upgrade or not

[Farmelectrics]

question a mate of mine who has a few houses, has just had an eicr carried out due to change of occupancy and the electrician has said the earth to gas and water wants up grading to 10mm . problem is the whole house as laminated flooring which posses a big problem for him he tells me . the earthing to water and gas looks to me 4mm but when i carried out an r2 test the reading i got was 0.04 end to end .so in theory does he really need to lift the flooring.

 

[telectrix]

just to clarify... the 0.05 ohms is the max. you should get from the bonding cable end to the pipe that it's bonded to. nothing to do with the resistance of the bonding conductor.

 

[DPG]

Yep, sorry folks. I could have sworn I'd seen it somewhere recently that this was also a guideline for the bonding conductor itself. Point noted. Daz

 

[Farmelectrics]

ok must admit myself thought the 0.05 value was for the bonding conductor so theres no set value or measured value for a bonding conductor 6mm min and obvisoly 10mm for new installs or up grades i have allways upgraded to 10mm myself but could understand the customer not wanting the laminating flooring lifted and surface is an eye sore in my eyes

 

[stevethesparks]

I have seen this argument appear many times, there is a table somewhere (buggered if I can find it at the moment) that gives recommended maximum lengths on copper bonding conductors i.e 10mm - 27 mts, 16mm - 43 mts, 25mm - 68 mts, all of which approximately equate to 0.05 ohms.

Also many other threads have shown this argument. I would like to see it cleared up once and for all.

http://www.electriciansforums.co.uk...ations/15605-maximum-length-main-bonding.html

http://www.electriciansforums.co.uk.../67623-0-05-max-impedance-main-bonding-2.html

 

[Farmelectrics]

well thats what i thought as well steve many year back i was testing on a new build commercial building and one of the tests was making sure i had a reading of 0,05 on all main bonding cables ie water gas steel structure etc and the longer the run the bigger the csa of cable to maintain that 0.05 reading

 

[Richard Burns]

All references to a 0.05Ω resistance are recommendations or guidance to the tester and are in no way a requirement.

As far as I am aware (though I have not read all the AMD3 updates) only GN3 mentions 0.05Ω.
In regard to periodic inspection and testing for an EICR:
GN3 mentions that if you cannot see or access supplementary bonding conductor connections in a location then you can assume they are present if the continuity between exposed/exposed, exposed/extraneous, extraneous/extraneous conductive parts is <0.05Ω.
GN3 also mentions that if you are testing the main protective bonding conductors the expected value is likely to be in the region of 0.05Ω.

This has no relevance to initial installation or any design parameters, it is a guide to expected levels of resistance to be be found during an EICR.

Resistance of bonding conductors is of little relevance whilst they are performing their usual function as the current flow in the bonding conductors during a fault should be minimal and so when considering touch voltages the volt drop will also be minimal (Volt drop = Vd * A * m; A is very small so volt drop is very small).

It is important to ensure that bonding conductors are firmly connected and so they should demonstrate a low resistance when continuity is measured.

Bonding conductors may also carry the installation neutral current if the neutral is disconnected to a TNCS installation and the only path for current to travel is via extraneous conductive parts to earth so they should be able to take this current.

Obviously the minimum cross sectional area is limited by the requirements of the regulations but this is irrelevant to this discussion.

 

[DPG]

Great post Richard. Daz