Supplementary bonding in the Bathroom

[ap222]

Hello all,

I'm in the process of cross bonding all the copper pipes in my bathroom to the lighting circuit. I'm using 4mm cable and keeping the run continous between all pipes and hope to terminate at the light switch.

What I'm not clear on is that how do I connect the 4mm cable to the cpc of the lighting circuit, as the ground terminal at the switch is already overcrowded with earths from ceiling rose & extraction fan (2 gang switch).

Is it acceptable to run a short piece of 1.5mm sleeved earth cable from the light switch to an earth block that accepts 4mm cable from the earthed pipes?
Also, the extraction fan is earthed the same switch, so I believe this too will be cross bonded with the pipes, without a need to run a separate cable to the fan itself. Any help would be appreciated.
regards

 

[JohnD]

if you can get into the space above the ceiling, you may find it easier to connect at the ceiling rose.

apart from lighting, are there any other electrical circuits in the bathroom? immersion heater, CH pump, electric shower?

 

[LoveRocket]

Or you could "get with the programme" (as cool American teenagers would say) and ensure everything in the bathroom is RCD protected, and thus not need to bother with any supplementary bonding at all.

 

[ap222]

Thanks for the quick reply guys,
Yes, I can get to the ceiling rose. However the HWC/ immersion heater & CH pump are in an airing cupboard directly below the Bathroom, and all the pipes concerned run straight up into the Bathroom from there.

So I guess I could instead bond all the pipes (entering the bathroom)in the airing cupboard itself, and connect them up to the immersion heater switch. I can then run the earth cable from the bathroom lighting/fan circuit down into the airing cupboard. Will this be ok?
I know the bonding should be equipotential and within the vicinity of all the cpcs of all electrical circuits serving the bathroom.

As for RCD protection, im afraid I've still got the old wylex CU, and am looking to get it upgraded to RCD/MCB type.
regards

 

[dingbat]

I know the bonding should be equipotential and within the vicinity of all the cpcs of all electrical circuits serving the bathroom.

But do you know what that actually means?

I'd normally advise that you get an electrician in, but you won't find one that understands what's actually needed.

You almost certainly won't need most of the green-and-yellow cables you are attaching all over the place, but to decide what exactly needs doing you need a low-resistance ohmmeter and a calculation.

If the resistance between all simultaneously accessible exposed and extraneous conductive parts is less than 50 Volts divided by the Current required to disconnect the largest overcurrent protective device serving the location, then it is already effectively bonded. Assuming, from what you've written, that that is a 15 A BS 3036 fuse, that current is 90A and the calculation gives you 0.56 Ohms.

So, get out your meter and measure. If you measure more than 0.56 Ohms between, say the hot and cold pipes, or between pipes and a radiator, or between any pipework and the earthed part of any electrical equipment, run in a supplementary bonding conductor and measure again. Repeat until all measurements are below your 0.56 Ohms.

(Of course, if there is an electric shower in there you'll have to workout the maximum resistance based on the fuse for that item. And if you have plastic pipework there may be other numbers to consider.)

 

[ap222]

I know the bonding should be equipotential and within the vicinity of all the cpcs of all electrical circuits serving the bathroom.

But do you know what that actually means?

No I didn't but now I understand better from what you have just explained to me. Thanks.

It is a 15Amp fuse protecting the immersion hearter circuit. I'LL measure the resistance after each connection and aim for 0.56Ohms or under.
Thanks again you for the useful advice.

 

[holmslaw]

..

 

[dingbat]

This is the most irresponsible and downright dangerous nonsense since someone else on here suggested using a shorted out 13A plug as a method of proving dead at a socket outlet.

Except it is actually the correct method, as prescribed by the IET themselves and appears in the regs book, the commentary by Paul Cook, Guidance Note 5 and Guidance Note 8.

You have obviously assumed a persons body resistance to be zero to make your method acceptable.

No I haven't. But, in any case, the higher the body's resistance the better off you are.

So what now happens if a person gets connected between live and the bonded pipe? Oh dear what happened to the 0.56 ohm resistance? Why has'nt the fuse blown?

Supplementary bonding is not concerned with, but is in addition to disconnection of circuits. It is to reduce the difference in potential between parts that would otherwise be at very different potentials in the event of a fault.

You might want to check out Ohm's Law, but, if the difference in potential between the two parts is less than 50V, which is the point of the bonding, the potential difference across the body cannot be physically greater.

And in your scenario, if current is trying pass between two parts with 0.56 resistance between them, or via a parallel option through a body with a resistance of 500+ ohms, which path do you think the majority of current will take?

The ONLY way decisions on bonding can be made is by inspection of the various items. Resistance testing between the items is NOT an acceptable way of proving a common earth connection, because you have no idea how that connection has arisen.

Okay, calm down.

Inspection is one way - if there are visible connections everywhere an inspection may be sufficient. But most connections between extraneous and exposed conductive parts are made via the main bonding at the origin of the installation. Inspection alone cannot determine whether there is such a connection.

Are the pieces of pipe reliabley and permanently connected together?

You are absolutely correct in that the connection does need to be of a reliable nature, but isn't that part of the inspection process, in support of which your testing is really important, because, in order to verify that parts are actually extraneous you would and should...

...test back to the MET.

The figure you're looking for is not a maximum as you have advised. It is a minimum value and that value is 0.05 ohm or lower.

No, the generally agreed value between MET and suspect extraneous part is 22,000 Ohms - above that it can be considered not-extraneous.

Your 0.05 Ohms is actually the maximum agreed resistance of a single bonding conductor, whether main or supplementary.

As for this arrogant twaddle "I'd normally advise that you get an electrician in, but you won't find one that understands what's actually needed." you're the one who's understanding is lacking.

When you've gone back and re-read all those references, you can come back here and see where you went wrong.

Edited to add:

Or maybe you think Michael Faraday was wrong?

You haven't been reading David Cockburn's book have you?

 

[Spark123]

If the resistance between all simultaneously accessible exposed and extraneous conductive parts is less than 50 Volts divided by the Current required to disconnect the largest overcurrent protective device serving the location, then it is already effectively bonded. Assuming, from what you've written, that that is a 15 A BS 3036 fuse, that current is 90A and the calculation gives you 0.56 Ohms.

Correct me if I am wrong but if all circuits of the location are 30mA RCD protected then does the figure become a whopping 1666 ohms?
Not that I'd accept something that read anywhere near that.

 

[dingbat]

Correct me if I am wrong but if all circuits of the location are 30mA RCD protected then does the figure become a whopping 1666 ohms?

Yes, in theory, which is the principal rationale behind the 17th Edition relaxation of the requirement to bond.

Not that I'd accept something that read anywhere near that.

I can see why you'd say that, because you're imagining figures in that region. But you're unlikely to get values like that. You'll either get a few ohms or really massive values of resistance between conductive parts because those parts you thought were extraneous are, in fact isolated from the MET and would not require supplementary bonding anyway.

(Just because local authorities have always misread the requirement and grossly misapplied the practice of bonding does not mean they are right. Unfortunately, a great many electricians have been influenced by these poor practices, including the guy - ex-LA senior electrician - who taught the 2391 course I did quite some years ago. This same expert attended one of my regs courses in 2008 and he really revealed his true understanding of bonding - utterly clueless. He currently teaches apprentices; who knows what they will end up thinking?)

 

[dingbat]

I'm just curious as to whether holmslaw would like to respond.

 

[holmslaw]

..

 

[dingbat]

Oh, okay.

So you can't read and obviously don't understand the procedures, but as long as you are happy in your ignorant state, I guess that's that's all right?

Before you settle back into your intellectual torpor I really do urge you to read at least GN 8. I have no problems with differences of opinion - you are entitled to yours, as I am to mine - but I think that in matters of fact it is important to ascertain those facts.