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Hi all, have a question about an earth marshaling point. Just looked at a building where there is no bonding present at the incoming water stop cock (although a bond has been made somewhere, from a sub CU).

If i put a clamp on the incoming water is it acceptable to run a cable to earth bar of a sub CU, so long as total resistance back to the MET (via the sub cable) is within 0.05 ohms ?

If I can do this is the CU's earth bar classed as a mashalling point ?, or does a marshalling point have to be an actual earth block ?

Thanks
 
that 0.05 ohms is not relevant. it applies to the resistance between a bonging cable and the pipe it's attached to. i.e. the resistance of the clamp.
 
it' swhat i've always understood. say you have a 10mm bonding cable. then @ 25m you have reached 0.05ohms. any longer you's be over that.
 
it' swhat i've always understood. say you have a 10mm bonding cable. then @ 25m you have reached 0.05ohms. any longer you's be over that.

And if its under 0.05 then its suitable, theres a lot of posts about this. Anyhow can an emp be the earth bar of a (sub) cu, or does it have to be a earth block in iteself, although I cant see what difference it would make apart from accesability.
 
Don't see why not as long as the supply cpc to the CU can support bonding. So if your bond is to be 10.0 then cpc to CU should be 10.0 or above.
 
If you run a bonding conductor from the extraneous service to a CU and use the CU earth bar as a junction point and then there is a suitably sized conductor from that CU going to the MET then this is fine.
I suppose you could call it an earth marshalling point but it is just a joint in a conductor.
 
Hi all, have a question about an earth marshaling point. Just looked at a building where there is no bonding present at the incoming water stop cock (although a bond has been made somewhere, from a sub CU).

If i put a clamp on the incoming water is it acceptable to run a cable to earth bar of a sub CU, so long as total resistance back to the MET (via the sub cable) is within 0.05 ohms ?

If I can do this is the CU's earth bar classed as a mashalling point ?, or does a marshalling point have to be an actual earth block ?

Thanks
If, and only if, there is an adequate cross-sectional area on the protective conductor supplying the distribution board then it could be used as a combined cpc and bonding conductor. Then you could connect your main protective bonding conductor to what would be an Earth Marshalling Terminal (as the installation only has one MET, so this is an EMT).

0.05 Ohms is just to demonstrate a negligible impedance between the connection of the main protective bonding conductor to the extraneous conductive part (e.g. pipe) being bonded. So you could measure between the connection of the main protective bonding conductor on the BS951 clamp to the pipework itself. There is no restriction on the measured resistance of the main protective bonding conductor. (This can be verified by the fact that there is no Regulation which states that there is.)
 

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