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machine safety guard switches

Discussion in 'Electrical Engineering' started by bob watkinson, Dec 3, 2004.

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  1. Anyone know if the UK has a specific regulation that states the frequency
    that safety guard switches should be tested.

    Thanks
     
  2. Sileby Pie

    Sileby Pie Guest

    Hi Bob,

    As far as I know there is no standard that covers this. Even EN 1088
    gives no guidance. It comes down to your risk assessment and the
    potential loss of the safety function ( and risk reduction loss) if the
    switch, or its circuit has a fault.

    You must consider what faults could occur and how they could be detected.
    Single and dual channel circuits behave differently under certain single
    faults, but the problems become more dangerous if there is a build up of
    faults or the monitoring of the circuit cannot detect all faults.

    The one thing that I come across regularly is that people never check
    each switch individually ( if they check them at all!). Even if you have
    a dual channel redundant circuit going back to a safety relay, you can
    only check the correct operation of the first switch that you open and
    the last that you close. Wiring a number of switches in series can hide
    faults.
    Even daily testing of swicthes done wrongly could prove nothing, so
    consider the process for testing as much as the frequency.
    Apologies if I'm teaching you to suck eggs.

    Jim
     
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