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| Junctioning 32A cooker circuit with a 13A spur. |
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| paulca:
I bought a new cooker hob and oven. The new cooker hob is gas, but has a 13Amp fused plug on it for the ignitors. The new oven is 16A has a plastic box with screw terminals inside for 6mm2 cable. The incoming power is via a T&E 6mm2 coming from behind a cabinet. This incoming line is isolated with a dual pole 40A isolator in the wall... as it should. And runs to a single 32A OCB (and the shared 100mA general trip). The "correct", by the book, method is to replace the 6mm2 cable and it's outlet with a dual outlet plate (ideally independently fused). Run 6mm2 to the 16A oven and 13Amp round flex to a trailing socket for the hob... or mount it in a cut out of box. Of course a spark will charge me a small fortune for that, given the feed is located behind a kitchen corner unit where the "old" pre-kitchen refit cooker used to be and would need to be pulled to get behind it. So, my "not always to code" Spark who I get to odd jobs and network cabling, advised... A 60A rugby-ball style junction box. 6mm2 in, 6mm2 + stranded flex out. Those boxes have really beefy through tube terminals with 4 screws per tube. He suggests if I strip the 13A flex really far back, fold it over, so it's at least half the length of the terminal, then slide it "underneath" the 6mm and clamp the 6mm2 down on top of it with the terminal screws. My only concern with this is the trailing socket flex is 13Amp. The circuit feeding it is 32Amp. It's not a problem of load, the gas hob pulls less than a watt and very rarely when the ignitors are used. The issue is the 13 amp cable in a 32Amp circuit. Sure the hob is fused, as long as I actually use a socket and retain the plug's fuse. But if something bad where to happen to that socket, like water ingress (it IS a kitchen), or someone put a drill through it, the 32A could melt and set fire to stuff running down that 13Amp cable. I think his response was that this is not worth worrying about and I'd be fine with the flex as long as the plug connected to it is fused. The even lazier approach is to connect the 6mm2 to the new oven and shove the bare tails from the hob in there too. How much damage would 32Amp fault current do to a 13Amp flex before the 32OCB goes? Worth the risk? I mean it's not "inaccessible" and smoke would be noticed. The oven can be pulled in a minutes. |
| paulca:
Is it feasible to consider running 6mm2 through a standard UK wall socket? Would 2x6mm2 fit into the terminals? That way I could stay 6mm2 through out and use the plug socket as the junction box. I know they get used with 30Amp mains rings all the time... but would it be wise to attempt this? |
| david77:
I know nothing about UK wiring rules but I'd do it this way. Put a small ditribution panel behind the kitchen like this https://www.spelsberg.co.uk/small-distribution-boards/ak-compact-3-24te/73540301/ run the 6mm² feed in there and junction it off to an outgoing 6mm² to the oven. Additionally put a B13 MCB in there that goes out to the hob. If there's a fault with the hob the B13 will trip before the 32Amp breaker in the CU. |
| Zero999:
The 13A cable should be fused at 13A. You could connect wire it to the same feed as the oven, via a 13A fused spur. |
| paulca:
Interesting ideal. Assuming I can find room for it. Something like this: https://www.screwfix.com/p/chint-nx3-5-module-2-way-populated-garage-consumer-unit/9864v I can even just use those modules. The gas hob will not use 6A and the cooker is supposed to be a 16A fused appliance anyway. The cavity is pretty tight though. |
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