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Interlocked IEC 60309 sockets

Richard Henderson

I am looking at an existing design which we will be repeating a few times. It includes various sockets from 32A to 125A; all of them are interlocked IEC60309 type.

I cannot see a reason for them to be interlocked. What is the reason for an interlock anyway? I suppose it could be to stop people from poking their fingers into the female ‘pins’ of a live 125A socket but I'm pretty sure they're too small (standard IEC finger is 12mm). There is also the risk of them being disconnected under load and drawing an arc, but that seems a bit of a small risk to me unless in an EX zone, in which case, I'd imagine they're not allowed at all.

Does anyone know the  reason for the interlock and when it is needed? Particularly in the case of 125A?

 

thanks

  • 0

    It varies - sometimes it is in lieu of shutters - e.g. caravan sockets now have to be interlocked in some way (to prevent children poking things into live contact tubes) to give a similar level of safety to domestic sockets and for larger sizes (>32A) it's because the contacts aren't rated for functional switching of load currents (probably more due to the damage to the contact surfaces by repeated arcing events than any direct hazard from the arcing itself).

      - Andy.

  • 0

    Andy, thanks. Yes, that makes sense, particularly the caravan site point; I'm sure many children are inconsiderate enough to have fingers below standard dimensions.

    However, I'm hoping to find a definite statement from a standard etc that states when and where they should be used. My example is on a ship working in wind-farms. My feeling is that it has been specified simply by being overly-cautious.

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    Out of scope of BS7671.

  • 0

    It may be out of scope, but it is clearly not a household or similar environment, so 553.1.201 would not apply even if the workplace were on land.

    BS EN 60309-2 may have something to say about the requirement for sockets to be interlocked.

  • 0

    thanks. I don't think 60309 does and I don't have a copy, but I've just found that IEC60092 does call for it so that answers my question.

  • 0

    I'm hoping to find a definite statement from a standard etc that states when and where they should be used. 

    If it helps BS 7671 table 537.4 lists the suitability of various sockets for functional switching - from there it's more of a design decision on how to ensure that the larger sizes aren't plugged in or unplugged under load. If it's a controlled environment with trained personnel always following suitable procedures that it might all be sufficient - otherwise interlocking is a relatively easy way of ensuring that the plug/socket can't be abused.

       - Andy.

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