industrial bonding gas..?

[ColJack]

Just noticed at work yesterday that the main gas incommer ( big 6 inch pipe.. !!! ) is only "bonded" to the nearest board in 16mm² cable..

should this not be a bond back to the main earth for the installation which is about 50m away.. in the sub station ( we have our own transformer in there and the 11KV switchgear for the rest of the road.. along with the distribution chamber for or factory.. )

also, any idea what size it would have to be for that distance?

 

[GaryMo]

Not got BS7671 with me at the moment but you may need 25mm to keep resistance below 0.05ohms over 50M.
I think the maximum you can get with 10mm is 27M.
I'm sure somebody else will be able to check for certain.

Utilising structural steel is also an option under certain circumstances.

 

[Spark123]

Yeah, though in an industrial installation the fault currents can be a lot higher than in a domestic, a lot depends on the size of the supply, iirc the 0.05ohm is derived from a 50v touch figure for a 100A supply.

 

[ricicle]

If your incoming Neutral is 150mm² or bigger then the minimum size MEB should be 50mm²

 

[Spark123]

Ours are over 1" in diameter!! (suprised they are still there!!)