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32a Commando Socket with UMC

Just in case you are not playing silly buggers and for those that might think that that cable is a good idea.

The 32a breaker for the commando (assume its 32a as thats what the commando socket is) will not protect the extension cables 2.5mm cable that will be rated at 20 or so amps.

You have a double socket with a total capacity that potentially can exceed the rating of the cable. Whilst a single device may be max 13a fused, 2 devices would potentially exceed the rating of the cable and the individual fuses are rated each too low to be protecting the cable.

With a normal extension cable, its fused in the plug of the extension cable, or sometimes additionally in the extension cable socket. This is what is protecting the extension cable. But in the case of the commando setup, there is no fuse, nor one in your double socket, so the only fuse in play here with the potential to protect the cable is the main circuit breaker, but that's probably rated at 32a so won't protect the cable either.

So using it to boil a kettle whilst doing the ironing, make some toast etc, you have a potential 6kW, ~25a load.

When I was planning on doing a similar thing, but with a fixed installation, the electrician insisted that the double 13a socket needed to be protected with an additional breaker between that and the commando socket.

Now, if it was a 16a commando, then the cable would be protected by the 16a breaker of the commando socket.
 

Adopado

Well-Known Member
Aug 19, 2019
6,829
5,445
Scotland
Just in case you are not playing silly buggers and for those that might think that that cable is a good idea.

The 32a breaker for the commando (assume its 32a as thats what the commando socket is) will not protect the extension cables 2.5mm cable that will be rated at 20 or so amps.

You have a double socket with a total capacity that potentially can exceed the rating of the cable. Whilst a single device may be max 13a fused, 2 devices would potentially exceed the rating of the cable and the individual fuses are rated each too low to be protecting the cable.

With a normal extension cable, its fused in the plug of the extension cable, or sometimes additionally in the extension cable socket. This is what is protecting the extension cable. But in the case of the commando setup, there is no fuse, nor one in your double socket, so the only fuse in play here with the potential to protect the cable is the main circuit breaker, but that's probably rated at 32a so won't protect the cable either.

So using it to boil a kettle whilst doing the ironing, make some toast etc, you have a potential 6kW, ~25a load.

When I was planning on doing a similar thing, but with a fixed installation, the electrician insisted that the double 13a socket needed to be protected with an additional breaker between that and the commando socket.

Now, if it was a 16a commando, then the cable would be protected by the 16a breaker of the commando socket.
Most people don’t understand the purpose of the fuses… and that’s not surprising or unreasonable. Yes, they’re there to protect the cabling not the device plugged into it. (But you hadn’t understood either until your electrician explained that your own proposal needed additional protection…)
 
So using it to boil a kettle whilst doing the ironing, make some toast etc, you have a potential 6kW, ~25a load.
I think this illustrates my point about continuous load of an EV charger vs "normal use". the kettle will only run a few minutes, the iron will run in 30-60 second pulses. While the 2.5mm cable would be under-rated for the ampage, you're likely to get away with it because the loads won't be high for long enough for heat to build up.
With an EV, it's continuous load, somethings which were previously below spec, but worked will instead... melt...
 
(But you hadn’t understood either until your electrician explained that your own proposal needed additional protection…)

I had, but I thought he was going to use the same >32a rated cable that was wired into the commando which cable wise, would not have been an issue as the circuit breaker would have been rated less than the cabling. So was surprised that he still wanted to install a standalone MCB for the twin socket. Which is fine as its his job to meet the regs. I just told him what I wanted where and to what power handling capacity. I still haven't had it installed yet though and tbh, will probably just end up going 16a commando as its just a combined backup charging/occasional double socket use which will never be used at the same time.
 
Last edited:
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PITA

Model 3 Performance
Sep 2, 2021
1,149
1,127
West Midlands, UK
Just in case you are not playing silly buggers and for those that might think that that cable is a good idea.

The 32a breaker for the commando (assume its 32a as thats what the commando socket is) will not protect the extension cables 2.5mm cable that will be rated at 20 or so amps.

You have a double socket with a total capacity that potentially can exceed the rating of the cable. Whilst a single device may be max 13a fused, 2 devices would potentially exceed the rating of the cable and the individual fuses are rated each too low to be protecting the cable.

With a normal extension cable, its fused in the plug of the extension cable, or sometimes additionally in the extension cable socket. This is what is protecting the extension cable. But in the case of the commando setup, there is no fuse, nor one in your double socket, so the only fuse in play here with the potential to protect the cable is the main circuit breaker, but that's probably rated at 32a so won't protect the cable either.

So using it to boil a kettle whilst doing the ironing, make some toast etc, you have a potential 6kW, ~25a load.

When I was planning on doing a similar thing, but with a fixed installation, the electrician insisted that the double 13a socket needed to be protected with an additional breaker between that and the commando socket.

Now, if it was a 16a commando, then the cable would be protected by the 16a breaker of the commando socket.

I do appreciate your attention to this non-event. Maybe protecting those that are boiling kettles, toasting bread and ironing outside... all at the same time.

Chances of me being lucky enough to find me jetwashing my cars, and somebody else mowing the lawn for me at the same time would blow my mind fuse first.

Having checked... my Karcher K4 uses 7.5 amps ... so I'm well within 'home detonation' capacity.

... and as I said, it all works well... and exactly what I bought it for.
 

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