Cooker and shower on the same circuit

I'm afraid I agree with Wally above. It is perfectly true (unfortunately) that this may not be understood by many "electricians", but that is because they are not suitably qualified for the job. The only point could be that the "manufacturers instructions" state a final circuit CPD, but this can be installed at any convenient point at the connection to the circuit, making the large supply simply a sub-main. In fact it may be a very convenient way to prevent mahem trying to install a new circuit , when the arrangement will make installation easy. Cable "overload" is perfectly safely handled by the CPD in the CU, and load diversity takes care of the rest. Tripping is very unlikely and should it ever happen, so what? Just reset and stop showering. Neither appliance can take excessive current due to any conceivable fault, so why are we even having this discussion? "Standard Practice" is a poor excuse for failure to understand the most basic part of circuit design! Also this priority switch idea is daft too, exactly why?

wallywombat  David Stone 

How long to cook a turkey

For a standard turkey that's around 6kg/13lb, the cooking time will be around 4 hours.

Roast timer - BBC Good Food

Yes, but once the oven has reached temperature, it switches off, just occasionally switching back on to top up the temperature - rather than continuously pumping out 3kW or whatever for 4 hours. Hence my comment about the kitchen otherwise becoming unbearably hot.

Okay, we can apply diversity for the cooker, what about the shower?

B ut what if it was a 1 bedroom flat? You would be unlikely to use the cooker while you're in the shower. Just a thought.

Regards, burn

“B ut what if it was a 1 bedroom flat? You would be unlikely to use the cooker while you're in the shower. Just a thought.”

Could me old fashioned, I always did and do shower before a date night.

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. You seem to be suggesting something a bit strange Andy, because sub-mains often have more potential loads than the supply, including your house from the DNO I suspect. Mine certainly does, but if I happen to pop the cutout fuse (I don't) is this dangerous or a disaster? As I keep saying, diversity is about time as well as load. Assuming we have a 10mm cable and a 63A breaker, how long can we run at 65A before the cable melts? That is 45A for the shower and 20A for the cooker average BTW, Even worst case the cable temperature will only reach about 71C (Table 4D5A), This is very unlikely however, because this will take about an hour at least, and require a 30C ambient. Lovely Christmas here in Australia!

Too many assumptions are being made to try and argue it’s not an issue:

1. 10 mm circuit.
2. Cooker not used for for anything other than warming ready meals.
3. Shower only used briefly.
4. Cooker and shower not used at the same time.

As a working electrician who has years of repairing existing electrical installations, including after electrical fires I can tell you that assuming such things can result in a Big Bang and a fire, the bang is not an issue, the fire can be a  major issue.

Why would there be a fire? I'm  not making any assumptions other than that the OCPD rating matches the cable. This is no different than someone plugging multiple electric heaters onto a single ring circuit. The MCB trips quickly with many heaters, or slowly with a few heaters. In neither case is the fixed cabling damaged, nor does the house burn down.

Agreed its not an ideal arrangement (the house owner may get annoyed by the shower circuit occasionally tripping) but it's not dangerous.

Have you never turned up at a job to find a fused switch, fuse board or consumer unit has caught fire?

I went to a job a few years ago to find that the entire external meter box had gone along with the cut out, meter and consumers fused switch. What caused the issue was never identified to the home owner, the 999 call resulted in two fire engines and their crews, two police cars and several officers, an ambulance and crew, Central Networks and Metering Services attending, because it was a barn conversion and it was anticipated that a major incident may develop.

Incidents such as this does make you realise that a fuse is not the be all and end all of electrical safety, that had two fuses in it the DNO and the consumers, neither prevented a fire.