is 2.5mm2 cable fine from cooker switch to CCU?

[JohnW2]

... In fact, it would save us so much time that we might as well close the forum!

What are you suggesting? That poor advice should be given just to give this forum a life?

It's very tedious to be going over all this ground that had been done to death so many times in the past.

What I am suggesting/implying is that if, for the reasons you have outlined, everyone were to refuse to answer many of the questions we see (with other than "don't do it" or "get an electrician"), then a goodly proportion of OPs will go away and try to muddle through their job with no advice at all - which is not necessarily ideal.

There are, of course, extreme cases in which no sane person would advise anything other than "get an electrician", but many/most of the situations we see are not that extreme.

Kind Regards, John

 

[ericmark]

Back to question. We are permitted 3 meters of cable if unlikely to be damaged to the protective device so if there is a cooker supply then using less than 3 meters of a smaller current capacity cable to feed a fused connection unit (FCU) which in turn feeds an appliance is acceptable.

However remove that FCU and it is not. So with a cooker isolator feeding a double cooker connection unit all with 6mm² and then a 6mm² to hob and a 2.5mm² to FCU and from that to oven is OK.

But if the oven was over 3kW then once you miss out the FCU then supply to oven will need to be in 6mm². This all assuming a 32A MCB/Fuse/RCBO at consumer unit.

So with an oven over 3kW we have a major problem, either one uses cable which is too thick to fit in many of the terminal blocks or you have to swap the device in the consumer unit/fuse box for a smaller one to match cable. With a 25A MCB then there is a problem will it be large enough to supply both the oven and hob?

There are specials the HCN510 Induction Hob is designed to work on a 13A supply and if you were using that model then a 25A MCB for oven and hob would not be a problem.

The other problem is the oven or hob recommendations going to the ridiculous even if you could get the cable in the terminals feeding a oven or hob with a 100A supply should something go wrong the appliance would likely go up in flames before the fuse would blow so each manufacturer should stipulate the size of the protective device. Where not stipulated we assume 32A.

In resent years there has been a move to using larger cable and larger protective devices using a 45A supply to feed my stand alone cooker is all well and good but to supply an oven with 45A when it only requires 16A is clearly going OTT.

What we have needed for some years now is a FCU to take a 16A fuse to allow us to use equipment designed for the rest of Europe but as far as I know there has not been one made.

It is of course true that all installations should be inspected and tested but back in 1998 when I went to work for a firm installing domestic cookers I was as an electrician not provided with the meters required to do those tests. Only in 2004 when Part P came in and electricians had be be scheme members did electricians get provided with the correct tools for the job.

In 2008 the installation rules changed and RCD protection become more widespread so even if there are faults like those which killed Emma Shaw were to happen in a post 2008 installation the RCD would trip before anyone was injured.

I am not saying fitting anything without testing is OK it is not, and it has never since the introduction of BS7671 been OK, but with care and some understanding 99% of the time we get away with it.

 

[Essex1]

Back to question. We are permitted 3 meters of cable if unlikely to be damaged to the protective device so if there is a cooker supply then using less than 3 meters of a smaller current capacity cable to feed a fused connection unit (FCU) which in turn feeds an appliance is acceptable.

However remove that FCU and it is not. So with a cooker isolator feeding a double cooker connection unit all with 6mm² and then a 6mm² to hob and a 2.5mm² to FCU and from that to oven is OK.

But if the oven was over 3kW then once you miss out the FCU then supply to oven will need to be in 6mm². This all assuming a 32A MCB/Fuse/RCBO at consumer unit.

So with an oven over 3kW we have a major problem, either one uses cable which is too thick to fit in many of the terminal blocks or you have to swap the device in the consumer unit/fuse box for a smaller one to match cable. With a 25A MCB then there is a problem will it be large enough to supply both the oven and hob?

There are specials the HCN510 Induction Hob is designed to work on a 13A supply and if you were using that model then a 25A MCB for oven and hob would not be a problem.

The other problem is the oven or hob recommendations going to the ridiculous even if you could get the cable in the terminals feeding a oven or hob with a 100A supply should something go wrong the appliance would likely go up in flames before the fuse would blow so each manufacturer should stipulate the size of the protective device. Where not stipulated we assume 32A.

In resent years there has been a move to using larger cable and larger protective devices using a 45A supply to feed my stand alone cooker is all well and good but to supply an oven with 45A when it only requires 16A is clearly going OTT.

What we have needed for some years now is a FCU to take a 16A fuse to allow us to use equipment designed for the rest of Europe but as far as I know there has not been one made.

It is of course true that all installations should be inspected and tested but back in 1998 when I went to work for a firm installing domestic cookers I was as an electrician not provided with the meters required to do those tests. Only in 2004 when Part P came in and electricians had be be scheme members did electricians get provided with the correct tools for the job.

In 2008 the installation rules changed and RCD protection become more widespread so even if there are faults like those which killed Emma Shaw were to happen in a post 2008 installation the RCD would trip before anyone was injured.

I am not saying fitting anything without testing is OK it is not, and it has never since the introduction of BS7671 been OK, but with care and some understanding 99% of the time we get away with it.

GASP!

 

[ban-all-sheds]

it's not rocket science if you're willing to learn..

Indeed it is not.

But the learning MUST happen before any doing.

 

[333rocky333]

Good thought - but, unfortunately, those MF JBs (and I'm not aware of any others) will not take (are not meant to take) 6mm² conductors.

NOT that i would recomend them but wago do bigger push on terms they quote as maintenance free, coupled with there MF wago enclosure technically would be ok, i suppose.

 

[JohnW2]

Good thought - but, unfortunately, those MF JBs (and I'm not aware of any others) will not take (are not meant to take) 6mm² conductors.

NOT that i would recomend them but wago do bigger push on terms they quote as maintenance free, coupled with there MF wago enclosure technically would be ok, i suppose.

Yes, that's true. Although a good few people still seem to be sceptical, Wago claim (click here) that 773-173 Wago connectors (which will take 6mm² conductors) in a Wagobox can comply as 'maintenance free' per BS 5733.

Kind Regards, John