Confusion over supplementary bonding

[hairyass]

hello guys, I'd just like you opinion as to whether I understand supplementary bonding.

To my mind supplementary bonding is additional protection to ensure that the voltage between extraneous and conductive parts does not exceed the safe voltage limit of 50. Therefore if you check between extraneous parts say a water pipe in a bathroom, and a conductive part, say a light switch, if the resistance does not exceed 230/30ma = 1667 ohms, and all circuits etc are protected by rcd, then no supplementary bonding is required. The formula is just used to check if supplementary bonding is required, if indeed the resistance is greater than 1667 ohms then it will be required, and as given in GN3 its resistance would have to be less than 0.05 ohm. The same argument applies to circuits that are not rcd protect, 50/Ia where Ia is the amount of current required to cause the mcb to function correctly, is this basically correct?

 

[malcolmsanford]

This is covered in section 701 of the regulations under regulation 701.415.2 and from there are references to several regulations in section 41.

 

[IQ Electrical]

Don't forget the use of the words 'simultaneously accessible' when looking at extraneous and exposed conductive parts.

In practice, it would often be far harder to isolate the metallic components in question from the protective bonding system.

 

[hairyass]

thanks for your reply, very much appreciated.

 

[Deleted member 26818]

Ensuring touch voltages are < 50V is a benchmark used to check the effectiveness of the bonding, it is not the primary purpose of the bonding.