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OT: (electrical question but related to a machine)

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  • #16
    What UL generally requires for a "control circuit" in equipment I do controls for is that clearances to all other circuits be equal to that for the highest voltage in the box. Insulation ditto.

    that isn't universal, so refer to the specific standard if you need to know.

    The effect of that requirement is to make inadvertant shorts very unlikely. it is recognized that nothing is perfect. The standards don't require perfection, they require reasonable construction to prevent problems.

    It is nearly always possible to envision a series of failures which collectively create a hazard, all you do is assume that every precaution is nullified.... That brings you back to where you started.

    The assumption is, right or wrong (and in many shops, its wrong) that once a failure of one type becomes known, it will be fixed before it can combine with future failures to cause a hazard.

    Most standards are "one failure", some assume two. Knowing what goes on, two may be better, but the fact is that it only takes one more than you plan for, no matter what. And the better-protected, ironically the worse the safety may be.... if it allows one failure to be ignored, or worse yet, unknown.
    1601

    Keep eye on ball.
    Hashim Khan

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    • #17
      Originally posted by J Tiers
      What UL generally requires for a "control circuit" in equipment I do controls for is that clearances to all other circuits be equal to that for the highest voltage in the box. Insulation ditto.

      that isn't universal, so refer to the specific standard if you need to know.

      The effect of that requirement is to make inadvertant shorts very unlikely. it is recognized that nothing is perfect. The standards don't require perfection, they require reasonable construction to prevent problems.

      It is nearly always possible to envision a series of failures which collectively create a hazard, all you do is assume that every precaution is nullified.... That brings you back to where you started.

      The assumption is, right or wrong (and in many shops, its wrong) that once a failure of one type becomes known, it will be fixed before it can combine with future failures to cause a hazard.

      Most standards are "one failure", some assume two. Knowing what goes on, two may be better, but the fact is that it only takes one more than you plan for, no matter what. And the better-protected, ironically the worse the safety may be.... if it allows one failure to be ignored, or worse yet, unknown.

      You will get an award from the plain English society for that post Jerry.

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