Can two ovens rated at 16A each be wired into a circuit with a dedicated circuit with a 30A fuse

Question

We are looking at installing two single ovens rated at 3.6kw each and 16A.

We currently have a double oven which is on a 30A fuse at the fusebox and is rated a max 5.1kw. A builder who will be doing some general works in the kitchen has said we need to have each oven separately wired to the fusebox and cannot use the existing cabling. Putting in new cabling would involve pulling up floorboards, new decorations, carpets etc, etc. and is simply something we do not wish to contemplate.

Is the builder correct or is there a way of using the existing cabling?

Any help appreciated - I don't intend doing the work myself but would like to know what needs to be done.

Many thanks

Answer 1

NO. Each cooker needs to be wired with 10mm csa of cable and plugged into a 32 amp mbc.

Answer 2

NO!!!!!!!!!!!!!!

Answer 3

YES; You do require a dedicated circuit for each oven.

But as has already been stated it would be the existing one with a fuse of reduced size and one new circuit.

(or buy ovens rated at 13A and whack them into Fused connection units or plug-and-socket outlets with 1.5mm flex)

Answer 4

I wouldn't do it. The ovens might take 16A each when on. That's 32 amps on a 30-amp circuit, which can cause overheating or the fuse will blow.

Also, there's probably a good starting surge when first powered on that exceeds that 16A considerably. So, if you had one on and turned the other one on, the current surge would surely blow the fuse.  

Answer 5

The builder may have said you cannot use the existing cable because it was rubber insulated, in which case the entire house may need to be re-wired.  I also note the use of the terms fuse and fuse box, which is worrying.

I note that you do not intend doing the work yourself and this answer is offered on that basis.

There is no reason why cookers need to wired directly from the main consumer unit, they usually are, because most houses have two ring mains, one or two lighting circuits, a cooker and a water heater.  What is important is that the cable supplying the cooker is adequate for the job.  This involves its current carrying capacity, condition, its length and how it is fixed.

It is either worrying that the existing arrangement is protected by a 30A fuse or hopeful, the current carrying capacity may have been de-rated to 30A because a fuse rather than an mcb was used.

6mm^2 or 10mm ^2 should have been used for a cooker circuit, regardless that the cooker currently installed is  5.1KW.  Either of these cables if correct for the original installation should easily be capable of carrying the load of your new cookers.

You do need to ascertain what cable is in situ, how insulated, condition, size, length and whether it is able to dissipate heat throughout its length.

If satisfied that the existing circuit can be used and uprated, replace the existing fuse with a 40A mcb, personally I would provide two additional MCB's in the kitchen, and uprate the existing fuse to a 40A type C mcb in the expectation that it would only blow if there was a problem with the MCB's next to the cooker.

To comment on the fact that 20A mcb's do not blow at 20A, this is true, they blow either because they are seriously overloaded, e.g. short-circuit, or because they are over-loaded and hot! they are therefore not designed to be completely idiot proof.

To add to my original response.

Heating circuits do have an in-rush current, because heating elements have a positive thermal coefficient, which is to say their resistance increases as they get hotter, thus as the thing heats up its resistance goes up, the current comes down until it achieves equilibrium.

I suggested the C curve mcb, not because of this but to provide an  element of discrimination, the type B is more sensitive and should operate first, thus if the problem is at an oven one local mcb trips, leaving the good oven in service, the C-curve mcb protects the cable to the local mcb's.

The same situation arises if you are powering an out-building at the bottom of the garden, a C-curve protects the cable, B-curve mcb's protect the sub-circuits in the shed.  Obviously if you have serious machinery in the out-building that require a C-curve or a D-curve mcb you are going to need the services of someone more serious than a part P electrician.

Answer 6

Your builder is correct to some degree - yes, you must have a separate circuit for each oven - though you would only need to run 1 new circuit as the existing one may still be used - though you would be best to derate the circuit breaker on it to a 20A - As for pulling up floorboards are you sure about that? most places I've come across will either have some form of access to either a sub floor or ceiling space...

I'd need a better description of the construction of the house but I don't

think lifting boards is necessary...

For Paul - Ovens aren't likely to have a starting surge - that's generally reserved for motors...

150 IQ (please call me for a quote ;-) ) - 10mm is serious overkill which would be an expensive waste of time - for your new oven you should get away with running a new circuit of 2.5mm twin & earth cable. 4mm t&e at the most...

Answer 7

Yes you can as long as they are in the same room and the control switch is placed within 2 metres of the ovens. as in part P of the building regs it states, where 2 staitionary cooking appliances are installed in the same room 1 switch may be used to control both appliances provided that neither appliance is more than 2 metres away from the switch. as long as the cable already installed is 4mm or 6mm it should be fine you just need to run cable from the switch to the new ovens. do not let your builder do this as its notifiable work and should be done by a part P qualified spark as a kitchen is classified as a special location, you will also require Minor works certificate after installed and tested

to add ovens rated at 13amps or less can be connected to ring circuit so you cant do that.

also a type B circuit breakers is fine, as type C and D are more for the surge on start up of electric motors.

I wish people who are not qualified lecy's would stop answering questions they know nothing about

Answer 8

In theory you shouldn't do it. But a 30 amp fuse won't actually blow until about 45 amps (it's supposed to protect a 30A circuit, not to blow at 30A), so you should get away with it.

Personally I would go for it, but make sure I didn't put the two ovens on full blast at the same time. This is known in the trade as "diversity".

BTW, at 240V, 3.6kW is actually 15A not 16A.

Answer 9

sorry but you'll have to spend the extra money and have each oven on it's own circuit. or you will spend alot af money to rebuild everything after fire

Answer 10

The amps you quoted are max amps. Rarely will and oven be at max output. but if they ever are then you will start blowing breakers.

Sorry, be smart and have a proper electrician come in and run more wire and instal an additional breaker.