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Discuss Supplementary Bonding Connections to CPCs in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

acvc

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Arms
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Sorry for this dumb question. How are you meant to get a 4mm supp bonding cable into the terminals of, for example, a light fitting/switched-fused boiler connection when their terminals can't physically accommodate it? Does the answer lie in something to do with getting the supp bonding down to 2.5mm by 'mechanically protecting' it (chased into the bathroom wall/conduit) and then it might fit into the relevant accessories? I do understand the theory of creating a Faraday Cage effect, keeping the touch voltage below 50V between extraneous/exposed. It's the practical side of it!

Thanks in advance.
 
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1

12345aob

I may of missed something here but why do you want to link supp bonding to switch's? what kind of installation are you doing?
 

acvc

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Arms
  • Thread Starter Thread Starter
  • #3
Thanks for your reply 1234. Not actually doing it, just wondering about a 'normal' small bathroom.

I've just been under the impression that you need to connect all extraneous parts together AND TO the cpc's of all circuits entering the bathroom if those circuits pass through or enter the zones 0, 1 and 2, so that exposed and extraneous parts in the zones have little or no potential difference between them under fault conditions.

So, the 4mm bonding (if unprotected) between the extraneous parts via the BS951 clamps, but how to connect to the circuit cpc's ...... confused ........ sorry. Connecting the 4mm to, for example, the shower or light cpc's, would be to include their exposed conductive parts in the equipotential zone. This is probably really dumb! Please put me right if I've got the wrong end of the stick here.

Thanks.
 
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ian.settle1

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Mentor
Arms
Thanks for your reply 1234. Not actually doing it, just wondering about a 'normal' small bathroom.

I've just been under the impression that you need to connect all extraneous parts together AND TO the cpc's of all circuits entering the bathroom if those circuits pass through or enter the zones 0, 1 and 2, so that exposed and extraneous parts in the zones have little or no potential difference between them under fault conditions.

So, the 4mm bonding (if unprotected) between the extraneous parts via the BS951 clamps, but how to connect to the circuit cpc's ...... confused ........ sorry. Connecting the 4mm to, for example, the shower or light cpc's, would be to include their exposed conductive parts in the equipotential zone. This is probably really dumb! Please put me right if I've got the wrong end of the stick here.

Thanks.
Thought under the 17th edition that it was not necessary any more unless disconnection times can not be made, aslo bathrooms should have a RCD fitted if wiring to the 17th.
 

acvc

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Arms
  • Thread Starter Thread Starter
  • #5
Thanks for reply Ian. Yeah, I am aware of the change with the 17th, RCD and disconnection times. Just wondering what I'd do if I came across a bathroom without RCD/satisfactory disconnection time/high Zs and supp bonding was required.

I know I am missing something stupidly simple here and expect to be flamed badly! How do I bond across say, a central heating pipe to an exposed conductive part of say, a light fitting? :confused::confused::confused:

Thankyou.
 

ian.settle1

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Mentor
Arms
Thanks for reply Ian. Yeah, I am aware of the change with the 17th, RCD and disconnection times. Just wondering what I'd do if I came across a bathroom without RCD/satisfactory disconnection time/high Zs and supp bonding was required.

I know I am missing something stupidly simple here and expect to be flamed badly! How do I bond across say, a central heating pipe to an exposed conductive part of say, a light fitting? :confused::confused::confused:

Thankyou.
Why would you have an exposed conductive part on a light fitting in a bathroom?
 

acvc

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Arms
  • Thread Starter Thread Starter
  • #7
"Why would you have an exposed conductive part on a light fitting in a bathroom?". Right, thanks Ian. You've been not very informative, a lot less entertaining. Anyone with a brain out there?
 
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W

WarrenG

acvc I have never personally bonded at the switch, more at the light fitting the switch is controlling i.e. the ceiling rose where the earth terminal is larger.

If the bonding is underfoor boards, or hidden in walls, then you will have your mechanical protection.

Hope this helps.

Warren
 
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tigerpaul

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Arms
I take the 4mm from under the basin and bath, and up inside the wall to the shaver socket and connect it in there. Usually the shaver, lighting and ext fan are all on the same circuit.

Now I didnt know that I would have to take another cable back up the wall to the shower as well. But surely the cpc's are bonded together back at the CU!

Another point, you cannot rely on rcbo's.. They fail after a while, and who is going to check them regularly like you are advised to?
 

jeremy

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Mentor
Arms
For non 17th bathrooms ( I know, I know!), all electrical circuits earthing has to be at the same potential. eg an electrical heater off circuit A woul have to be at the same potential as circuit B feeding the lights. To this end a connection ( if not mechanically protected ie only insulated) should be 4 mm csa from switch or luminaire to every other extraeneous metal part and then on to any other circuit eg fixed heaters (not very common these days) The idea is that all metal is joined together with all the other metal in the house. However if the bathroom is supplied by plastic pipe supp bonding between these pipes is not necessary
 
U

uksel

you are confused, i think you are intending to cross connect things to create an equipotential zone with supplementary earthing

this is not required, you supplementary bond between exposed pipework, that's it, it doesn't lead anywhere else, the water/gas pipes should have an earth connection at the consumer unit which connects all the earths to create the equipotential zone.

the faraday cage effect is another theory used in completely different applications, mainly industrial for large power surges to protect sensitive equipment.
 
U

uksel

my apologies, my post was a response to the initial post from ACVC

and in answer to you: extraneous conductive parts must be connected to your earthing system. supplementary bonding (before the 17th) was required to ensure the equipotential zone was maintained

and also ACVC, the keeping the potential voltage below 50V is called SELV and is used in bathroom circuits for low voltage lighting/shaver sockets etc.

the potential difference between extraneous conductive parts should be 0v, hence the term equipotential, which roughly translates as equal - potential.

i think theat between any extraneous conductive parts and exposed conductive parts you should have a resistance measurement of no greater than 0.05Ohms
 
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