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testing safe of a 16 Amp commando socket/plug

Former Community Member
Former Community Member
Hello,i am an RF engineer and we have equipment that is fed by rack mounted AC/DC converters which charge batteries. these converters are wired into fused spurs using 2.5mm arctic blue cable routed into cable trunking. the 2.5mm cable is fixed in the rack before entering the trunking.

At the moment we are all trained in testing the circuit is switched off using a martindale VIPD138 voltage indicator and proving unit and then we lock off the circuit.

Everyone's training is due to expire and our company health and safety department want to change the installation from the fused spur to 16 Amp commando sockets/plugs rather than retrain everyone in proving the circuit has been switched off.


I have no issues with using commando sockets instead of the fused spurs but my concern is that if the nearest location the commando socket can be mounted is the other end of the room and there are numerous commando sockets supplying different racks how do you prove you have pulled the correct plug? surely you have to still be able to test the circuit has been switched off using the tester and training required.


I am having a discussion with the Health and safety department next week so any advice would be gratefully received.

Thanks
  • 0
    if the light is on, it's alive.

    But bare in mind that the converse isn't necessarily true - if the light is off it's not necessarily dead - it could be live but with a failed lamp - a small chance perhaps but not what you'd want to bet you life on. If you were to rely on an indicator lamp you'd perhaps need to adopt a procedure similar to testing for dead - i.e. check it's on first, then pull one plug then check it's off (and perhaps put the plug back in and check it lights again to prove that it didn't just happen to fail while you were tugging various flexes about trying to pull the plug out, before pulling the same plug finally out) - which isn't really much less onerous than using a voltage indicator.


       - Andy.
  • 0
    mapj1:

    We need the OP to come back and clarify - I had read it that there were exposed parts, as part of whatever the process is, and the question is more is unplugging and visual verification better than a switch.

    If not a pilot light would be a better design


    My understanding was that the supply is isolated and locked off. Then a lid is removed and before any further work is undertaken, the supply is proved dead.


    The alternative which has been proposed is to isolate by removing the plug so that proving dead is unnecessary. IMHO, that is fine provided that the plug remains under the control of the technician in the same way as the key of the padlock would be.


  • 0
    Sparkingchip:

    To use a Martindale VIPD138 voltage indicator and proving unit to carry out safe isolation you have to open the terminal enclosure and test at the live terminals, which unless the equipment is being repaired and the enclosure needs to be opened for work to be carried out is not appropriate, is it?


    There is always a risk that in the course of proving dead, the supply is in fact found to be live. If that were not the case, proving dead would be pointless, would it not?


  • 0
    I find this question curious. RF equipment is usually inside boxes, and this suggests it all comes from external power supplies. Possible, because I think there is more to this than meets the eye. I suggest this is a phone network base station or similar, where the voltages will not be great from the power supplies, Perhaps 50V DC maximum. If it is changing a power supply, how does the mains connect to it, with a connector or a terminal block? Dead testing is in one case unnecessary and the other fairly simple. Probably box-ticking, perhaps by someone who doesn't fully appreciate the job. None of this equipment would be repaired in situ, except perhaps changing a fuse.
  • 0
    Proving dead often starts with proving it’s live.
  • 0
    Sparkingchip:

    Proving dead often starts with proving it’s live.


    So you do want to take the lid off before isolating? Make your mind up!


  • 0
    Prove the tester.

    Prove dead.

    Prove the tester.


    Consider the safe isolation procedure for a domestic consumer unit. The cover is off and you are proving dead, the main switch input terminals remain live whilst you work within the consumer unit.


    So you prove the tester using the input terminals of the main switch, then prove the output terminals are dead, then prove the tester again on the input terminals.


    You don’t need a proving unit for a domestic consumer unit that always have live terminals within them that you can use to prove your tester.


  • 0
    If you look at the NICEIC guide you will realise that the incoming terminals of the locked switch remain live, so yes you do work in enclosures with live parts.

    https://dms.niceic.com/0000002378.pdf
  • 0
    In many instancs it would be impossible to legally work inside a consumer unit witout live incomming terminals.

    Of course these days the seal fairy has a bigger army of supporters than in days of yore.



    If you work on a single item that has a simple plug and socket arrangement then good enough. But multiples is a disaster waiting to happen unless extremely robust procedures operate. Remove the plug and put it in your pocket ?
  • 0
    Maybe I am just getting old, but I cannot remember there being voltage tester proving units in the college workshop, we were taught to test the tester on a known live supply then disconnect and prove dead, it was then proving the tester was still working that became difficult if the enclosure did not have live terminals in it.


    We were working in pairs testing consumer units in the college workshop and I was pushing the cover back on, the lecturer asked why saying we still had some more testing to do in a few minutes, I nodded at the guy who was supposed to be working with me but wasn’t paying attention and was talking to a guy in the next booth and said I didn’t want him to get an electric shock. The lecturer smiled and said it probably was a good move.


    When the meter guys and DNO guys pull the main fuse there al live terminal in the fuse holder that is not shrouded, Just one of the dangers from pulling the main fuse.


    Even disconnecting a washing machine from the supply by unplugging it doesn’t make it electrically safe does it?


    Consumer units have live terminals when “isolated”.


    Owning and using a proving unit doesn’t mean the unwary  are safe.

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