Cooker connection unit

[Mrmells]

Hi all

Just a question about fitting a DP switch for a hob and oven.

When we moved into our house, we kocked a wall down in which was part of the cooker circuit attached to a cooker connection unit. The cable has now been shortened and resides between the floorboards! Is this acceptable - its not attached to anythig, it just sits inbetween the boards.

If this isn't correct, what needs to be done to correct it. Also, A bloke fitted the cooker; it is a hob and an oven. The cooker circuit is a 10mm TE cable, it goes to the connection unit and from this unit comes 2 x 2.5TE cable to the oven and hob. Again, is this ok?

One other question. As the bloke connected these to cables straight to the cooker, there isnt a switch above the worktop to isolate the oven and hob. Would it be acceptable to fit 2 45amp DP switches for each appliance (oven & hob) above the worktop?

Any comments would be gratefully be received.

Cheers
M

 

[riveralt]

A bloke fitted the cooker; it is a hob and an oven.

Was this bloke an electrician? If he is then get him back to do a proper job. He should have left you with a minor works certificate and you should have received a Building Control notification from the competent persons scheme he belongs to - or failing that the LA BC officer.

The cooker circuit is a 10mm TE cable, it goes to the connection unit and from this unit comes 2 x 2.5TE cable to the oven and hob. Again, is this ok?

That would depend on a number of factors. What is the size of the MCB protecting the circuit - is there additional protection from an RCD? What is the rating for the oven and hob? Your 'bloke' will have worked all this out when he decided to use those size cables.

A bloke connected these cables straight to the cooker, there isnt a switch above the worktop to isolate the oven and hob. Would it be acceptable to fit 2 45amp DP switches for each appliance (oven & hob) above the worktop?

So you recognise there is something wrong here.

Assuming all the calculations are correct - you would need a 45 Amp DP Cooker Switch and a dual appliance connection unit. The 10mm cable should run from the appropriately sized MCB to the Cooker Switch - I cannot figure out how it gets there from your Consumer Unit - it sounds like it comes up in the middle of the floor - which is not right.
From the Cooker Switch a 10mm cable runs to the dual appliance connection unit and then two cables of the appropriate size run to the oven and hob - I will assume they are separates.

 

[Mrmells]

Hi

Na, he wasn't an electrician!!

Thanks for the feedback mate.

The oven is 4700W and the hob 6000W and the circuit is connected with a 30a mcb at the consumer box. The cooker connection unit and the cooker circuit is run through the floor boards above the kitchen. If the calculations are correct, is it acceptable to leave the consumer unit inbetween the floor boards? What about the 45a DP switches. Can I have one for each appliance - hob and cooker so that I can isolate one or both at a time if need be?

Any comments will be gratefully received.
Cheers
M

 

[riveralt]

Hi

Na, he wasn't an electrician!!

Do you know that is hard to believe

The oven is 4700W and the hob 6000W and the circuit is connected with a 30a mcb at the consumer box. The cooker connection unit and the cooker circuit is run through the floor boards above the kitchen.

After diversity with a 10mm cable 10.7kw equates to around 21Amps without a socket in cooker switch and 26Amps with one - so your 30Amp MCB is okay and your 10mm cable is okay. But.....

If the calculations are correct, is it acceptable to leave the consumer unit inbetween the floor boards?

It doesn't matter about the calculations your consumer unit, if that is what you really mean, should not be inbetween floorboards. Look here to see what you should have

http://www.ultimatehandyman.co.uk/diy_electrics_cooker_circuits.htm

What about the 45a DP switches. Can I have one for each appliance - hob and cooker so that I can isolate one or both at a time if need be?

if you follow the advice I gave you earlier regarding a single Cooker Switch (45Amp) with socket like this http://www.screwfix.com/prods/63376...ree-Range/Crabtree-45A-DP-Sw-13A-Skt-Slimline
which should be located within reach of the oven and hob but more than 300mm from it - and the dual appliance connection unit which connects your 10mm from the cooker switch and looks like this

http://www.alertelectrical.com/prod/1022/click-45a-easyfit-dual-appliance-outlet-plate

With regard to the 2.5mm cable currently connected to your oven and hob you need to be guided by what the manufacturers instructions say, but I would say you will need a minimum of 4mm cable for each device.


And finally, don't forget to inform Building Control before you start this work.

 

[MalcofArabia]

Hi Riveralt that link you posted not sure if you have noticed this on it

"If you are installing a cooker circuit from new, then you need to choose a CCU (cooker connection unit). These are available with or without a socket outlet, it is preferable to get one that does not contain a socket outlet as electric cookers (ovens especially) are notorious for earth leakage. This means that ideally a cooker / oven should be connected to the non RCD protected side of the consumer unit or else nuisance tripping can occur. If you do get one with a socket outlet then the cooker must be wired to the RCD protected side of the consumer unit!"

Not sure that is perhaps the best advice that site as given, espicially if the cable is buried and will come under Reg 522.6.6.

It also shows a diagram of a single CCU controling 2 cooking appliances, While there is nothing wrong with that providing you use the OSG Pg 160 section 8.4 as a guide, I'm worried that quite a few modern ovens now come with cable and 13amp BS 1363 plug tops fitted as they are under 3kw in rating and therefore can plug into a normal socket.

That may lead to someone thinking that a 2.5mm^ is sufficient to feed the oven from the CCU. But then you would have the situation of that 2.5mm^ cable being protected by the 30/32 amp protection device in the main CU, as most CCU units don't have the capability to fuse down.

I hope you don't think I'm trying to br critical and if I'm wrong then I apologise but some of the advice given there does not come up to the advice you gave

 

[ajrobb]

The cooker circuit is a 10mm TE cable, it goes to the connection unit and from this unit comes 2 x 2.5TE cable to the oven and hob. Again, is this ok?

First, I declare I am a novice. My interest is that I have a kitchen to install in a few months.

If it is rated at 240V at 4700W, then it is 19.5A. I suppose it should designed for the maximum European voltage (243.8V). That fits, a resistive load of 4700W at 240V would draw 19.9A at 243.8V.

Hopefully the 6000W hob is rated at 240V. That would be 25A, which is OK for some installations of 2.5 mm² T+E but you'd need to find a 25A CB. However, if it is rated at 230V, that would be 26A. At 240V, that could be just over 27A, which would put it just over the limit for 2.5 mm² T+E.

The oven and hob manufacturers' instructions should state what the maximum size CBs are to protect internal wiring. For instance, if the oven manual states 20A, then you have to go with that. It seems to be fairly common to wire hobs in 4 mm² on a 32A CB, but you must follow MI.

The 10 mm² circuit could be good for a 45A CB. That should be OK. If the cable has been run together with others, it might only be capable of 40A, which might be adequate if you don't run the oven and hob flat out at the same time. Connections to a cable under the floor probably can't be inspected, so might need to be crimped rather than using large screw terminals.

Unless you get a competent person in to do this work, I'd be surprised (even horrified) if a Building Inspector would sign it off.

 

[riveralt]

Hi Riveralt that link you posted not sure if you have noticed this on it

"If you are installing a cooker circuit from new, then you need to choose a CCU (cooker connection unit). These are available with or without a socket outlet, it is preferable to get one that does not contain a socket outlet as electric cookers (ovens especially) are notorious for earth leakage. This means that ideally a cooker / oven should be connected to the non RCD protected side of the consumer unit or else nuisance tripping can occur. If you do get one with a socket outlet then the cooker must be wired to the RCD protected side of the consumer unit!"

Not sure that is perhaps the best advice that site as given, espicially if the cable is buried and will come under Reg 522.6.6.

Accepted - the OP had described that his CU was inbetween the floorboards I was verbally trying to get him to understand and describe to him how the layout should look. The link gave him a broad picture of where the CU fits into the circuit - I should have re-enforced the fact that this is not necessarily how it should be done.

It also shows a diagram of a single CCU controling 2 cooking appliances, While there is nothing wrong with that providing you use the OSG Pg 160 section 8.4 as a guide, I'm worried that quite a few modern ovens now come with cable and 13amp BS 1363 plug tops fitted as they are under 3kw in rating and therefore can plug into a normal socket.

The way the OP was describing his current arrangement and the power ratings given for the oven and hob I feel it is unlikely that a 13Amp plug would be used - which is why I directed him toward the dual appliance kit - I also told him to be guided by his MI.

 

[riveralt]

First, I declare I am a novice. My interest is that I have a kitchen to install in a few months.

If it is rated at 240V at 4700W, then it is 19.5A. I suppose it should designed for the maximum European voltage (243.8V). That fits, a resistive load of 4700W at 240V would draw 19.9A at 243.8V.

Hopefully the 6000W hob is rated at 240V. That would be 25A, which is OK for some installations of 2.5 mm² T+E but you'd need to find a 25A CB. However, if it is rated at 230V, that would be 26A. At 240V, that could be just over 27A, which would put it just over the limit for 2.5 mm² T+E.

The ratings for the Oven and Hob can be added together Hence the 10.7kw which gives 46.5Amps (17th edition works to 230v). Then apply diversity and you end up with a figure of 21Amps without a socket in the cooker switch and 26Amps if one is fitted. The next size up for the MCB in this case is 30Amps - so we use that. The Current Carrying capacity of the cable must be more than the MCB - for 10mm using reference method C is 63Amps so the cable used/proposed is fine.

The oven and hob manufacturers' instructions should state what the maximum size CBs are to protect internal wiring. For instance, if the oven manual states 20A, then you have to go with that. It seems to be fairly common to wire hobs in 4 mm² on a 32A CB, but you must follow MI.

If you follow this assumption then every oven and hob will be wired separately back to the CU - which is a waste when we have a 10mm cable in situ.

The 10 mm² circuit could be good for a 45A CB. That should be OK. If the cable has been run together with others, it might only be capable of 40A, which might be adequate if you don't run the oven and hob flat out at the same time.

10mm cables when enclosed in conduit on a wall or in trunking etc are rated at 52Amps and when enclosed in conduit in an insulated wall is rated at 43Amps.

Unless you get a competent person in to do this work, I'd be surprised (even horrified) if a Building Inspector would sign it off.

Agreed

 

[ajrobb]

(17th edition works to 230v)

-10%/+6% (207V - 243.8V)

The oven and hob manufacturers' instructions should state what the maximum size CBs are to protect internal wiring. For instance, if the oven manual states 20A, then you have to go with that. It seems to be fairly common to wire hobs in 4 mm² on a 32A CB, but you must follow MI.

If you follow this assumption then every oven and hob will be wired separately back to the CU - which is a waste when we have a 10mm cable in situ.

They'd only need to be wired to a CU. I don't understand why there isn't a dual appliance connector that includes local CBs. (I contacted Honeywell and they don't make one.)

 

[JB666]

A CB in a DP cooker outlet would be bliss but untill that happens you can have a DP outlet with one cable run from there to the hob and the other outlet supplying a separate 13A switched FCU for the 13A oven innit You can keep the 10mm flowing right from the MCB/RCBO, through the cooker switch and on to the hob/FCU (which will fuse down for the smaller oven cable or anything else that may get connected at any point in the future)