Supplementary bonding in bathroom

[pertinky]

Hey guys,

I'm trying hard to understanding earthing and bonding for my own benefit, and I get the purpose of it in a bathroom from a safety point of view (equipotential bonding) however I'm not entirely clear how to work out whether or not it is required for my bathroom refit so I can get the floor down.

The old bathroom layout had a cylinder in the corner, with electrics situated next to the tank (spur for immersion and heating motor valves).

Copper pipe work came in from downstairs under the bath, across the room to the cylinder (so the copper pipe was exposed). This was clamped to the showers cold supply with an earth wire running back to the fuse board.

The cylinder has been moved outside the bathroom, but the pipework still largely runs in the same place with a slight modification in that the hot and cold for the bathroom and the last leg of the flow/return for the CH is now out of plastic (I was left two sets of isolators in the floor to work off). The vertical pipe above floor level for the towel rail is also copper for atheistic reasons only although this could be replaced with plastic with a pipe shroud.

I have, for the sake of continuity, moved the old earth clamp down on to the cold supply for the bathroom

The consumer unit is only RCD protected for socket rings. I am planning on getting a sparky to add a new RCD protected lighting circuit specifically for the bathroom/ensuite as we're also replacing downlighters and moving them (no zoning issues, ceilings are 2.6m high). As I understand this is a requirement for lower ceilings, but might be a belt and braces approach for high ceilings like ours.

We are planning on installing backlit mirrors in both rooms so I guess I can just have them running off the new lighting circuit w/ RCD protection, or I can take a spur off the upstairs ring (next to cylinder) and fit a 5A FCU which will also have RCD protection.

I see diagrams connecting all lights, appliances and pipework together and was wondering if this is always necessary. It certainly wasn't done like this when I removed the bathroom suite.

I'm also a bit cautious as to there is no bonding in the pipework at the new cylinder location.

 

[John D v2.0]

Once you have got RCD protection on all circuits serving the bathroom including lighting, ensured all main bonding in place especially water and gas if the enter the house in metal, and all the circuits meet the correct disconnection times then no need.
If no to any of the above, then you need to bond all metallic parts which may introduce a potential into the bathroom together with the cpcs of all circuits entering the bathroom.
But the latter two you need to fix anyway, and the former is a requirement for all new concealed wiring and sockets.

 

[pertinky]

Once you have got RCD protection on all circuits serving the bathroom including lighting, ensured all main bonding in place especially water and gas if the enter the house in metal, and all the circuits meet the correct disconnection times then no need.
If no to any of the above, then you need to bond all metallic parts which may introduce a potential into the bathroom together with the cpcs of all circuits entering the bathroom.
But the latter two you need to fix anyway, and the former is a requirement for all new concealed wiring and sockets.

No RCD protection on lighting circuits currently, although I plan to fix this by putting an RCD fused spur in the attic above the bathroom/ensuite to feed the new lights

We dont have gas; its an oil fired boiler, so the cooker is running off electric as well.

As far as I can see, there are earths running to just above stop cock, and from the consumer unit, and from the supply to the MET. Is this "main bonding"?

 

[Taylortwocities]

We dont have gas; its an oil fired boiler,

Perhaps, but the oil feed pipe that enters the building should be bonded, in the same way as a metallic water or gas pipe.

 

[EFLImpudence]

Do you actually have any Exposed-Conductive-Parts in the bathroom (now the cylinder has gone)?

That is metal parts of electrical equipment which might become live in a fault.

 

[pertinky]

Perhaps, but the oil feed pipe that enters the building should be bonded, in the same way as a metallic water or gas pipe.

Just checked, it is. Its actually bonded to the water pipe was difficult to see with access

 

[pertinky]

Do you actually have any Exposed-Conductive-Parts in the bathroom (now the cylinder has gone)?

That is metal parts of electrical equipment which might become live in a fault.

I cant think of any....all the pipework to shower/basin/bath/radiator is now plastic. The shower is unvented so no electrics there. Do the downlights count? they are above 2.25m so unreachable without ladder.

We are planning on putting in a backlit mirror off the lighting circuit so theres likely going to be a switch in the mirror. Would this count as exposed? I suspect it would have a built in shaver socket.

Alot of the pipework under the floor is still copper, but obviously it wont be accessible when the subfloor goes down.

 

[EFLImpudence]

Do the downlights count?

They count - but do they have accessible earthed metal parts (some do) which might become live during a fault - and could you touch any metal pipes at the same time as touching them?

they are above 2.25m so unreachable without ladder.

Not really accessible, then.

We are planning on putting in a backlit mirror off the lighting circuit so theres likely going to be a switch in the mirror. Would this count as exposed?

I doubt it will have any exposed metal parts

I suspect it would have a built in shaver socket.

...but it won't be metal, will it?

Alot of the pipework under the floor is still copper, but obviously it wont be accessible when the subfloor goes down.

...but are they connected to metal taps.

The problem arises when you could touch a faulty electrical item at the same time as an earthed metal pipe/tap etc.
If that is not possible in your bathroom then supplementary bonding is not required.

Some supplementary bonding may be required between accessible metal pipes/taps etc. (extraneous-conductive-parts) but this can only be determined by measuring the resistance between them.
Indeed, they might not be connected to any earth at all, or they may be connected effectively enough by their own joints so that no further bonding is required.

 

[pertinky]

@EFLImpudence

We'll be replacing the downlights, but have not picked any yet. You wont be able to touch the lights and the pipes at the same time.

I would have thought maybe that the backbox of the mirror would be made out of metal though and might need to be earthed (a bit like the backbox in a normal switch/socket)

The taps would be connected to plastic above the floor (the plastic/copper joins are below the floor). The copper pipe emerges from outside the room in to the new airing cupboard housing the cylinder. You cannot reach from there to anything metal in the bathroom

These pipes might need to be bonded together then (my sparky can probably test resistance between them when he's next here). Theres a few of them (inlet/outlet/overflow for cylinder, upstairs/downstairs/hot water zones)

 

[EFLImpudence]

We'll be replacing the downlights, but have not picked any yet. You wont be able to touch the lights and the pipes at the same time. At best they will be accessible from the loft.

Ok.

I would have thought maybe that the backbox of the mirror would be made out of metal though and might need to be earthed (a bit like the backbox in a normal switch/socket)

Yes, but will you be able to touch it?

They would be connected to metal taps via plastic. No copper would be above ground.

No extraneous-conductive-parts, then so the taps must not be bonded.

The copper pipe emerges from outside the room in to the new airing cupboard housing the cylinder. These might need to be bonded together then (my sparky can probably test resistance between them when he's next here)

Yes.

You seem to be missing the point.
The danger is touching a live (because of a fault) metal electrical part AND an earthed metal part (e.g. pipe) at the same time, but only in the bathroom.
What happens elsewhere is irrelevant.

From what you say it would appear that you have no simultaneously accessible exposed-conductive-parts nor extraneous-conductive parts in the bathroom so there is actually nothing to which you need - or can - fit supplementary bonding.

 

[pertinky]

@EFLImpudence Thanks I've understood it now. It would be a case of you completing the circuit in that scenario.

Why is it only a problem in the bathroom? Is it because of the conductivity of water?

Whats the difference between exposed and extraneous in this context?

Lastly, I'm trying to figure out why we had this earthing in the first place. Presumably because inside the old airing cupboard (which was in the bathroom) you had both extraneous conductive parts in the pipes, an exposed conductive parts in something like the immersion heater or the motorized valves controlling the zoning? Did I get them the right way around?

 

[EFLImpudence]

@EFLImpudence Thanks I've understood it now. It would be a case of you completing the circuit in that scenario.

Yes.

Why is it only a problem in the bathroom? Is it because of the conductivity of water?

It is because of wet naked bodies and, more particularly being stood in/on water on the floor.

Whats the difference between exposed and extraneous in this context?

An exposed-c-p is the touchable earthed metal parts of electrical equipment.
An extraneous-c-p is metal that is not part of electrical equipment which might introduce a potential from outside of the location. If it definitely won't introduce a potential, i.e. not connected to anything, then it is not an extraneous-c-p even though it is metal.

Lastly, I'm trying to figure out why we had this earthing in the first place. Presumably because inside the old airing cupboard (which was in the bathroom) you had both extraneous conductive parts in the pipes, an exposed conductive parts in something like the immersion heater or the motorized valves controlling the zoning?

Yes, although inside a cupboard does not really count.
Plus - a lot of electricians do not fully understand and treat specific instructions (which they take out of context) as blanket requirements.

As I said, these pipes in the airing cupboard are likely connected together by their own joints so that a piece of wire between them is not really necessary.

Did I get them the right way around?

You did although the valve will be all plastic and so have no exposed-c-p.

 

[winston1]

No RCD protection on lighting circuits currently, although I plan to fix this by putting an RCD fused spur in the attic above the bathroom/ensuite to feed the new lights

Seems rather a silly place to put it. Inconvenient when it trips. Also you don't need a "fused" spur if on the lighting circuit, just an RCD which would be better situated next to the CU feeding the whole lighting circuit that feeds the bathroom.

 

[pertinky]

Seems rather a silly place to put it. Inconvenient when it trips. Also you don't need a "fused" spur if on the lighting circuit, just an RCD which would be better situated next to the CU feeding the whole lighting circuit that feeds the bathroom.

The bathroom is on the upstairs radial, and my CU is about 17 years old so its only got RCD protection on sockets.

If I wanted to RCD protect all the lighting as well then thers an additional cost of new CU + sparky however I just need to protect the bathroom.

Could I not spur off the existing lighting circuit and fit an RCD there instead? I would have preferred to have it at the CU but I dont really want to replace the entire thing just yet we've only just moved in!

 

[JohnW2]

If I wanted to RCD protect all the lighting as well then thers an additional cost of new CU + sparky however I just need to protect the bathroom.

Not necessarily - you could just install an RCD close to your CU which protected the whole of the lighting circuit which supplies the bathroom.

Could I not spur off the existing lighting circuit and fit an RCD there instead? I would have preferred to have it at the CU but I dont really want to replace the entire thing just yet we've only just moved in!

You could - but, as has been said, in the loft is not the ideal place for an RCD which might (albeit very occasionally, if ever) need to be reset. As above, there's no reason I can think of why you could not protect the whole lighting circuit with an RCD close to (but separate from) the existing CU.

Kind Regards, John