Extraneous conductive part test

[tomodo]

Hi all, im aware of the test needed to be done when trying to find out if a metallic object is an extraneous conductive part but for example, if you had a copper water supply system in a house that is fed with a plastic incomer pipe out the ground you will always receive a low resistance reading due to multiple connections within the system ie at the boiler and water heating tank, is the only option to start physically disconnecting the boiler and all earth connections at boiler and immersion heater, control system to get a true reading? Even if you did and you had a high enough reading to determine that it did not require mains bonding, once connected back together the reading becomes low again so surely it would need to be bonded? What would an acceptable reading be to not have to add its own 10mm bonding cable?

 

[cliffed]

Hi all, im aware of the test needed to be done when trying to find out if a metallic object is an extraneous conductive part but for example, if you had a copper water supply system in a house that is fed with a plastic incomer pipe out the ground you will always receive a low resistance reading due to multiple connections within the system ie at the boiler and water heating tank, is the only option to start physically disconnecting the boiler and all earth connections at boiler and immersion heater, control system to get a true reading? Even if you did and you had a high enough reading to determine that it did not require mains bonding, once connected back together the reading becomes low again so surely it would need to be bonded? What would an acceptable reading be to not have to add its own 10mm bonding cable?

If it’s plastic it’s not an extraneous conductive part & needs no Main Protective Bonding Conductor.

 

[DefyG]

is the only option to start physically disconnecting the boiler and all earth connections at boiler and immersion heater, control system to get a true reading?

No if incoming service pipe is plastic a bonding isn't required within 600mm.
However!
Its always possible though that pipes to/from boilers , to radiators, hot and cold pipes within the system may go into the ground and if resistance is <23kohms then they may need bonding.

 

[HappyHippyDad]

Hi all, im aware of the test needed to be done when trying to find out if a metallic object is an extraneous conductive part but for example, if you had a copper water supply system in a house that is fed with a plastic incomer pipe out the ground you will always receive a low resistance reading due to multiple connections within the system ie at the boiler and water heating tank, is the only option to start physically disconnecting the boiler and all earth connections at boiler and immersion heater, control system to get a true reading? Even if you did and you had a high enough reading to determine that it did not require mains bonding, once connected back together the reading becomes low again so surely it would need to be bonded? What would an acceptable reading be to not have to add its own 10mm bonding cable?

If you can see a piece of plastic entering from the ground then (as cliff said), it does not need main bonding.
I think (not sure) this is reg 411.3.2
It says something along the lines of 'metallic pipes having an insulating section where they enter the house need not be connected to the main earth'.
Have a proper read though, as I haven't got the regs in front of me.