17th Edition - Bonding confusion

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Hi,
I'm a little confused by the bonding requirments.

I'm building an extension, which will have an ensuite.
I'm currently doing the plumbing in the ensuite, which is mostly plastic but copper to the radiator and towel rail where the pipework can be seen.
As a result do I need to run an earth cable to each radiator/towel rail and the copper pipes under the tap, and bond them back to the consumer unit?

All power circuits in the bathroom will be protected by an RCD.

Thanks
 
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I'm currently doing the plumbing in the ensuite, which is mostly plastic but copper to the radiator and towel rail where the pipework can be seen.
As a result do I need to run an earth cable to each radiator/towel rail and the copper pipes under the tap, and bond them back to the consumer unit?

No.
 
So no bonding will be needed in the bathroom then?

I assume its worth bonding the boiler though and the radiators where theres a large section of the system connected with copper pipe?
(boiler is moving into utility room as part of the extension)

Thanks :)
 
No supplementary bonding in the bathroom if all extraneous-conductive-parts have protective equipotential bonding conductors (correctly sized) connecting them back to the MET (water, gas, LPG, oil, structural steel, cast iron soil pipe....anything which can introduce a potential from outside of the equipotential zone (your house)).
All circuits protected by an RCD with a maximum rating of 30mA.
All circuits comply with the requirements for automatic disconnection according to 411.3.2:

TN systems
<=32A - 0.4s
>32A - 5s

TT systems
<=32A - 0.2s
>32A - 1s
 
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I assume its worth bonding the boiler though and the radiators where theres a large section of the system connected with copper pipe?
(boiler is moving into utility room as part of the extension)

No need to. Water and gas (or oil, lpg etc) should be bonded.
Also no need to bond the radiators.

I do, however, cross bond under a boiler (set in my ways?) though the glanding plate should really connect all pipework together anyway.
 
I do, however, cross bond under a boiler (set in my ways?) though the glanding plate should really connect all pipework together anyway.

There never has been a need for this.

Furthermore, there is no such thing as 'cross bonding'.
 
I do, however, cross bond under a boiler (set in my ways?) though the glanding plate should really connect all pipework together anyway.

There never has been a need for this.

Furthermore, there is no such thing as 'cross bonding'.

OK, supplementary bonding then, cross bond being a term just a term used (by many) but then again you knew that and was just being pedantic!

I've seen many older electricians do this and instruct me to do it under my apprenticeship (late 15th edition).
One thing that surprises me is I still see it in many new houses.
 
You're absolutely right, GaryMo, I was being pedantic. But I have a reason. (This is not aimed at you, by the way.)

The majority of sparks I encounter daily do not understand the basic principles of earthing and bonding and frequently invent their own terminology, or simply repeat what their equally ignorant supervisors told them.

So, you then get sparks telling people to earth things they ought to bond to, to bond things that should be left well alone and to 'earth-bond', which is a nonsensical term.

On courses we have to be absolutely pedantic, because unless delegates use the correct terminology they will help perpetuate the ridiculous situation that we have. That situation is a trade which wants to be respected - and paid accordingly - for its superior technical knowledge and yet is largely unwilling (or unable) to grasp the fundamental principles of safe electrical installation design.

The fact that you see unecessary bonding in brand new installations (and in almost every local authority-run project) is testament to the widespread misunderstanding.

And whilst safe electrical installation is by no means beyond the scope of an intelligent DIY-er, I am in two minds as to whether forums such as this help or hinder that aim, when conflicting advice is merrily dealt out by some who are clearly deficient in that technical knowledge.
 
I'll do it as soon as I get my head around the 17th edition requirements for "effectively" bonded to the MET!
From what I can gather, if the disconnection times are met, all circuits in the location are RCD protected and the resistance is less than 1666 ohms between extraneous conductive part and the MET then it is considered effectively bonded.
Still not 100% sure on the last bit as I am thinking something outside the location can still cause potential to be introduced into the location via the extraneous conductive part.
If the resistance is 23k ohms or more then it isn't considered extraneous so doesn't require bonding anyway.
 
From what I can gather, if the disconnection times are met, all circuits in the location are RCD protected and the resistance is less than 1666 ohms between extraneous conductive part and the MET then it is considered effectively bonded.
Still not 100% sure on the last bit as I am thinking something outside the location can still cause potential to be introduced into the location via the extraneous conductive part.
If the resistance is 23k ohms or more then it isn't considered extraneous so doesn't require bonding anyway.

You're getting there.

First off, the 22K-ohms comes from GN5. A part exceeding this resistance, measured between the part and the MET is considered to NOT be an extraneous conductive part and therefore does not need supplementary bonding at all.

In practice you're likely to get either very much greater or very much less than this value.

There is no point in creating extraneous conductive parts by unnecesary bonding, so, if all circuits are 30mA RCD protected there is no need for any supplementary bonding at all. (The RCD will ensure that disconnection times are met and parts are either extraneous, but already bonded via MPBCs or not extraneous and need not be bonded.)

The 1666 Ohms is where you're getting mislead:

If not all three conditions can be met (e.g. not all circuits are RCD protected and you are modifying only one circuit) additional protection can be provided by supplementary bonding. Supp bonding can be carried out by a combination of CPCs, conductive parts or additional supp bonding conductors.

To decide whether you need to actually add extra green-an-yellers you measure the resistance (R) between accessible conductive parts in the location. If the measured value is less than 50V divided by Ia, then no additional bonding is necessary.

Ia is the largest value of the current causing automatic operation of the CPD of any of the circuits in the location.

For instance, if you have a 6A Type B CB on the lights and you have a 40A shower circuit, which is RCD protected, then Ia for the lighting circuit would be used and your R would have to be less than 50V/30A = 1.67 Ohms to avoid bonding.

It would only be in the case of all circuits being RCD protected that the value of R comes out at 1667 Ohms... in which case, you would not need to bond anyway, for te reasons already explained.

The only thing to worry about would be if you have extraneous conductive parts not bonded to the MET, such as metallic waste pipes going into a cast iron stack... but this should have been subjected to main bonding.


Anyway, after all that I have to say that it's all bolleaux - the only way you're actually in danger in a bathroom is if you're carrying out naked, wet, live electrical maintenance, in direct contavention of the requirements of the Electricity at Work Regulations 1989...

...and I tell you, fellas - never again! :D
 
Sounds like our Wiki needs revising. Could you do it?

For what it's worth I think that article is fine as it stands. It explains the basic principles very well without introducing the complexities of measurement.

In practice I genuinely believe the biggest risk in a bathroom has nothing to do with the reasons it is a special location, but rather with the likelihood of DIY/cowboy work being carried out with no awareness of possible dangers.

And the sort of person who does that does not frequent forums or ask advice anyway.
 
Cheers, I follow the logic in how it will protect from a fault within the location.
It is the part where the potential can be introduced into the location by a fault from outside the location which I don't like the idea of, say from a fault on an immersion heater not on an RCD in an adjacent room to the pipework.
We were taught that supplementary bonding was important as it also protects against a fault elsewhere in the premises.
 
Cheers, I follow the logic in how it will protect from a fault within the location.
It is the part where the potential can be introduced into the location by a fault from outside the location which I don't like the idea of, say from a fault on an immersion heater not on an RCD in an adjacent room to the pipework.
We were taught that supplementary bonding was important as it also protects against a fault elsewhere in the premises.

All bonding is done to limit the potential differences that may appear during a fault. It does this by keeping the resistance low between parts that may otherwise be at earth potential (extraneous) and parts that may become live during a fault; that is all exposed conductive parts of the installation.

Regardless of how that fault is produced, or where it originates the difference in potential in any location within the installation will depend on the resistances between those parts.

Have a look at the diagram on p.32 of the regs and work out how the protective measures applied in a bathroom will be effective regardless of where a fault appears in the installation.
 
Thanks for the advice.
I can get all the bits fitted now.

The onyl reason I asked about the bonding on the boiler was my current boiler has bonding between all of its pipes, which I assume was put in when the house was built (1993), however since then someone has been doing some soldering on the pipework and melted all the bonding :rolleyes:
 

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