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Cooker and shower on the same circuit

Dasa

Hello everyone,

A few months back, a qualified electrician told me that a cooker and a shower can both be put on the same circuit; that doesn't sound right, surely loads using such a large amount of power must be on their own individual circuits?

I haven't been able to ask a question about this until now because I had difficulty logging into my IET account and had to get a new username and password for it.

Thank you,

Dasa

  • 0

    I get work as an electrician  because I leave electrical installations safe and useable.

    If I did not leave installations useable people would stop giving me work, even if I could “prove” that all my work complies with BS7671.

    Clearly, intelligence doesn’t mean that you are more rational or sensible.

    www.bbc.com/.../20150422-how-not-to-be-stupid

  • 0 in reply to Sparkingchip

    At the time of a related claim, your insurance company will probably decline responsibility if it gets wind that you used unqualified Bodger (cheapo) Burt from down the Hag's Head to do your electrics. (posted here just 'cos this is currently at the base of the responses).

    Z.

  • 0

    The IET ELECTRICAL INSTALLATION DESIGN GUIDE Calculations for Electricians and Designers advises in 3.1:

    ”The demand of a circuit or an installation is the current taken by the circuit or installation over a period of time, say 30 minutes”

    and references BS7671 132.3 and 311.1.

    So:

    132.3 Nature of demand

    The number and type of circuits required for lighting, heating, power, control, signalling, communications and information technology, etc shall be determined from knowledge of:

    (I) location of points of power demand

    (ii) loads to be expected on various circuits

    (iii) daily and yearly variations demand 

    (iv) any special conditions, such as harmonics 

    (v) requirements for control, signalling, communication and information technology, etc.

    (vi) anticipated future demand, if specified.

    311.1 Maximum Demand and Diversity

    For economic and reliable design of an installation within thermal limits and admissible voltage drop, the maximum demand shall be determined. In determining the maximum demand of an installation or part thereof, diversity may be taken into account.

    So given that guidance, consider this.

    Last night I pulled off the motorway and stopped at a M&S shop and bought food for our evening meal, I got home and turned on the oven then having started to cook the food I went and had a shower leaving it cooking, then I returned to finish cooking the meal whilst my wife had a shower, the main course needed to cook for 35 minutes, but I left the oven on for the melt in the middle chocolate puddings, so the oven was on for around 45 minutes plus the veg needed cooking as well.

    Therefore if we had a 6 mm circuit protected by a 40 amp MCB supplying both an electric shower and the cooker it would not comply with those regulations, in particular 132.3 (i), (ii) and (iii) because the total demand should be anticipated by the designer, also 311.1 because the thermal limits of the equipment and cable will be exceeded, quite possibly the voltage drop as well.

    Overload should be prevented by design and the circuit protection is not there to compensate for incorrect design.

  • 0

    Yesterday I went to look at some electrical work completed by someone else.

    It is a long story and there’s actually a lot to consider, but in amongst other things he has run a 2.5 mm twin and earth cable out of the shower switch to a single socket for a washing machine.

    6.0 mm shower circuit run externally clipped direct and painted B40 MCB supplying a 8.5 kW shower and a washing machine.

    Any comments?

  • 0 in reply to Sparkingchip

    I wouldn't object to to both loads intermittently running off a B40, but I would object to the 2.5mm T&E cabled being protected by a B40.

  • 0

    but I would object to the 2.5mm T&E cabled being protected by a B40.

    It might be (just) OK - it'll be protected from overload by the 13A fuse in the plug. 2.5mm² on a B40 should be OK provided Zs is low enough for instantaneous operation and PFC ≤ 6kA. The 1.5mm² c.p.c. is a bit more dubious - might be OK if PFC ≤3kA (or rather, strictly speaking, if the breaking capacity of the MCB is 3kA) or PEFC below 863A and 30mA RCD protected.

        - Andy.

  • 0 in reply to AJJewsbury

    The trouble with sockets is you can't guarantee what will be plugged into them. Stacked, unfused 2-way cube adaptors for example.

  • 0

    I should have said it’s protected by a 30 mA RCD as well as the B40 MCB.

    Further to the discussion above and the ongoing conversation it probably isn’t breaking any Wiring Regulations and the cable is rated at 47 amps, so it probably doesn’t contravene any of the Wiring Regulations and isn’t dangerous, but it’s not the way I would have done it, which is what I told the customer.

  • 0 in reply to Sparkingchip

    This is a mathematical challenge for Chris. The mathematical chances of numerous permutations.

    1. Is the shower used at full heat setting or just half max. heat setting?

    2. How often will the washing machine be using its heating element during the time that the shower is being used.

    3. How likely is it that the shower will be used at max. heat setting whilst the washing machine heater is on?

    4. And then there are the unknown factors.

    5. Which horse will win the 2.30 at Ascot?

    Z.

  • 0 in reply to wallywombat

    What about the limiting/protecting 13 Amp plug fuse?

    Z.

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