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BS7671 switched protective conductors

Former Community Member
Former Community Member
While referencing BS7671 relating to standby generator earthing I came across the clause below:

537.1.5 Where an installation is supplied from more than one source of energy, one of which requires a means of earthing independent of the means of earthing of other sources and it is necessary to ensure that not more than one means of earthing is applied at any time, a switch may be inserted in the connection between the neutral point and the means of earthing, provided that the switch is a linked switch arranged to disconnect and connect the earthing conductor for the appropriate source, at substantially the same time as the related live conductors.


The requirement for the Earth switch pole to close at substantially the same time, should this be early make - late break to ensure this system is earthed prior to live conductors being closed?


Bill
Parents
  • 0
    My guess is that they have assumed that for standard commercial 3 or 5-pole rotary switches, the time difference between the different contacts connecting is negligible.  So it's unlikely that anybody would be electrocuted in the fraction of a second between the live connecting and the earth.


    If you wanted to guarantee that the earth connected before the live, you'd have to have a special switch made to do that.
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    My guess is that they have assumed that for standard commercial 3 or 5-pole rotary switches, the time difference between the different contacts connecting is negligible.  So it's unlikely that anybody would be electrocuted in the fraction of a second between the live connecting and the earth.


    If you wanted to guarantee that the earth connected before the live, you'd have to have a special switch made to do that.
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