Taking a spur off cooker supply

[Hillabaloo]

DIYer question.

I have a 32 amp supply going from consumer unit in garage to kitchen. It supplies an induction hob only. The cable is easily accessible.

I need an additional socket in the garage - 13 amp max. The easiest and hopefully cheapest way to do this is to take a spur off the 32 amp cable.

How should I do this? I will need a junction box and 2.5 mm cable for the 13 amp socket, but how do I do this safely? So for example how can I ensure the 2.5 mm cable is isolated from power going to hob when its on? Recommendations on products would be good also.

Apologies if a daft question.

Thanks in advance.

 

[westward10]

Also, in a previous property I had a cooker isolation switch with an integrated socket to plug appliances. In essence this is what I want to do, but without the isolation switch. What I dont get is why its OK for the switch and socket but not to do a spur.

I have no idea why you want to do this when there is a spare way, none at all.

 

[Hillabaloo]

I have no idea why you want to do this when there is a spare way, none at all.

(1) I thought I needed an electrician to connect to CU and contact building folks. (2) I wanted to do it myself and keep costs to a minimum. (3) I thought there would be a simple solution given the proximity of the cable to the hob.

I do appreciate your input though.

 

[westward10]

1. Find out the cost.
3. There is a simple solution.

 

[timhoward]

What I dont get is why its OK for the switch and socket but not to do a spur.

Electrically they are different ideas.
In short, reducing cable size half way along a run requires adding extra protection which would be a right pain to implement in this situation. (Wrestling 2 x 6 sq mm wires that aren't quite long enough into a fused spur would be rather torturous)
I wouldn't even entertain doing it this way, when it's such a trivial matter to run it into a new MCB (~£3) in the consumer unit. A simple gland in the side, and off it goes.

I'd imagine you could find a sparks that would let you run the cable and leave a couple of meters of cable for him/her to test, connect, and do the required paperwork.

 

[davesparks]

Also, in a previous property I had a cooker isolation switch with an integrated socket to plug appliances. In essence this is what I want to do, but without the isolation switch. What I dont get is why its OK for the switch and socket but not to do a spur.

The cooker switch incorporating a socket is a bit of a legacy item that we just haven't let go of yet. Years ago a single socket was all you needed for the 1 or maybe 2 small appliances you might have and so it made perfect sense to have that socket built in to the cooker switch. At that point in time the regulations were quite strict about the number of sockets allowed on a circuit.
Since then things have changed somewhat, someone came up with the idea of the ring circuit to feed multiple sockets for a start.

As for why the spur is not OK but the socket in the cooker switch is it is partly down to who you are asking. Most active members of this forum are professional electricians and so our answers are based in regulations, best practice and experience.
We have all experienced the ways in which your proposed spur can cause problems in the future, it could be minor issues like getting shouted at for turning someone's Internet off in the middle of a zoom meeting when you thought you were just turning a cooker off. Or it could be the burned out and melted mess we've had to fix because someone connected a bit of 2.5 into 32A circuit wired in 6mm.

If you ask the same question on a DIY based forum you will likely get a different answer, possibly even a step by step guide on exactly how it could be done (which is not permitted on this forum)

Ultimately would you rather take the advice of professionals who know or have experienced all the ways this could go wrong or the advice of someone who's done it a couple of times before and 'it hasn't gone wrong yet'

 

[Hillabaloo]

Electrically they are different ideas.
In short, reducing cable size half way along a run requires adding extra protection which would be a right pain to implement in this situation. (Wrestling 2 x 6 sq mm wires that aren't quite long enough into a fused spur would be rather torturous)
I wouldn't even entertain doing it this way, when it's such a trivial matter to run it into a new MCB (~£3) in the consumer unit. A simple gland in the side, and off it goes.

I'd imagine you could find a sparks that would let you run the cable and leave a couple of meters of cable for him/her to test, connect, and do the required paperwork.

Thanks will follow advice

 

[Hillabaloo]

The cooker switch incorporating a socket is a bit of a legacy item that we just haven't let go of yet. Years ago a single socket was all you needed for the 1 or maybe 2 small appliances you might have and so it made perfect sense to have that socket built in to the cooker switch. At that point in time the regulations were quite strict about the number of sockets allowed on a circuit.
Since then things have changed somewhat, someone came up with the idea of the ring circuit to feed multiple sockets for a start.

As for why the spur is not OK but the socket in the cooker switch is it is partly down to who you are asking. Most active members of this forum are professional electricians and so our answers are based in regulations, best practice and experience.
We have all experienced the ways in which your proposed spur can cause problems in the future, it could be minor issues like getting shouted at for turning someone's Internet off in the middle of a zoom meeting when you thought you were just turning a cooker off. Or it could be the burned out and melted mess we've had to fix because someone connected a bit of 2.5 into 32A circuit wired in 6mm.

If you ask the same question on a DIY based forum you will likely get a different answer, possibly even a step by step guide on exactly how it could be done (which is not permitted on this forum)

Ultimately would you rather take the advice of professionals who know or have experienced all the ways this could go wrong or the advice of someone who's done it a couple of times before and 'it hasn't gone wrong yet'

Thanks Dave. Very interesting. I'll stick to professional advice on this one. I've decided on dedicated supply from CU.

 

[Rockingit]

The cooker switch incorporating a socket is a bit of a legacy item that we just haven't let go of yet. Years ago a single socket was all you needed for the 1 or maybe 2 small appliances you might have and so it made perfect sense to have that socket built in to the cooker switch. At that point in time the regulations were quite strict about the number of sockets allowed on a circuit.

Just tried to do some history on this over a coffee and it's an 'interesting' mystery (wish Lucien was around, I bet he'd have known!).

The relevant British Standard today is BS4177:1992 (and is £138 to read, so that's not happening...) however it's predecessor from 1967 simply refers to the purpose of the socket as "an auxilliary circuit for other devices", rated up to 15A (allowing both formats of BS 546 round pin AND BS 1363). That was a revision of BS1833 from 1952 where the major change was a jump from 30A cookers to 45A cookers (so the concept of a 45A / 11kw cooker has existed now for nearly sixty years - nothing new!!). BS1833 appears to have been born from the legacy DC days of BS438: 1932, no versions of which seem to be online even in the BSi archives - however - the 1967 standard makes reference in the text to the much earlier 1932 version as having used BS 546 for the auxilliary circuit. As BS438 didn't exist until May 1934 one assumes there was a revision at some point.

The bottom line is that we've had an auxilliary circuit on cooker outlets for about a hundred years.

My guess........ As early electric kettles were around from the 1910's as the replacement for gas stovetop ones, logically if you could afford to have an electric cooker installed then you'd not need your gas stovetop kettle anymore but were used to the concept of boiling water at your stove - so you'd buy an electric kettle and it would need adjacent power.

 

[pc1966]

Just tried to do some history on this over a coffee and it's an 'interesting' mystery (wish Lucien was around, I bet he'd have known!).

Alas, Lucian is missed so often

My guess........ As early electric kettles were around from the 1910's as the replacement for gas stovetop ones, logically if you could afford to have an electric cooker installed then you'd not need your gas stovetop kettle anymore but were used to the concept of boiling water at your stove - so you'd buy an electric kettle and it would need adjacent power.

That is my feeling, that if you had just had an electric cooker fitted then you would want an electric kettle but might not have many (if any?) spare 13/15A sockets already.

The 13A plug with internal fuse of course means it is not important if the supply is 16A or 45A, etc. Having a 15A unfused outlet off 30A/45A seems a risk though? Did the oldest has their own rewirable fuse just for the outlet?

For a new kitchen with lots of sockets there is no need for the cooker+outlet fixture, but for many existing kitchens that extra socket is handy!

 

[Rockingit]

Alas, Lucian is missed so often


That is my feeling, that if you had just had an electric cooker fitted then you would want an electric kettle but might not have many (if any?) spare 13/15A sockets already.

Even at members rates it's not worth the money to find out! Old pictures might reveal some clues?

My own thoughts on them are that they're actually a danger - normally fitted adjacent / 'behind/above' a hob, using them means either having a trailing flex or worse, an arm, stretching above a hob.

 

[Rockingit]

The 13A plug with internal fuse of course means it is not important if the supply is 16A or 45A, etc. Having a 15A unfused outlet off 30A/45A seems a risk though? Did the oldest has their own rewirable fuse just for the outlet?

Skip to 22 mins!! Yes - they had internal 15A fuses (although from what time in history I don't know - BS88 was 1967)

 

[pc1966]

Even at members rates it's not worth the money to find out! Old pictures might reveal some clues?

Yes, BSI documents (in fact most of them) are a real rip-off!

My own thoughts on them are that they're actually a danger - normally fitted adjacent / 'behind/above' a hob, using them means either having a trailing flex or worse, an arm, stretching above a hob.

These days maybe, but on the older style with the back plate and (sometimes) high grill they had to be at the side which is sensible place.

 

[pc1966]

Skip to 22 mins!! Yes - they had internal 15A fuses (although from what time in history I don't know - BS88 was 1967)

BS88 dates back to 1919 or so. Just think how low 88 is compared to 1363 that dates to 1947 or so!

 

[Rockingit]

BS88 dates back to 1919 or so. Just think how low 88 is compared to 1363 that dates to 1947 or so!

I thought that was only the larger / HV formats?? NOT an expert in this, just casual interest!

 

[pc1966]

I thought that was only the larger / HV formats?? NOT an expert in this, just casual interest!

The earliest reference I saw was for LV cutouts, but I don't have any of the standards (no need, too high a cost for curiosity) to answer that.

Some day I will hopefully find the time to visit the British Library to take a look for free (sort of)