Cooker and shower on the same circuit

That's assuming a 10.00mm2 supply cable of course. I do not think that we have been told the details of this installation. If the existing supply cable is only 6.0mm2 there may be issues.

Z.

If the shower is rated at about 8.5kW rather than nearer 10kW, there should be no problem.

Have you ever measured a 40 degree C temperature in a domestic consumer unit Andy?

Z.

David Stone said:

Someone may shower whilst the turkey is cooking, but not for long. If they do shower for too long the MCB may trip. No problem, fully protected and safe.

So in this case we are happy to run the circuit 'hot'?

particularly in a domestic environment where electrically non-competent families with young children maybe be situated....

What can one add other than that was not how I was taught.

Good design removes the possibility of a double fault in later life.

Are people saying that no flats supplied by a 10sq.mm. submain and 60A fuse should have a cooker and a shower?

It seems that Sparkingchip is, and why is beyond me! However, it is not the first time...

Legh, this circuit will not run "hot" as you claim, please explain what you mean with a proper example.

Well. Let`s look at it this way.

I once asked about a 32A MCB running a 8.2KW (240V) shower as it would run forever OK.

The answer I was given was it is not a good idea to design for even a slight overload running the MCN on its curve.

I never once thought anything dangerous would be likely (even slightly likely) to occur but yes I will admit it`s not the best idea.

So, if everything else is as it should be, this circuit of shower and cooker combined will almost never trip in reality but it could do under the right (wrong) circumstances so we would not design it this way under most normal circumstances , would we?

If you design a circuit with a protective device the protection is there to disconnect either where there is a fault or/and overload condition.

I was under the belief that long term expected overloads in domestic appliances are not to be encouraged as ebee has stated designing a circuit where the load current exceeds the rating of the device will cause the device to disconnect, the greater the difference between the protective device rating and the full load current will shorten the length of time that the circuit stays operative. The device is now generating heat which will have a heating effect on surrounding protective devices particularly in small domestic consumer units. This term is known as running hot.

Lets take a simplistic example

A final circuit protected by a B32A MCB that is used to supply a 10kW cooker, connecting a smallish 8.5kW shower will add a 36.5 A loading to a 20A FLC including diversity for the effects of the rheostats.

The B32A breaker will disconnect in approximately 200secs with 56.5A FLC. Only a clown would attempt to reconnect the circuit as the protective device is now warm and will trip even earlier.

Now we have to consider the size of the cable conductors supplying this setup. If the circuit was designed for the cooker then the cable size is likely to be 6.0mm²; if designed for a the shower and the cooker is an add-on then the cable may be 10.0mm² but with the prevailant design attitude shown here it is more likely to be 6.0mm².

There are various installation method options here. Lets assume method C with a 6.0mm2 Best case here is 46A.

So now the cable will begin to get warm. probably not too serious if out in the open but will be a heat generator in the consumer unit.

Lets turn this around.

Some years ago I replaced a consumer unit, the existing 8.7 kW (37 amp) electric shower had been wired as spur from a socket ring circuit in 2.5 mm twin and earth protected by a B32 MCB, now admittedly the Installation Method of the 2.5 mm T&E spur was G in Free Air, there was no disputing that because it was just dangling in the airing cupboard completely unsupported, so had a current carrying capacity in excess of 27 amps, possibly even 32 amps to match the circuit protective device and the cable had not melted.

I turned the shower on and after a couple of minutes asked the young single mum who was the homeowner to touch the wire with her hand as I was doing so, she exclaimed " Bl**dy hell, I could dry my knickers on that!".

I installed a completely new circuit for that shower whilst carrying out the consumer unit, what if anything was wrong with that circuit regards non-compliances with BS7671 The wiring Regulations?

Did I rip her off by charging her to do electrical work that was not required?

Andy Betteridge. 

I have said multiple times in this thread that this is all assuming that the OCPD rating matches the cable. A 2.5mm spur off a 32A ring is under-rated unless it's only attached to a 13A FCU or one single/double socket that's assumed not to carry more than 13A. So yes, I would expect that cable to get excessively hot, and no, I wouldn't do that.