Whilst we're on the subject of bonding...

[HappyHippyDad]

We all know that if something is extraneous then it needs to be bonded. However, if we have some water pipes in a bathroom for example that test at 0.2Ω to earth (MET) would you be happy with that? Let's assume it has RCD protection. I realise some say that if the extraneous tests at <1667Ω then the RCD will trip before the potential rises to 50V, however I don't feel very comfortable with this as the RCD is for 'additional' protection.

GN3 states that if the resistance to earth of the extraneous is <0.05Ω then we can assume the extraneous is bonded. So, my question is 'would you feel it necessary to take a separate bond to the pipes in question in the above example as they are > 0.05Ω? If you are happy with this then what resistance would you feel is a maximum before you feel the extraneous needs bonding?

With Zs figures there are very clear limits. The only limit I can see in these sort of examples is 0.05Ω.

 

[telectrix]

the 0.05 value is between a bonding conductor and the pipe it's connected to. you'd expect a higher value from MET to other pipework due to resistance of bonding conductor and copper pipe.

 

[Pete999]

the 0.05 value is between a bonding conductor and the pipe it's connected to. you'd expect a higher value from MET to other pipework due to resistance of bonding conductor and copper pipe.

Hi Tel I'm a bit confused with your answer, not saying your wrong, wouldn't dare, but is the 0.05 ohm limit the reading from the end of the bonding conductor and the pipe near to where the bonding clip is? seem to recall Chris Kirchers description on his video says just that.https://www.youtube.com/watch?v=rnvNfI__kYU

 

[Hellmooth]

I think that's what Tel was saying?

 

[telectrix]

always confusion with this. all i can say is can ayone post the reg. ( in BS7671, not additional publications, which are , by definition, guides). that quotes this 0.05 value for a resistance from MET to a water or gas bond.

 

[Risteard]

As tel says the Guidance Note is merely pointing out that such a negligible reading suggests that the connection e.g. BS951 clamp is making an effective connection to the extraneous conductive part. There is no maximum reading for the bonding conductor, nor is the guidance (which does not nor has it ever) form part of the Wiring Regulations.

 

[Pete999]

I think that's what Tel was saying?

I took it as Tel was saying from the clip to the pipe, at least that's how it came over to me, if I got it wrong then the eggs on my face

 

[Deleted member 9648]

In a bathroom supplementary bonding is not required as long as disconnection times are met....all circuits within the bathroom are RCD protected, and extraneous conductive parts within the location are effectively connected to the main bonding. For the purpose of effectively connected to main bonding a continuity reading of <1667 ohms is considered satisfactory.
If these conditions are not met then supplementary bonding is required.
In a domestic supplementary bonding is only likely to be required in bath and shower rooms. Nowhere else.

Good enough for me.

 

[telectrix]

also, if the piework to MET reads > 22k on IR test, it can be assumed to be non-extraneous. just thought i'd chuck that in.

 

[HappyHippyDad]

In a bathroom supplementary bonding is not required as long as disconnection times are met....all circuits within the bathroom are RCD protected, and extraneous conductive parts within the location are effectively connected to the main bonding. For the purpose of effectively connected to main bonding a continuity reading of <1667 ohms is considered satisfactory.
If these conditions are not met then supplementary bonding is required.
In a domestic supplementary bonding is only likely to be required in bath and shower rooms. Nowhere else.

Good enough for me.

This is what is written and used by many I believe. I can't quite see how we use a figure of 200Ω for a TT, yet we are happy to use the 1667Ω in this case. They are both designed to make sure the RCD operates so that the potential is <50V but with a figure of 1667Ω there is little room for error, in fact none! Is this 1667Ω stable? At such a high value its doubtful that it has any thoughout or rather intended route to the MET so perhaps this resistance is purely due to its location to the general mass of earth... In which case its not stable.

I'd value your thoughts on this Wirepuller and also if you would be happy if you actually did come across a value of 1667Ω between the extraneous and the MET? (Am assuming RCD present)

 

[Deleted member 9648]

To be honest I've not been overly concerned with supplementary bonding in bathrooms since the introduction of RCD protection to all circuits within the location. Main bonding is far more important as far as I'm concerned. Most people just assume if RCD protection is up to scratch then SB can be ignored. Not the case and I do measure continuity, more often than not if continuity readings are >1667 ohms then it can be established that pipework is not extraneous anyway. Just because there is a copper pipe in a bathroom does not mean it is extraneous, often wetpants use plastic under floors and just rise up into the bathroom in copper.
Complying with the regulations is as far as I see the need to go.

 

[Midwest]

This is what is written and used by many I believe. I can't quite see how we use a figure of 200Ω for a TT, yet we are happy to use the 1667Ω in this case. They are both designed to make sure the RCD operates so that the potential is <50V but with a figure of 1667Ω there is little room for error, in fact none! Is this 1667Ω stable? At such a high value its doubtful that it has any thoughout or rather intended route to the MET so perhaps this resistance is purely due to its location to the general mass of earth... In which case its not stable.

This other vid from Chris Kitcher; https://www.youtube.com/watch?v=v38PfIVy2rI talks about the reasoning for those values. Its mentioned at 2.35. Dunno, if that answers your question?

 

[sam400]

I have to be honest I don't really understand where 415.2.2 is coming from,
I thought the purpose of supplementary bonding was to keep touch voltages to a minimum, having a resistance of 1667 between an extraneous conductive part and exposed conductive during single fault conditions will surely give rise to a touch voltage approaching the supply voltage?
can someone enlighten me?

thanks

sam

 

[Richard Burns]

If you have an RCD in place then the fault current only needs to be 30mA before disconnection takes place, at this current the 1667Ω resistance will only generate a 50V touch voltage which is the deemed safe level.

V= I * R = 0.03A * 1666.6666Ω = 50V

 

[i=p/u]

main bonding/supplementary is useless nowadays as all piped in plastic and rcds on scene.....