Supplementary Equipotential Bonding

[seftonbarn]

If you have accessible extraneous conductive parts within a room containing a bath shower etc then you need supplementary bonding unless a RCD is fitted protecting all circuits and the 3 conditions that go with the RCD are met.

Tony - Thanks for the reply. So this is irrespective of the fact that I cannot simultaneosly touch exposed conductive parts and extraneous conductive parts? Only 2 extraneous conductive parts?

 

[tony mc]

Looking at the post you must have access to the regs!

Have a look at sec 701 re loctions containing a bath shower etc re supplementary bonding!

 

[seftonbarn]

If you have accessible extraneous conductive parts within a room containing a bath shower etc then you need supplementary bonding unless a RCD is fitted protecting all circuits and the 3 conditions that go with the RCD are met.

Thanks Tony. So, to confirm. I need SEB even if I cannot simultaneously touch an exposed conductive part and an extraneous conductive part? In my situation I can only simultaneoulsy touch 2 extraneous condcutive parts.

 

[seftonbarn]

Looking at the post you must have access to the regs!

Have a look at sec 701 re loctions containing a bath shower etc re supplementary bonding!

Sorry about the duplicate thread. I have looked at 701. I just can't see the value in SEB if I can't touch exposed conductive parts.

 

[telectrix]

it's more if you can touch 2 extraneous conductive parts. if 1 were to become live, due to a fault, then as long as the 2 were bonded together, there would be no p.d. between them , therefore no shock.

 

[Top Cat]

it's more if you can touch 2 extraneous conductive parts. if 1 were to become live, due to a fault, then as long as the 2 were bonded together, there would be no p.d. between them , therefore no shock.

Oh Tel please don't tempt me over this!

 

[seftonbarn]

it's more if you can touch 2 extraneous conductive parts. if 1 were to become live, due to a fault, then as long as the 2 were bonded together, there would be no p.d. between them , therefore no shock.

OK. Bear with me. I am just tring to learn. So the lighting circuit in the bathroom is not relevant yeah? Because one of the the extraneous conductive parts could have become live due to a fault anywhere in the property? As I say bear with me.

 

[telectrix]

not quite sure of your meaning, TC. you been on the fish heads again?

 

[telectrix]

the point of bonding is to ensure that there;s no potential difference between extraneous conductive parts. imagine an earth fault ...... any bonded pipework will rise to 240V for the duration of the fault, till the MCB trips. as long as other pipework is bonded, it's potential will be the same. no PD = no current flow through you if you are in contact with both simultaneously.

 

[Guitarist]

If there is no RCD, then bond all pipework that enters the bathroom with 4mm cable. You can do this in an airing cupboard or loft, just so long as the pipework is continuous.

 

[ackbarthestar]

Come on chaps is relatively straight forward...

There are two conditions that exist in a location where you are naked and wet and hanging onto two metal bathroom components

1/ they are exposed
2/ they are extraneous

If they are exposed then they will be connected to the MET through the cpcs and 411.3.2.2 applies with 415.1
If they are extraneous then two further conditions are available:

1/ If they are connected to the MET via MPB and all metal pipework then 411.3.1.2 applies
2/ If they are isolated from the MET because of , either non metal pipework then GN5 and GN8 applies, that is

rx<= Uo/0.01 - 1k ohms which equates to 22k Ohms

So as long as simultaneously touchable metalwork is either bonded to MET or 'isolated' then you have some form of protection.

The confusion arises at what point does isolation stop and bonding begin.

Bonding to the MET infers that the touch voltage will not rise above 50V.

example: A lighting circuit protected by a 6A MCB has a maximum Zs of 7.67 Ohms which complies with table 41.3 but when compared with the requirements of 415.2 must not rise beyond 50V, so an alternative Zs tied down to the surrounding metalwork must be 50/Ia which would be 30A for a 6A MCB. This gives us a maximum Zs of 1.67 Ohms.

Now when used in conjunction with a 30mA RCD in compliance with 411.3.1.2, 415.2, 701.415.2

then Zs < Uo/IAN = 230/30mA

= 7.67 k ohms

This appears to comply with the disconnection time of < 40ms

However, even at 40ms (2cycles of ac) may still be sufficient to provide a kill

So to comply with touch voltage we have

Zs < 50/30mA = 1.67 k ohms

This satisfies both compliance for disconnection times 411.3.2.2 and compliance with 411.3.1.2

Now the problem arises when the resistance between simultaneously touchable parts sits somewhere between being bonded (> 1.67 kOhms) and Isolation (< 22k Ohms)

At this level both RCD and supplementary bonding needs to be present... cheaper just to supp. bond everything

Argue amongst yourselves

 

[seftonbarn]

OK. Bear with me. I am just tring to learn. So the lighting circuit in the bathroom is not relevant yeah? Because one of the the extraneous conductive parts could have become live due to a fault anywhere in the property? As I say bear with me.

OK. Interesting stuff. But what is the answers to my question/s?

 

[seftonbarn]

the point of bonding is to ensure that there;s no potential difference between extraneous conductive parts. imagine an earth fault ...... any bonded pipework will rise to 240V for the duration of the fault, till the MCB trips. as long as other pipework is bonded, it's potential will be the same. no PD = no current flow through you if you are in contact with both simultaneously.

Yes I agree. An earth fault can give rise to PD between extraneous conductive parts. What is confusing me is 415.2.2 which explains how you determine the effectiveness of Supp Bonding between Extran parts and the calculation is based on Ia which is the current of the overcurrent protection device or the RCD in the bathroom. What has the circuit in the bathroom got to do with it when the earth fault could have been introduced to the extraneous conductive parts from any number of other circuits in the installation. Hyperthetically lets say there was no circuits in the bathroom at all; just a metal bath and a radiator with metal pipework. Some of the explanations above suggest that you could still get PD between the extraneous conductive parts and so it would be logical to apply Supp bonding. But how does 415.2.2 work in this case when for the formula is R</50 V/Ia there is no value for Ia.

 

[Des 56]

If there is no potential difference between pipes that can be touched simultaneously,that is what is sought

All the regs and formulas only provide information to make a decision on what is necessary to obtain that situation

 

[seftonbarn]

Come on chaps is relatively straight forward...

There are two conditions that exist in a location where you are naked and wet and hanging onto two metal bathroom components

1/ they are exposed
2/ they are extraneous

If they are exposed then they will be connected to the MET through the cpcs and 411.3.2.2 applies with 415.1
If they are extraneous then two further conditions are available:

1/ If they are connected to the MET via MPB and all metal pipework then 411.3.1.2 applies
2/ If they are isolated from the MET because of , either non metal pipework then GN5 and GN8 applies, that is

rx<= Uo/0.01 - 1k ohms which equates to 22k Ohms

So as long as simultaneously touchable metalwork is either bonded to MET or 'isolated' then you have some form of protection.

The confusion arises at what point does isolation stop and bonding begin.

Bonding to the MET infers that the touch voltage will not rise above 50V.

example: A lighting circuit protected by a 6A MCB has a maximum Zs of 7.67 Ohms which complies with table 41.3 but when compared with the requirements of 415.2 must not rise beyond 50V, so an alternative Zs tied down to the surrounding metalwork must be 50/Ia which would be 30A for a 6A MCB. This gives us a maximum Zs of 1.67 Ohms.

Now when used in conjunction with a 30mA RCD in compliance with 411.3.1.2, 415.2, 701.415.2

then Zs < Uo/IAN = 230/30mA

= 7.67 k ohms

This appears to comply with the disconnection time of < 40ms

However, even at 40ms (2cycles of ac) may still be sufficient to provide a kill

So to comply with touch voltage we have

Zs < 50/30mA = 1.67 k ohms

This satisfies both compliance for disconnection times 411.3.2.2 and compliance with 411.3.1.2

Now the problem arises when the resistance between simultaneously touchable parts sits somewhere between being bonded (> 1.67 kOhms) and Isolation (< 22k Ohms)

At this level both RCD and supplementary bonding needs to be present... cheaper just to supp. bond everything

Argue amongst yourselves

Yes - so from the red text above I need to add supp bonding if my Zs is exceeding 1.67ohms (no RCD). But if I can't touch anything on the lighting circuit simultaneously with extran parts why use Ia of the lighting circuit. If the earth fault was introduced, lets say by an immersion heater protected by a 40A MCB and no RCD. Ia would then be 200A (from Fig 3A4) and so your calculation would be 50/200 = 0.25ohms. In other words shouldn't we be using the largest value of Ia in the installation rather than the largest value of Ia in the room containing the bath or shower.