SNE and CNE

Discussion in 'The Projects Forum' started by Cerkit, Feb 23, 2015.

  1. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
    275
    3
    Why are guidance values for earth loop impedance so different for SNE and CNE earthing configurations?

    CNE - 0.25Ohms

    SNE - 0.8Ohms

    Thanks
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    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".
     
  3. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
    275
    3
    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?
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    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.
     
Loading...