Yesterday at 17:061 day Hello.I have a radial circuit running from a 20a RCCBO from the main consumer unit to a carport about 10m away.It initially runs in 4mm2 t&e then transitioning to 4mm SWA 3 core in a ground duct and then to 4mm t&e clipped to the frame inside the actual structure.On the radial are 2 double sockets and a single socket. Would it be ok to add a 32a commando socket with an interlocked on/off switch to this circuit. Obviously it would never be used to it's full 32a capacity given the RCCBO.
22 hours ago22 hr If you have no plans for it to use 32A, why a 32A Commando and not a 16A one? What are you looking to power?
22 hours ago22 hr 8 minutes ago, garrymartin said:If you have no plans for it to use 32A, why a 32A Commando and not a 16A one? What are you looking to power?Was my thought too until I realised that if you put in a 16A one then you'd need a separate breaker for that as the circuit is 20A.I'm not an electrician but I think you'd be ok to put the 32A in place, but then you should ensure that anything plugged in to that socket can handle 32A. Not a good idea replace a 16A plug with a 32A to just make it work on that outlet. Though I guess once you have one socket, off the shelf adapters (often with breakers) are relatively cheap.
21 hours ago21 hr 6 minutes ago, -rick- said:Was my thought too until I realised that if you put in a 16A one then you'd need a separate breaker for that as the circuit is 20A.You'd be fine to put a 16A Commando on a circuit protected by a 20A RCBO running with those cable sizes. Not sure what you mean by needing a separate breaker?7 minutes ago, -rick- said:I'm not an electrician but I think you'd be ok to put the 32A in place, but then you should ensure that anything plugged in to that socket can handle 32A. Not a good idea replace a 16A plug with a 32A to just make it work on that outlet. Though I guess once you have one socket, off the shelf adapters (often with breakers) are relatively cheap.Yeah, you shouldn't do that. The cable might be sufficient for 32A, but it depends on the actual length and the installation method for the cable. If it was OK, then you'd need to change to a 32A RCBO in the consumer unit. And I'd want an electrician to verify that.I'm just questioning why a 16A Commando socket wouldn't be useful if there is no plan to draw 32A. What's being plugged into it?
21 hours ago21 hr 6 minutes ago, garrymartin said:You'd be fine to put a 16A Commando on a circuit protected by a 20A RCBO running with those cable sizes. Not sure what you mean by needing a separate breaker?No you wouldn't because the plugged in device needs to be appropriately fused. The cable coming out of a 16A commando plug won't be rated for the 20A circuit (nor will the plug/socket). But commandos don't have built in fuses. You need a local breaker if you want to put a smaller rated component on a higher rated circuit.You could change the RCBO to a 16A one to maintain protection but that doesn't seem great.
21 hours ago21 hr The RCBO (MCB or whatever) is there to protect the fixed wiring, not whatever is plugged into it. The current is drawn by whatever is plugged into the 16A Commando, and therefore should only ever be 16A or less (continuously).
21 hours ago21 hr I've looked into this before and I'm pretty sure you can't put 16A commandos on a 32A radial without local protection. Normal UK mains wiring has fuses in the plug, commandos don't.2 minutes ago, garrymartin said:The current is drawn by whatever is plugged into the 16A Commando, and therefore should only ever be 16A or less (continuously).Except in fault conditions (which fuses are supposed to be there to protect against).
21 hours ago21 hr 5 minutes ago, -rick- said:I've looked into this before and I'm pretty sure you can't put 16A commandos on a 32A radial without local protection. Normal UK mains wiring has fuses in the plug, commandos don't.Correct. As above, 20A max.
2 hours ago2 hr Author 18 hours ago, garrymartin said:It's common practice. This is from the latest On Site Guide...Thank you.I assume a 32a socket is also acceptable. I can't see why not.
1 hour ago1 hr 1 hour ago, Beelbeebub said:I assume a 32a socket is also acceptable. I can't see why not.No, it is not. Even if there isn't a specific regulation that prohibits the exact circumstance, it no doubt breaks a number of key design regulations, not least protection against overload current.What do you need the 32A socket for? If, as you note, you won't use 32A, why the insistance on having the 32A socket?I admit it is a confusing area. I mean, people sell 32A sockets to 16A plug conversion leads, so I can see why it might seem acceptable to use a 32a socket in the first place.
1 hour ago1 hr 2 minutes ago, garrymartin said:No, it is not. Even if there isn't a specific regulation that prohibits the exact circumstance, it no doubt breaks a number of key design regulations, not least protection against overload current.Can you expand on this? You clearly have access to the regs and I don't, but why is this different from using a 13A rated plug with a 3A fuse? In this case the 'fuse' being the 20A RCBO.
1 hour ago1 hr 5 minutes ago, -rick- said:Can you expand on this? You clearly have access to the regs and I don't, but why is this different from using a 13A rated plug with a 3A fuse? In this case the 'fuse' being the 20A RCBO.The RCBO is there to protect the circuit cable and the commando socket or 13A socket. The fuse protects the appliance and the appliance cable. They are different things for different purposes.Let me try the question again. Why a 32A socket? Edited 1 hour ago1 hr by garrymartin
23 minutes ago23 min 37 minutes ago, garrymartin said:The RCBO is there to protect the circuit cable and the plug itself. The fuse protects the appliance and the appliance cable. They are different things for different purposes.That doesn't really address my question. Things with a commando socket on them aren't necessarily fused. Neither are domestic fixed appliances (ovens). Both rely on the circuit protection for everything. So my question put another way, why is it a problem to have an outlet that is rated for more current than the circuit would support? This seems to be a common occurrence.
Just now1 min 3 minutes ago, -rick- said:Neither are domestic fixed appliances (ovens)So different then. Fixed appliances with a calculated load and diversity. And a circuit designed to support them?19 minutes ago, -rick- said:So my question put another way, why is it a problem to have an outlet that is rated for more current than the circuit would support? This seems to be a common occurrence.I'd challenge the idea that it's common to have an outlet rated for more current than the circuit can support.What's going to be plugged into a 32A socket? Something that only draws 4A or something that draws 32A? Someone walking up to it would ordinarily and reasonably expect that a 32A socket would be on a circuit designed and installed to support a 32A load.The RCBO is there to protect the circuit. It's not a switch that you should be throwing every time it trips because something you plugged into a 32A socket exceeded the 20A circuit design specification.Like I said though, I'm not an electrician. This is just my interpretation of the regulations and design best practice.Still need @Beelbeebub to tell us why there is a need for a 32A command on a circuit not designed to support that load.
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