Agreed. However, yesterday you said if over 0.05 it would require bonding in all cases regardless of RCD (plus ADS and main bonding) being in place.
What I was trying to say was that if the connection between the point where the extraneous conductive part is bonded and the MET was higher than 0.05Ω then it wasn't an effective main bonding connection. I was aware of what I was trying to say although I must admit I was struggling to find a way of putting it down and probably didn't explain myself as well as I could have done. I haven't read back through what I said but I apologise for any confusion.
This is where we differ.
The figure of 0.05Ω is a value regarded as negligible impedance when testing, it is not a value which determines whether supplementary bonding is required.
Negligible impedance is unlikely to be achieved by cpcs.
As you have already established the effective connection to the MET (above) then if R≤50/Ia is not achieved between the e-c-p-s supplementary bonding will be required.
Obviously R≤50/Ia between parts and the MET can add up to more than that between the two parts. This why supplementary bonding is required to be added.
Yes, it would appear as though we do differ on our opinion as to what the 0.05Ω value means. I am aware it is only a suggested value but GN3 clearly states that: 'When testing the effectiveness of main bonding conductors, the resistive value between a service pipe or other extraneous-conductive -part and the MET should be of the order of 0.05 ohms or less'. I read it as it is.
My argument is that although on the face of it, even if the resistance between the point of testing within the bathroom on exposed pipework or structural metalwork and the MET is less than or equal to 50V/Ia, if the actual main bonding conductor is higher than 0.05Ω then it could be argued that the main bonding conductor is not effectively connected, so regardless of R≤50V/Ia, one of the three conditions is not met. I concede however that this point is arguable and open to interpretation.
No, maximum Zs allows more than R≤50/Ia - so the disconnection times will be satisfactory.
Also - 0.05Ω is not possible unless very short. 3m for 1mm - 11m for 4mm.
I have never stated (or at least never meant to give the impression) that the value of 0.05Ω applies between CPCs or exposed conductive parts and the MET. What I was trying to say is that R≤50V/Ia does apply
between exposed conductive parts as much as it applies between extraneous conductive parts. The maximum Zs for a circuit is defined by Uo/Ia but the whole point of supplementary bonding is to prevent a rise in potential between simultaneously accessible exposed and/or extraneous conductive parts of more than 50V therefore the figures used to define maximum Zs values cannot be used.
Agreed, but not what you said yesterday.
I may not have done but I'm pretty sure I didn't say anything to the contrary. The point I was trying to argue if I remember rightly was the meaning of 'an effective connection to earth', not a result measured to bolster an assumption. If I did give the impression that this was not the case somehow then I apologise as I certainly didn't mean to.
Well, not really. This seems like you are making up hypothetical situations.
Radiators (unless fixed to the ground) cannot be extraneous. The pipes feeding them may be but obviously not if plastic.
No, I'm not. The situation I gave where the radiator measured 6kohms to the MET was entirely real! You seem to have disregarded the fact that although a pipe can be plastic and non conductive, the water flowing through it is conductive. Therefore, it is entirely possible for something not fixed to the ground and fed in plastic (in part or in whole) to be extraneous! This is what makes lazy plumbers and their penchant for PVC tees such a blimmin minefield when it comes to supplementary bonding! The simple solution I use when plumbing using PVC between copper for anything is to supplementary bond over any PVC joints to keep copper continuity. In a property where the water service is extraneous, this
needs to be done!
Ah. This may be a source of confusion yesterday but whenever mentioning omission of supplementary bonding because of RCDs I have always included the other two requirements.
So, agreed, but with the proviso that a plastic fed radiator cannot be extraneous (unless fixed to the ground).
As I've already said, a plastic fed radiator
can be extraneous even if not fixed to the ground.
Agreed, plus - an effectively connected extraneous conductive part may also still require bonding.
Again, my argument is that if an extraneous conductive part still needs bonding then it is not effectively connected in the first place.
No, it is just the continued use of 0.05Ω (which is not mentioned in black and white in BS7671 and mentioned in GN3 only as an acceptable value for negligible impedance only) as a limit or level in regard to supplementary bonding.
It has nothing to do with supplementary bonding (or main bonding) other than to establish a good connection between the bond and the bonded part.
Again, GN3 states that: 'When testing the effectiveness of main bonding conductors, the resistive value between a service pipe or other extraneous-conductive -part and the MET should be of the order of 0.05 ohms or less'. This is clear to me and does
not mean that the resistance of the actual bonding clamp has to be lower than 0.05Ω.
R≤50/Ia is the only value to determine an effective connection between extraneous parts to the MET and between parts for supplementary bonding - but not cpcs because of maximum Zs.
I say that this is still arguable as I don't see how an inneffective bond can still be an effective connection. Also, R≤50V/Ia
does apply between exposed conductive parts as well as extraneous conductive parts.
