Supplementary bonding – what’s the big deal ?

[Curious J]

Dear all

This may be a bit of a long post and I have looked through the forum for relevant posts in the past, but, to be blunt, this supplementary bonding thing seems to be a bit of a minefield and it’s hard to pick out the information I need from the posts. So apologies in advance for the length of my post and if my questions have been answered elsewhere.

A little background.

We’ve rented a house while we look for another plot of land to build a new house. The electrician we used for our previous build went to great lengths to install, what I now know to be, supplementary bonding in our bathrooms. I thought he was going a bit over the top with the bonding but after spending a couple of days reading posts on this forum, I can see why he needed to bond the bathroom and en-suite (due to current regulations regarding safety in Special Locations).

I’ve noticed in the house that we’re renting there seems to be no supplementary bonding at all (other than the kitchen). There is a main bathroom, an en suite, a downstairs loo, a kitchen and a utility room.

The main bathroom has a bath, basin, WC and radiator. There is also a shaver socket, ceiling light, pull cord switch and a down light in a cabinet (a kitchen type cabinet) that is directly above the basin. The cabinet and light are approximately 850mm above the basin and the light is connected to a 1.5mm cable that disappears into the wall behind the cabinet. This down light is live, but I can’t see a transformer so I guess it’s fed with 240 volts. None of the pipe work (it’s all copper) that is visible has any bonding to it.

The en suite has a shower (not electric), basin, WC and radiator. Again there is a shaver socket, ceiling light, pull cord switch and a live down light in a cabinet 850mm above the basin (similar to the cabinet in the main bathroom). The wiring of this down light is the same as the main bathroom. And all the visible pipe work (copper) lacks any bonding.

The utility room and down stairs WC lack bonding too, but I’ve read in other posts that it is not required in these rooms as there is no bath or shower. The kitchen does have bonding connected to the copper hot and cold taps, but I’m guessing that this bonding is part of the Main Bonding as the earth cable (4mm I think) disappears into the wall and I assume goes back to the consumer unit. There is no MET by the consumer unit or in the outside cupboard where the meter is installed, so I’m guessing all the earth cables are connected together inside the Consumer Unit.

OK to my questions, in no particular order …

Question 1
The house appears to have been built in 2001 (there is a sticker on the Consumer Unit stating it was installed then). As the Part P regulations came out in 2005, should this house have supplementary bonding in the bathroom and en suite or is it exempt ?

Question 2
The down lights above the basins in the bathroom and en suite worry me, especially since my wife is pregnant. They are of the type that you would see in a kitchen ceiling, ie not sealed either around the bulb (this is held in by a metal ring) or inside the cabinet (it’s possible to open the cabinet and touch the part of the down light that would ordinarily be hidden in the ceiling). Can these down lights be that close to a basin and unprotected ?

If not, how can they be made safe ?

Question 3
Supplementary bonding is not designed to make a circuit trip out in the event of a fault, it’s designed to bring any exposed metal like pipe etc work to a similar voltage. For example. Without bonding, if for some reason the cold tap to the basin was to become live, touching the hot tap (that wasn’t live) would result in an electric shock. But with bonding, both taps would become live (should the same fault mentioned above occur), but because the hot and cold taps are connected by the bonding, there would be no difference in voltage between the two taps and no one would get a shock. Do I understand how supplementary bonding works correctly ?

Also, if, say the hot tap was to become live, why wouldn’t the circuit trip out at the consumer unit ? Surely that’s what the MCB’s are designed to do.

Question 4
If supplementary bonding is required to be added to the bathroom and en suite. All that is required is a single earth cable (4mm or bigger) to be connect to all the pipe work and then be connected to the earth cable of the light fitting or shaver socket ?

Question 5
SELV – what is this ? I’ve read in various places that electrical fittings can be placed in Special Locations without additional bonding if they are SELV. Could the down lights in the cabinets above the basins be SELV devices and how could I check ?

Question 6
Assuming that supplementary bonding is required, that it hasn’t been installed, that the electrician who has inspected the electrics hasn’t checked the bonding exists and that no accidents regarding an electric shock occur. What’s the big deal ?

I’m not trying to be awkward, but who would care about the lack of bonding in my bathrooms, the Health and Safety Executive, NICEIC ?


I would be grateful for any comments from the members of the forum that would help me sort out and understand a bit more about bonding in special locations. Thanks for taking the time to read through this post.


John.

 

[Steve]

1. part p has nothing to do with supplementary bonding.

2. the downlights on the ceiling needn't be protected, if they are 8 foot up, but an IP rated light needs to be installed inside the cabinet.

3. by connecting all the pipework and circuits together, you are creating an equipotential zone, where any voltages entering the bathroom via pipes or circuits are equal across all the exposed parts. The voltage could be induced by a circuit, but because it is spread across all ECPs, it isn't dangerous. If, however, it is being leaked from a circuit, it will trip an RCD if connected. It may not trip an MCB unless it is a short circuit and many amps are flowing.

4. ALL circuits entering the bathroom need to be bonded, and all exposed metalwork entering the room, including the radiator.

5. SELV is Safe Extra Low Voltage, fed from a safety isolation transformer. SELV sources are generally 12 or 24 volts. If your bathroom lights are 12 volts, then they are probably fed from an SELV tx.

6. ?

 

[davelx]

6) Depends on who is killed or injured when the fault eventually happens. This is the same argument as "I never wear my seat belt and I've not had an accident"

 

[ricicle]

5. SELV is Safe Extra Low Voltage

Seperated extra low voltage

 

[Curious J]

Thanks guys, I appreciate your time and help.

Crafty

1. part p has nothing to do with supplementary bonding.

I guess Supplementary Bonding is part of the Building Regulations then.

2. the downlights on the ceiling needn't be protected, if they are 8 foot up, but an IP rated light needs to be installed inside the cabinet.

They’re definitely no more than 850mm above the basins and they’re not IP rated devices.

3. by connecting all the pipework and circuits together, you are creating an equipotential zone, where any voltages entering the bathroom via pipes or circuits are equal across all the exposed parts. The voltage could be induced by a circuit, but because it is spread across all ECPs, it isn't dangerous. If, however, it is being leaked from a circuit, it will trip an RCD if connected. It may not trip an MCB unless it is a short circuit and many amps are flowing.

I think I need to figure out the difference between MCB’s and RCD’s. The Consumer Unit in the house is a split load type, with the ring mains on the RCD side and the lights / alarm on the MCB side.

4. ALL circuits entering the bathroom need to be bonded, and all exposed metalwork entering the room, including the radiator.

None of the pipe work is bonded in either of the bathrooms.

5. SELV is Safe Extra Low Voltage, fed from a safety isolation transformer. SELV sources are generally 12 or 24 volts. If your bathroom lights are 12 volts, then they are probably fed from an SELV tx.

The lights in the cabinets are 240v. I know this as I tested them with a multi meter.

6. ?

I don’t particularly want to get anyone in any trouble. But I think (if I’m right about the bonding being a regulation) then the people to speak to would be my local Building Control Office at the Local Authority. I’d much rather the land lord / letting agent just sorted the issues.

Davelx

6) Depends on who is killed or injured when the fault eventually happens. This is the same argument as "I never wear my seat belt and I've not had an accident"

I can see what you’re saying, it’s only a matter of time before someone got a belt. If not me or the misses then maybe the next tenants.


Thanks again. If anyone else has any comments I'd be grateful.

John.

 

[DESL]

I guess Supplementary Bonding is part of the Building Regulations then.

No - it's part of BS7671 - IEE wiring regulations 16th Edition

 

[winmill]

with ref to qu 4:

4. ALL circuits entering the bathroom need to be bonded, and all exposed metalwork entering the room, including the radiator.

if this is the case the earth conductor in the electrical circut returns to the earth terminal in the consumer unit, so why is it that the 4mm y/g bonding conductor must not be run back to the earth terminal in the consumer unit?

 

[RF Lighting]

It's irrelevant now. An entire set of new regulations has been issued and subsequently ammended since this thread was last posted on.

 

[xr4x4]

It's irrelevant now. An entire set of new regulations has been issued and subsequently ammended since this thread was last posted on.

Could you post where?

As I've always been a bit confused as to what's what.

Is bonding earthing metal pipes together but not connected to anything else?

And earthing is normally incoming water, gas and oil to the met?

 

[Spark123]

RF is just saying that the rules have changed, the original post was in 2007 when the 16th edn regs were in force.
Now the 17th edn (BS7671:2008 amd2:2011) are in force so what is written in the posts above is no longer the case.

 

[EFLImpudence]

Could you post where?

The original post is from 2007 - 16th

Is bonding earthing metal pipes together but not connected to anything else?

Bit confusing - if you delete 'earthing' from your statement that would be supplementary bonding.

And earthing is normally incoming water, gas and oil to the met?

That's main bonding.

 

[xr4x4]

RF is just saying that the rules have changed, the original post was in 2007 when the 16th edn regs were in force.
Now the 17th edn (BS7671:2008 amd2:2011) are in force so what is written in the posts above is no longer the case.

Yeah, I know.

Does anyone know where I could read up on the current regs?

 

[EFLImpudence]

BGB

 

[RF Lighting]

It's irrelevant now. An entire set of new regulations has been issued and subsequently ammended since this thread was last posted on.

Could you post where?

Could I post what where?

As I've always been a bit confused as to what's what.

Don't worry it confuses most people including many electricians

Is bonding earthing metal pipes together but not connected to anything else?

No.

Bonding is bonding. Earthing is earthing. They are two entirely different things carried out for entirely different reasons.

Bonding is connecting together all the things which are in the same equipotential zone, and might be at different potentials to each other so they are maintained at substantially the same potential. The things you need to bond will include some, all or none of the following:
Incomming metallic water pipes
Incomming metallic gas pipes
Incomming metallic oil pipes
Structural steel
Electricity suppliers earth terminal
Lightning protection
Cast iron soil pipes
Copper or lead drain pipes
Central heating pipes
Hot water pipes
Shower circuits
etc...

and just because it's on the list does not mean it will need bonding in every situation.

And earthing is normally incoming water, gas and oil to the met?

No. Earthing is connection of the exposed-conductive-parts of an installation to the main earthing terminal of that installation.

An exposed-conductive-part is a conductive part of equipment which can be touched and which is not normally live, but which can become live when basic insulation fails.

You would earth a metallic socket front or metal clad fuse board as the failure of basic insulation would cause the equipment to come live. If the equipment is earthed then a large current will flow from line to earth causing the operation of the protective device.

 

[xr4x4]

Thanks for that, still blows my mind tho...

I'm guessing it's a lot easier these days with rcd protection. I.e only main bonding.