Electrical installation question for inset hobs and 2 ovens.....

[Stephen]

Right,

We are changing the range cooker to:

a 6 gas ring hob which has a 13A cable and plug to power the gas ignition system.

2 seperate gas single ovens/grills. (these are fully gas for the grill and oven parts) These will be installed side by side under the 6 ring gas hob mentioned above.

This means we can have two ovens, or two grills or one grill and one oven at any one time for dinner parties.

Each one of these gas grill/ovens also has a mains lead with a 13A plug on it to power the clocks and gas ignition system.

Above all this is the extractor fan, which again has a mains lead and plug on it.

Now I have a 32A cooker circuit. This currently goes to a 45A DP cooker switch.

Now my two questions are:

1. Is it acceptable to run 6mm2 cable from this double pole switch to a triple gang wall socket behind the cooker so that I can plug the gas hob in and the two seperate grils/ovens into?

1. Is it acceptable to power the cooker hood from the cooker circuit rather than from the kitchen ring fing circuit? Again this would be via a 13A fused neon spur. My reasoning is that the cooker hood fan and light only really gets used when cooking takes place......

[Tim Watts]

If it is a 32A MCB/30A fuse in the CU for this circuit, then yes - it's a 32A radial which is "standard", albeit uncommon. You can hang as many sockets off it as you like - only problem is the 6mm2 cable means you'll only get one set of cables into a socket unless you split with a junction box.

However your triple socket is unlikely to support a combined load of 32A

- more like a total of 20A if it's anything like most double sockets. You'll need a deep backbox too for the cable as it's nearly as flexible as rebar.

[Stephen]

OK, what about the following then:

run 6mm2 cable from cooker switch down to a junction box, fit two lots of 6mm2 cable from this junction box to a double socket each. Then plug the two gas ovens into one of the double sockets and then plug the hob and extractor fan in the other double socket?

Regards

Stephen.

[Tim Watts]

It is arguably possible to run 2.5mm to each socket (but only one socket or double socket per cable) from the JB as the plugtop fuse protects the preceding cable against overload. As no double socket is rated > 20A total, this is within limits for most installation methods of 2.5mm2.

I'm not sure if that's *totally* regs compliant, so I'll wait for one of the resident experts to comment - however, it is in principle no worse that any other spur done in 2.5mm2. In this case, it is merely a spur off the end of a distribution circuit.

[ARW]

What does the cooker switch feed ATM? Does it not feed a cooker outlet plate?

[Tricky Dicky]

The current draw of each of these units is going to be quite small if all t hat is being powered is the ignition, clocks, lights and indicators. The fa ct that they are supplied with 13A plugs means they can be plugged into any ring main socket and do not need a dedicated cooker circuit. If however, y ou do wish to have a single switch to to turn the lot off and you do not w ant someone in the future to mistakenly think it is a 45A cooker circuit us e a 20A double pole switch on the ring main and spur off that.

Richard

[Stephen]

it currently feeds a range cooker, we are essentially replacing a single free standing range cooker with 3 seperate cookers comprising of a gas hob and 2 off gas ovens & grills, along with the cooker hood.

[Stephen]

I am trying to preserve integrity and/or diversity within the kitchen, I already have 4 separate circuits going to the kitchen.

a ring main final circuit ground floor lighting smoke & CO detectors circuit and of course the 6mm2 32A RCBO protected cooker circuit.

The reason why I want to put the two gas ovens/grills, hob and cooker hood on to the 32A 6mm2 RCBO is for two reasons:

the first is we can still cook if the ring circuit pops in the kitchen, and vice versa with a microwave & kettle if the cooker circuit pops.

The second is that it makes life easy if in the future we wish to rip all the gas cookers out and go for an all electric cooker so hence I wish to retain and use the cooker circuit.

I appreciate the current draw is very low on a gas cooker.

[Stephen]

as its a free standing range, its simply a 6mm2 cable running from the wall cooker switch to the actual cooker itself. There is no cooker outlet plate to speak of.

[John Rumm]

Yes, but probably excessive... A triple socket will include a 13A fuse, so you could use 2.5mm^2 cable and know it will still be adequately overload protected. The cable will have adequate fault current protection provided by the 32A MCB at the origin of the circuit.

Yup, that would be fine.

[Tricky Dicky]

You do not say wether your original electric range was connected directly to the 45A switch or through a cable outlet. If the latter simply wire in a 4-way fused extension into the outlet, considering the low current draw this will be more than adequate.

Richard

[Stephen]

Actually, I've had a brainwave..... given that I want to keep the existing 6mm2 32A RCBO radial cooker circuit in case we ever go back to a fully electric cooker...... and maintain diversity/integrity w.r.t. to the other kitchen circuits... How does the following sound?

run 6mm2 T&E to double pole coker isolator switch above worktop.

run smoe more 6mm2 T&E from this switch to a cooker outlet thats mounted somewhere below the worktop.

I then create a mini-ring cicuit using two double sockets and 2.5mm2 T&E. I then attach the two ends of the 2.5mm T&E into the cooker outlet socket...

This would be like a 2.5mm2 ring circuit attached onto a 6mm2 32A radial cicuit.

I could then plug the gas hob, the two gas grill/ovens and the cooker extractor hood.......

So If I ever go back to a fully electric cooker, I just take off the small mini ring main and attach the cooker to the cooker outlet plate.

This way, I am not in a situation where there is a risk of up to 32A of current passing through a 2.5mm2 spur to a socket at any time.

[John Rumm]

Its not like you were in the first place given the number of sockets (i.e. one double per spur) and even then only small loads on each socket.

For all practical purposes in this case it really makes no difference if you make the final connection to the sockets by ring or a pair of spurs

- although the latter would make it a "standard" circuit - in that spurs in 2.5mm^2 are allowed (although less common) from 4 or 6mm^2 32A radials.

Keeping the cooker isolator and the outlet is probably a good idea since it allows you options and will save more work if going back to an electric cooker etc.

[Tricky Dicky]

I think you are overthinking this, to draw 32A you would need to hook up ap pliances that would draw in excess of 7kW. Somehow I do not think what you have will come anywhere near that. A 4-way extension socket protected with a 13A fuse will allow almost 3kW. Look at the specification plates on the a ppliances add up the wattage and that will give you the total this circuit will draw.

Richard

[Andy Wade]

You're over-engineering this. Given that the circuit is protected by an RCBO (presumably Type B) there'll be no problem at all in running short radial spurs in 2.5 T&E.

Also I can't see any problem with your original triple-socket idea. The loading for the clocks and ignition will be milliamps and, for the fan, an amp or two at the most. If you use the MK 3-gang socket it comes with a built-in 13 A fuse for overload protection if 'abused'. If you're paranoid you could reduce this to 5 A (say) and also change the RCBO in the CU to 16 A.

Alternatively you might want to consider whether a neater job could be done by discarding the 13 A plugs and wiring all the appliances into strategically placed fused connection units.

[Stephen]

it was more to do with ensuring its compliant to IEEE regs and also to protect against a situation of a full on short on 2.5mm2 cable on a 32A RCBO considering that 2.5mm2 cable is only rated up to 20A.

Hence my thought of creating a 2.5mm2 min ring main of 2 double sockets on the end of the cooker outlet fed by 6mm2 cable wihin the cooker's immediate vicinity to feed the two gas grill/ovens, the gas hob an dthe cooker extractor hood

[charles]

IEEE is an American body, over here was the IEE, now the IET.

The cable rating is concerned with heating - not short circuit current.

[Stephen]

I did wonder about this but my issue is lack of space for switchable FCUs between worktop and wall cupboards

basically I have along the same wall:

along the bottom:

Door no 1 | 600mm highline cupboard | 600mm gas grill/oven no 1 | 600mm gas grill/oven no 2 | 600mm highline cupboard | door no 2.

The gas hob is above the two grill/ovens inset into the worktop.

Along the top:

door no 1 | 600mm cupboard | 1200mm cooker hood & housing | 600mm cupboard | door no 2.

I want the room light switch and a double socket on the left hand side of the cooker, ( bear in mind the minimum separation distance of 300mm too....)

and then a cooker isolator switch and a double socket on the other side of the cooker area.

If I do FCU's for the hob, two grill/ovens and the extractor fan, I have to find room for 4 seperate switchable FCUs with them all being a miminum of 300mm away from the hob.

Hence my interest in having a single cooker switch feeding all four while being compliant with regs....

[Stephen]

Ok, OK, IET.... its hard keeping track of when things change like Corgi to GaSafe! :-)

7th Ed wiring regs or whatever it is called now!.....

[Tim Watts]

It's also to do with ensuring the protective device operates quickly enough (0.4s for most domestic circuits).