Main bonding of plastic/copper services

[dtec dave]

Morning all...

I am working on a property which has just had a lead water mains replaced with plastic. This comes from the main stop tap outside, then passes through the cellar for 8 meters, this then converts into copper which feeds the house.

I am unsure as to whether this needs main bonding, the onsite guide states that it doesn't if "it has been confirmed that any metallic pipework within the building is not introducing earth potential" (section 4.5)

How is it possible to confirm this? Is this done by supplementary bonding?

Thanks in advance

 

[telectrix]

loads of previous threads on this. IR test between the suspect copper pipe and the MET. if the reading is above 22K ohms then the pipework is not exreaneous, and you don't need to bond it.

 

[dtec dave]

Is the 22k reading anywhere in the regs??

 

[Richard Burns]

Is the 22k reading anywhere in the regs??

It is not in the regs it is a calculation based on the human body's resistance.

MarkieParkie in this post states (very succinctly):
To determine if a part is extraneous, or just a piece of metal, test with an Insulation Resistance Tester on the MOhm range at 500Vdc between the suspect metal part and the MET, if the reading is 0.022M Ohms (22K Ohms *) or greater supplementary bonding is not required.
* Conservative traditional value used by most electricians, however GN8 advises 23K Ohms and ESC/NICEIC advise the ultra-conservative 7K Ohms.

 

[Guest123]

This is the NIC take on it.......


Ripped form an NIC newsletter.....

The NICEIC are now quoting a figure of 7000ohm (based on 30mA fault current for a disconnection time of 0.4s). It was dicussed in a recent connections magazine and also discussed at one of their tech talks.

From pg 47 in the magazine issue 172
The metallic part can be assumed not to be an extraneous-conductive-part if the following condition is met:
Rcp> (Uo/Ib) - Ztl
where,
Rcp is the resistance between the conductive part and the MET in ohms
Uo is the nominal voltage to Earth in volts
Ib is the value of current through the body in amperes that should not be exceeded. (The value may be taken as 30 mA for a disconnection time of up to 0.4 s, as given in DD IEC/TS 60479)
Ztl is the impedance of the human body in ohms. The value suggested in DD IEC/TS 60479 is 1000 ohms where Uo is 230 V (50 Hz) under dry or wet conditions.
Taking Ib as 30 mA and Ztl as 1000 ohms (as suggested above where the disconnection times in the installation are 0.4 s or less and Uo is 230 V), the limiting value of Rcp is given by:

Rcp > (230/0.03) - 1000
Rcp > 6667ohms

Thus, if Rcp exceeds 6, 667 ohms, the pipe may be considered not to be an extraneous-conductive-part, such that main bonding of the pipe is not required ​