lighting circuit and then down to the radiator. All together with no run back to the main board. I'm just doing a change over and adding a bath as it was a wet room before.

All water mains were in copper but the last installer changed them to plastic for the last run. I will be using this but will add copper at the ends for the tails to the sink and bath. Also the radiator is being changed to a towel radiator but the main piping for this is also in plastic!

 

[ericmark]

The rules on bonding changes according to which edition of BS7671 the house is wired to. The whole idea of bonding is to prevent a fault in one room being transmitted to another room through metal work in the house. So if for example the dog knocks over a standard lamp and the bulb smashes and rests on a radiator in living room it will blow a fuse rather than transmit the fault to other rooms where the occupants would have no idea the lamp had been broken.

However to bond does not mean connect to earth although normally there will be an earth connection it means making sure all metal work is at the same voltage like the bird on electric wires if all at same voltage then no shock.

Bonding can also cause dangers a good example is the shaver socket with has no connection to any other electric item or bonded item it is the isolation which makes it safe.

Additives in central heating water means it conducts better than potable water but with plastic pipes and RCD protection there is no need to bond even when the short lengths in view are metal to look nice. But plastic connectors often only separate pipes by a few millimetres so to cross bond pipe to pipe is the norm.

Under 2008 regulations every electrical item in the bathroom needs RCD protection including the lights. It is very easy to miss something when writing on a forum and really some one needs to see this not just written on forum.

 

[jlaspire]

Hello. Sorry yes all the electrical items in the bathroom are rcd protected. This is a council install before and a new rcd box is fitted separate to the rest of the house.

 

[EFLImpudence]

yes all the electrical items in the bathroom are rcd protected.

Then -

IF
All Main Protective Bonding is in place and all extraneous-conductive-parts in the bathroom are effectively connected to the Main Earthing Terminal
AND
All disconnections times are met -

Supplementary bonding may be omitted.

 

[PrenticeBoyofDerry]

Currently the only things that were bonded were the shower (from the pull cord fuse switch), lighting circuit and then down to the radiator. All together with no run back to the main board. I'm just doing a change over and adding a bath as it was a wet room before.

That could be all that was required to be supplementary bonded and there would normally be a path back to earth via the circuit protective conductors of the equipment/accessories of the lighting/shower.
It is likely that the shower isolator is not fused but there may be an indicator light on it.

All water mains were in copper but the last installer changed them to plastic for the last run. I will be using this but will add copper at the ends for the tails to the sink and bath. Also the radiator is being changed to a towel radiator but the main piping for this is also in plastic!

There would be no need to bond the pipework were plastic inserts have been made, but if you have metallic pipework within the room that is continuous back to the mains water then it is likely that it would be required.
It is now a requirement that all electrical items within bathr/shower/wet rooms are protected by 30mA RCD, this often then means supplementary bonding of pipework can be omitted.(refer to the conditions named in the above post)

 

[jlaspire]

From what I can see they have used the shower supply earth as the main earth run this has then been taken to the lights and then down to the radiator. Think possibly the central heating may have been changed at a later date so the radiator would have been also bonded but has now been changed to plastics so is no longer needed.

As all the pipework within the bathroom is now broken and in plastic for the final runs I can see why they have not been bonded. I was always under the impression that the main earth run should go back to the board with no breaks between each service so was surprised to see it from the shower earth.

 

[ericmark]

There are a number of things which make me wonder how much you under stand like 32A RCD.

Yes you can get a 32A RCD but not very common in the main the items marked 32A are MCB's.

It was only in 2008 that we started to put RCD's on the lights and before saying bonding may be omitted do check the lights in the bathroom are RCD protected at 30mA.

Houses wired using an earth rod (TT) have had RCD's for years but these are normally 100mA not 30mA so you do need to check if the RCD for the lights is 30mA not 100mA before omitting earth wires.

Also remember any work in the bathroom electrics comes under Part P you talk about council involvement so likely it will need inspecting. Also burying cables under flooring may mean the cables are de-rated.

 

[EFLImpudence]

From what I can see they have used the shower supply earth as the main earth run this has then been taken to the lights and then down to the radiator.

This will be supplementary bonding (joining together) - not earthing.

Think possibly the central heating may have been changed at a later date so the radiator would have been also bonded but has now been changed to plastics so is no longer needed.

If you are correct then this bonding should be removed.
Measurements need to be taken to determine if this is the case.
The connection between the shower CPC(earth wire) and the lighting CPC can be left as it will have no detrimental effect.

As all the pipework within the bathroom is now broken and in plastic for the final runs I can see why they have not been bonded.

That could be correct.
Again, measurements are necessary.

I was always under the impression that the main earth run should go back to the board with no breaks between each service so was surprised to see it from the shower earth.

The CPCs will but the bonding does not have to.

 

[jlaspire]

Thanks for the replies.

Have checked and all the central heating is now in plastic just the last bit of the tail runs.

If the lights and the shower go back to the main board on single runs as this was a new installation to the rest of the house with a separate board how come they still join the lights and the shower together with an earth if they both go back or is this if one has a fault?

 

[EFLImpudence]

So that there is no potential difference between the two.

As said, it is not earthing but bonding (joining together).

 

[jlaspire]

So that there is no potential difference between the two.

As said, it is not earthing but bonding (joining together).

right kind of see what you mean. Good job I'm only putting the cables in place! Thanks for your help!