Main Equipotential Bonding

[trebor]

Is there a maximum resistance value for main bonding ?

Having read 2 books by so called experts, one says there is no value as it depends on the length (logical) another says a max of 0.05 ohms, I can see in GN3 this figure for supplemetary bonding between 2 accessible extraneous parts but nothing for main bonding, any help please

 

[acat]

Ideally you are looking at the 0.05 ohms so for example if you were using 10mm the max length would be 27 meters to achieve the 0.05 reading.

Hope that helps


Chris

 

[Guest123]

To check the effectiveness and compliance of supplementary bonding, the total resistance (R) between exposed and extraneous conductive parts must not exceed the calculation of 50V/the mA rating of the associated RCD.

I.e, 50/0.03 = 1667ohms.

Where there is no RCD protection then the current causing the fuse/MCB to disconnect in 5s is used instead of the RCD rating.


Bathrooms would be one example whereby supp bonding may now be ommited if ALL circuits within that bathroom are protected by a 30mA RCD.

As for MEB, Chris is correct.