SNE and CNE

Thread Starter

Cerkit

Joined Jan 4, 2009
287
Why are guidance values for earth loop impedance so different for SNE and CNE earthing configurations?

CNE - 0.25Ohms

SNE - 0.8Ohms

Thanks
 

Dodgydave

Joined Jun 22, 2012
11,285
To provide a smaller earth resistance path, so a greater current will flow in the event of a fault, this will reduce the trip time of the circuit breaker, or earth leakage device.

Or as we say "the bigger the bang, the better the job".
 

Thread Starter

Cerkit

Joined Jan 4, 2009
287
I am assuming the resistance is quite different because the neutral conductor has a much smaller resistance due to it being much thicker than the outer sheath in an SNE cable?
 

Dodgydave

Joined Jun 22, 2012
11,285
Yes bigger cross section lowers the resistance, in a SNE, they use 3 conductors, in a CNE (PME in Europe) they use 2 conductors, the Neutral and Earth are one conductor, which is separated at the incoming fuse board by a copper bus bar.
 
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