Hi Group
Can anyone advise me on the correct type of cable and the size to wire a cooker 6Kw and a hob 6Kw to the cooker isolating switch. Should this be some kind of flexable cable? Does part P allow me to connect directly from the switch to the appliance? All help greatly appreciated.
Graham
Quick answer: 6mmsq cable; no, not flex. Ass-U-ming your cooker isolating switch is fed by a dedicated circuit from the consumer unit, with its own MCB/fuse rated at 30A/32A/40A.
Both the hob and the cooker (I ass-U-me you mean oven?) ought to be within 2m of the cooker switch - the idea being that you (and anyone else, even Just Passing Through the kitchen) can readily see and operate the isolator quickly in the event of a cooking fire or other fault. If significantly beyond that distance, put another isolator closer to the one that's far away, wired either in series with the 'main' cooker switch, or with its feed run from the incoming (permanantly live) side of the cooker isolator.
Let us know if you need more detail - Stefek
With all the authority of one who's recently been corrected by Andy Wade
- you're wrong ;-) For *domestic* use it's sanctioned by the Regs to treat the *design* current as the 'diversified' figure of 10A +
30%-of-the-rest; so your 12kW of cooking appliances - which the OSG specifically says is OK to treat as one appliance - will pull 52A using the fiction of a 230V supply, which we downrate to 10 + (42*0.3) = 22.6A. You'd be 'allowed' to use 4mmsq (hell, even 2.5mmsq with charitable assumptions about cable routing!), but the 6mmsq I suggested is the 'usual' answer, which allows for the peak loads without even warming noticeably (since they don't last for more than a couple of minutes).HTH - Stefek
I follow up my own posting (tsk, tsk) to stress again that this application of diversity is appropriate ONLY for 'domestic' usage, or wot the OSG heading calls 'household or similar premises'. It's based upon normal home cooking practice, and would NOT be sensible if you were regularly cooking up batches of [marmalade, soup-run soup, bike chain grease].oneof() making heavier-than-usual use of all the cooking elements.
Stefek and Dale
Many thanks. Just to be sure the current configuration is 6mmsq TE from consumer unit (fused 40A) which is 2Mtrs away from cooker switch. From cooker switch to oven and hob I have 2 separate 4mmsq TE each 1.5 Mtrs long. Can I ask one final time should the cable to the oven and hob be the same stuff I wire my ring main with? Sorry to labour this point but someone told me this stretch of cable should be flexable i.e. a stranded make up.
Thanks again Graham
In fact the OSG (not BS7671) says this [p.154]:
"A 30 or 32 A circuit is *usually* appropriate for household or similar cookers of rating up to 15 kW."
I've emphasised the "usually" - for (hopefully) obvious reasons.
=
The stuff from the switch to the oven and hob should be 6mm. Because that is the conductor size for this 40A circuit. Even if the circuit has a 32A MCB then by the book the cables would have to be 6mm as there should be protection wherever a cable changes size.
Both 4mm2 and 6mm2 cable have stranded conductors although the earth wire in the 4mm2 is usually a single solid wire.
It is quite wrong to use ring main cable 2.5mm2 in this case.
If I've got something wrong someone will tell me I hope.
The manufacturers installation instructions should tell you what cable to use. I had to use
Adam
Hi Stefek , Dale and ARWadsworth
Well it appears this was not to be my last request for clarification as the cable shown in the above link is a flexable cable with many thin strands of copper in each wire. The wire I currently have to the oven and hob is the same as used for the connection from the consumer fuse box to the isolating switch. This has only 7 very thick copper strands in each wire and is very difficult to bend for the connection to the appliances. Sorry guys but could you please clarify.
Regards Graham
The protection at the consumer dictates the gauge of cable used. If the fuse in the fuse box is 32 Amps rated, then the cable from that supply must be able to take 32 Amps current along its full length. If you reduce the gauge of cable being supplied from the fuse in the fuse box, then you also have to reduce the rating of fuse to suit the cable.
When you need to reduce the gauge of cable being supplied from a larger gauge, then you need to install a protective device that is able to withstand the heavier current, but can be fused to suit the lower gauge cable paths spurred from it. Something like a Fused Connector Unit that can easily withstand the 32 Amps current rating, but can fitted with a 13 Amps rated fuse for the loads taken from it.
The fuse or safety breaker device in the consumer unit protects the cable, not the appliance if the appliance is a lower rated current device.
Get it?
Having said all that, the number of strands in the cable only really affects the flexibility of it. The cross sectional area affects the current handling capacity.
I'd choose the more flexible cable when running to a free standing cooker, or to something like an industrial dishwasher that may well move about a fair bit.
Solid core (in practice often a-few-strands) like you have is often used for cookers. As long as the rating is right either should be OK for a built in oven/hob. Solid is cheaper than flexible stranded stuff.
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