415.2.2

[fattony]

Just got my new 17th edition and been doing some bed time reading, sad I know, Regulation 415.2.2 states:

Where doubt exists regarding the effectiveness of supplementary equipotentional bonding, it shall be confirmed that the resistance (R) between simultaneously accessible exposed conductive parts and extraneous conductiv parts fulfils the following condition

R<50V/Ia

Does that basically mean if the resistance between the exposed and extraneous conductive parts is that of the above formula supplementary bonding is not required, as R is less then or equal to the touch voltage 50v

 

[SeanT]

Why didn't they just write IaR<50V - the same equation multiplied through by Ia on both sides to make it more logical - ie. the voltage likely to develop (calculated by Ia * R) is less than 50V - what current is Ia again? The fault current?

 

[GaryMo]

Ia:

For RCD's I delta n
For overcurrent devices, the current causing automatic disconnection in 5s

 

[SeanT]

"Fault" (trip) current in laymans terms / my little brain then

So it's just a simple resistance check (along with proper establishment of the value of Ia) to confirm that the supplementary bonding is adequate, provided it's there in the first place and said low resistance isn't just coming from the pipes being in contact or something equally silly.