Choosing best rating circuit breaker to protect 16A commando socket

I was installing a 16A commando socket today which I protected with a 30mA rcd followed by a 16A MCB.

Other breakers nearby were not heavily loaded so derating was not an issue. But if I say wanted to connect to a heavily loaded consumer unit my initial reaction would be to put in something like a 20A breaker and suitable cable.
But then I thought the socket and plugs are not fused and I have no control over the cable connected to the socket. Therefore do I have to assume I am protecting a cable that is only rated at 16A and never use a breaker with a rating that exceeds this?

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  • It also depends on the type of load - in general 16A sockets are not used in the same "plug and play" way as the 13A domestics, but there is some of the same uncertainty in some settings, like building sites and some kinds of workshops

    Certainly in "known load"  installations (I'm thinking of theatrical lighting and some types of outdoor events ) where the lamp load for one socket is very much planned and fixed as cables get installed, the rules are pushed a bit. Splitters that take a single 32A plug to  a couple of 16A sockets , with no fusing down, are quite common, though they are  a source of some teeth whistling and clucking noises from 'real' sparks. There is an assumption that the folk doing the set-up  are not random public, and are capable of adding up amps and not doing something too silly so both tails get a similar load and not one side dangerously over 16A..

    Mike.

  • It also depends on the type of load - in general 16A sockets are not used in the same "plug and play" way as the 13A domestics

    Problem with 13 A domestics is that BS1362 fuses tend not to be able to cope with starting currents of chunky machines in a well-equipped home workshop. One solution, which my friend did, is to machine a piece of brass rod to the appropriate dimensions. :-0

  • I suspect that a 13A plug without the fuse can withstand much higher currents without overheating.  The fuse is the biggest source of heat.

  • I cannot disagree. I don't think that I have ever felt a hot BS 1363 plug even connected to say, a 3 kW heater.

  • I cannot disagree. I don't think that I have ever felt a hot BS 1363 plug even connected to say, a 3 kW heater.
    1. What damages some socket-outlets? Occasionally, it's an overheating plug.
    2. I've seen plugs on some appliances where multi-way adaptors have been overloaded, or there are broken conductors in the flexible cable supplied by the plug.
  • I don't think that I have ever felt a hot BS 1363 plug

    I've come across a few. Seemingly a few EV owners with granny leads have too. I suspect in some cases at least it's a combination of events - heat from the fuse warms the socket contact springs,which means they gradually loose their temper, which results in a poor connection, with increased resistance, and so more heat. Probably not helped with the move away from pretty substantial thermosetting (urea formaldehyde?) plugs with solid brass pins to thermoplastic moulded ones with reduced c.s.a pins to allow for pin sleeving. Less mass to absorb the heat, probably less thermally conductive housing and lower surface area for heat to escape from, combined with a plastic that deforms more when warmed.

       - Andy.

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  • I don't think that I have ever felt a hot BS 1363 plug

    I've come across a few. Seemingly a few EV owners with granny leads have too. I suspect in some cases at least it's a combination of events - heat from the fuse warms the socket contact springs,which means they gradually loose their temper, which results in a poor connection, with increased resistance, and so more heat. Probably not helped with the move away from pretty substantial thermosetting (urea formaldehyde?) plugs with solid brass pins to thermoplastic moulded ones with reduced c.s.a pins to allow for pin sleeving. Less mass to absorb the heat, probably less thermally conductive housing and lower surface area for heat to escape from, combined with a plastic that deforms more when warmed.

       - Andy.

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