32A Industrial socket for cooker?
- Thread starter DIYbot2
- Start date
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Inrush current
I don’t deal with MCB’s a lot (hence the mis-acronym when I wasn’t thinking about it) but I do know it’s a miniature circuit breaker. I have a masters in electrical engineering and some practical experience of DiY circuits, especially for amps and power supplies. I’ve assisted an electrician with laying cables and done things like changed light fittings, But hands on experience with this specifically is pretty limited.
Ignoring the phase bit (see above) It wouldn’t be very visible, so that’s not that relevant
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My first question it how often do you think you'll be using this? If this is for regular use then I'd be thinking it may be commercial and therefore be paying commercial rates on the property and therefore the goal posts change and unshuttered sockets may be permitted.
OK that over; why do you think You will need to upgrade to a type D MCB? this is only a 4KW device so running current <18A. Assuming an inrush of 10x18=180A a 32B will hold that for at least 10 seconds (I haven't looked it up but it feels right).
The circuit design calculations would need to be done to see if it could even be within regs to be changed to a C or D type.
I assume there is RCD in there somewhere or RCBO (a picture of your consumer unit would be handy) and on that basis I personally would suggest something like this;
fitted with a 2 pole B32 MCB where you need it would be your best option. The next thing would be feeding the cable to it and quite honestly if the existing cooker feed is at least 6mm² (minimum for 40A MCB) I don't think any rules would be broken to simply connect this to the live side of the cooker switch. Even if the mixer is running there will be >4KW left for the cookerwhich will probably be plenty for 'everyday use'.
The 3 phase converter may very well have the facility for a soft start with the advantage of a significantly reduced inrush and you may be able to use a B25 or even B20 MCB.
Another alternative to the 3phase converter would be to replace the motor with a single phase version and the manufacturers may even offer the option.
OK that over; why do you think You will need to upgrade to a type D MCB? this is only a 4KW device so running current <18A. Assuming an inrush of 10x18=180A a 32B will hold that for at least 10 seconds (I haven't looked it up but it feels right).
The circuit design calculations would need to be done to see if it could even be within regs to be changed to a C or D type.
I assume there is RCD in there somewhere or RCBO (a picture of your consumer unit would be handy) and on that basis I personally would suggest something like this;
The 3 phase converter may very well have the facility for a soft start with the advantage of a significantly reduced inrush and you may be able to use a B25 or even B20 MCB.
Another alternative to the 3phase converter would be to replace the motor with a single phase version and the manufacturers may even offer the option.
It was potential inrush current to the phase converter that I was worried about, rather than the mixer itself. I’ve had a look for soft start phase converters and aren’t seeing much. Potentially I could make my own soft starter for it.
Regarding wiring this on the live side of the cooker switch, I thought the cooker had to be on its own circuit back to the fuse box MCB (hence the swappable socket so that when the cooker was plugged in it was on its own circuit)?
Regarding wiring this on the live side of the cooker switch, I thought the cooker had to be on its own circuit back to the fuse box MCB (hence the swappable socket so that when the cooker was plugged in it was on its own circuit)?
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It merely has to be on an 'adequate circuit', without any other restrictions.
Kind Regards, John
Ah, ok. Thank you, that’s very good to know. The cooker is against an outside wall. If I were to wire off the live side of the switch, would that then be ok to take through the wall and mount a new external 32A socket on the outside wall (possibly also a 16A socket) for additional utility? This would actually be much more convenient.
I thought BS7671 said that heating appliances over 2kw and any appliances over 3kw should be on their own circuit?
BS 7671 itself does not say that. The guidance in Appendix 15 (hence not 'a regulation') does say that, but only in the context of saying that such an appliance should ideally not be connected to a ring final. However, there are some potential issues which I'm about to mention to the OP.
Kind Regards, John
You're welcome.
Although, as you know, there is an issue regarding the acceptability of such a socket in a domestic installation, one good thing about your proposal to use a 32A plug/socket was that it would ensure that both the cooker and mixer (or anything else) could not be used simultaneously (which the circuit may well not be man enough for).
If, as you now suggest, you wire additional (32A and/or 16A) sockets to the circuit, then that possibility of 'simultaneous usage' would return and, ideal, you would have a 'changeover switch' which directed the circuit to either the cooker OR the socket(s) (but not both).
However, I think that the arguable 'non-acceptability' of the 32A/16A sockets applies to anywhere in a domestic installation, so would probably still be the case if the sockets were 'outside'.
Kind Regards, John
Thanks again John. A switch to select either of the socket circuits is a good idea.
Reading this thread
www.electriciansforums.net
it sounds like an interlocked switched socket such as
would meet the regulations.
Reading this thread
I want a 16 amp socket in the garage with 3 double sockets
Glad you got it resolved.
www.electriciansforums.net
it sounds like an interlocked switched socket such as
32A 2 Pin + Earth 230V Interlocked Switched Socket IP44
Suitable for small commercial and industrial applications
www.cef.co.uk
would meet the regulations.
It would - but it would probably be a pretty 'chunky' (and probably not inexpensive) thing.
AS you've probably seen that is open to debate. In terms of electrical common sense, it probably offers at least as much protection as does a shuttered socket, but, strictly speaking, one probably cannot get away from the requirement of the regs for a shuttered socket (without suggesting that an 'interlocked' one is an acceptable alternative).
However, as you undoubtedly know, compliance with 'the regulations' is in no way 'mandatory'.
Kind Regards, John
DIYbot2 said:
A D-curve MCB is very demanding of the circuit/cable concerned. The maximum permitted 'loop impedance' (both internal and external to your property, all the way back to the supplier's transformer) is 0.34Ω for a D31 and 0.27Ω for a D40 -but even the external loop impedance alone may be as high as 0.35Ω if you have a "TN-C-S" supply or 0.8Ω if you have a "TN-S" supply.
Hence, even if the external part of the loop impedance is less than those 'maximum' figures (if not,a D-curve MCB could not be used at all), it would leave little, if any impedance to come from the cable - so that the cable may well have to be larger than the 6mm² which I believe you have. Each metre of 6mm² cable would add about 0.0073Ω to the total loop impedance - so, for example, 10 metres of cable would add about 0.073Ω.
Kind Regards, John
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