Spur off cooker circuit

[tomsavage]

I have been reading with interest the many postings about cooker circuits, and whether or not these should be used for anything else. If I understand what I've read, I would summarise as:

1) cooker circuits are best used only for cookers, however,

2) there is a provision in the relevant regs for an additional 'point', e.g. the 3pin socket often found on cooker isolation switches.

3) as an alternative to the combined 'cooker switch and socket' arrangement, it is permissible to have a single spur off the cooker circuit, as long as a) it runs through a suitably rated FCU and b) the spur is no longer than 300mm.

4) There seems to be mixed views on whether the same rated cable needs to be used for a) the whole spur, b) just up to the FCU, c) not at all.


Assimilating the above (rightly or wrongly) I have just wired in a spur to my cooker circuit. The circuit is currently wired in 6mm2, and has a 30amp fuse on the CU. I have thus used 30amp connector block to break into the line and spur off to a suitably-fused switched FCU which will run the extractor hood. The only unusual thing about the way I've done it is that I've used a deep, single-gang box to contain both the connector block and the switched FCU. In other words, from the surface it looks like a normal FCU, but it actually contains a very short spur and the cooker circuit continues on to the cooker.

I've done a rather poor diagram, which may or may not help to illustrate what I've done, but I'm having trouble uploading it, watch this space...

Anyway, any thoughts on the safeness, conformity of this arrangement would be appreciated.

 

[securespark]

Being brought up on the 15th, I don't think you should add anything to the cooker radial.

But the regs say you can, as long as the circuit will stand the total load, and you use cable rated to the device in the board. If you fuse down, then you can decrease the size of cable.

 

[keyplayer]

Being brought up on the 15th, I don't think you should add anything to the cooker radial.

Unless of course you're a kitchen fitter, then it seems perfectly acceptable to wire your 13 amp under top oven to the same junction box as your hob.

 

[tomsavage]

Thanks securesparks. So it seems my arrangement does not contravene regs although it is not to everyone's liking. For what it's worth, I've not managed to upload my dodgy drawing.

The only possible objection some might raise is that the short (about 5cm) link between the connector block at the FCU terminals is in 2.5mm2 rather than 6mm2. However, I would struggle to get two 6mm2 into the connector block, and as the spur is immediately fused down by the FCU, I hope this does not matter.

 

[securespark]

All cables attached to that 30A (or 32A) device need to be rated as such.

 

[keyplayer]

Isn't 4mm to hood a bit ott?

 

[tomsavage]

Oops yeah, sorry, is 2.5mm2 to the extractor.

So securesparks, are you saying that the little link between connector block and FCU needs to be in 6mm2? Is that required by regs or is it best practice?

Gonna be pretty hard to squeeze two 6mm2 cables into the connector block

 

[Pensdown]

The link can be in 2.5mm.

A few weeks ago someone posted a picture of a cooker CCU with a spur for the extractor built in. I think it was Softus but I can't find the post.

Edit. On your drawing you don't need the connector block. You can put the 2no 6mm cables in the supply side of the FCU and use that as the joint. If you use MK/Crabtree although it's tight they will fit in the terminals

 

[plugwash]

So securesparks, are you saying that the little link between connector block and FCU needs to be in 6mm2?

probablly not (its no worse than a 2.5mm ring spur) but you'd need to know the PSCC and use the adibetic equation to be sure.

 

[Pensdown]

So securesparks, are you saying that the little link between connector block and FCU needs to be in 6mm2?

probablly not (its no worse than a 2.5mm ring spur) but you'd need to know the PSCC and use the adibetic equation to be sure.

Your confusing me now. The FCU has a 13amp fuse in it so the cable feeding it can be 1.5mm What has the PSCC got to do with it?

 

[plugwash]

there was a long discussion about this recently.

i don't remember the details but the bottom line was if your cable is rated lower than the device that gives it short circuit protection then the normal getout doesn't apply and you have to calculate the adibetic.

to calculate the adibetic you need to know the PSCC and the let through details of the protective device.

 

[Pensdown]

I can now understand what your talking about although it's unlikely to be relevant for this post.

 

[tomsavage]

Thank you very much for all the helpful info. After reading the post about *all* cabling being in 6mm2, I spent an hour manhandling 2x6mm2 into the connector block, before noticing Pensdown's suggestion about just using the FCU terminals... GRRR, why are the most obvious things so hard to think of... Thanks again.

If anyone is still willing to respond to this thread, I wonder if you could comment on this arrangement:

[imghttp://www.people.ex.ac.uk/tpsavage/diagram2.gif[/img]

In other words, I'm slightly pushing the envelope by including a spur for the gas hob ignition. I know that elsewhere on this forum the usual recommendation is to spur off the ring main for the ignition, but I really want to avoid having yet another isolation switch above the worktop, especially as it for something as minor as the hob ignition. The arrangement above would mean that the single cooker switch would isolate the igntion and the oven.

I guess some would say that running the extractor and ignition off the cooker circuit could overload it but:

1) The spurs for the ignition and the extractor both use FCU's not ring main sockets, therefore there is no way that in the future someone could plug something in and overload the circuit.

2) The combined drain of the extractor and the ignition are well below the potential drain of a "cooker switch with socket" arrangement.

The daft thing is, I am installing a '13amp ring main type' single oven, so it will all be well below the rating of the circuit anyway.

 

[tomsavage]

oops. Try again with the image...

 

[Steve]

The daft thing is, I am installing a '13amp ring main type' single oven, so it will all be well below the rating of the circuit anyway.

yes, this is daft, it needs to be protected by a 13A fuse.