Cooker and shower on the same circuit

well 'can' and 'its a good idea' are not the same.
The regs do not exactly say 'never connect a shower and a cooker to the same circuit' I presume the assumption is that anyone wanting to do something that odd would have a really good reason.

Now I assume this is the sort of shower that heats the water - not just an electric pump from a hot water tank heated another way - that would be OK, if eccentric, as the pump is a very light load compared to a heating element, though then I;d expect a local fuse for the motor.

The regulations do strongly suggest that large loads like water heaters, cookers, and instant showers should have a dedicated supply and that it be sized for the load.... (well yes they would, normally, we expect that)

Now maybe, if you know for certain that the two will never be switched on  together, it could be made to work, but even in a small 1 bed flat there is the risk of someone having a guest for dinner or something and getting a shower at the same time. In a large household it is very likely.

It may be safe in some circumstances, I suggest it is never a good choice - perhaps as a temporary fix while building work is done or something, but only when everyone involved understands the limitations.

Mike.

It depends upon the power of the shower and the cooker!

Let's say 9 kW shower plus 4 kW cooker. That's 13 kW or 56 A. That would require a 63 A MCB and 16 mm² T&E.

That leaves two potential problems:

(1) If you down size the cable at the branching point, you will need overload protection there (433.2.1); or

(2) If you stay with your 16 mm² T&E, will it fit the terminals?

Much better to have separate circuits.

I am not aware of any regulation that says "you can not do that" But as has already been said it is a very odd way to proceed and poor practice.

If the circuit is sized for the cooker OR the shower, then sooner or later both will be used and trip the MCB.

If sized for cooker AND shower then see earlier remarks about large cables and terminal sizes. An MCB big enough for cooker AND shower might not fit a standard consumer unit and probably wont discriminate with the cut out fuse.

I have installed a single circuit for a cooker and a shower, but only as a temporary measure for my own use in a single person  flat.

I have also used a single circuit to supply the cooker OR the shower via a changeover switch, useful when only a limited supply is available.

Have even installed a three way changeover in a place with only about 32 amps available.

One 3 amp circuit for lighting

One 3 amp circuit for 13 amp sockets for only low loading appliances.

One 32 amp circuit to supply the cooker, or the shower, or the other socket circuit used for heaters, water heaters, and other heavy loads. All a bit of a bodge, but needed as LPG that was used for heating and cooking became hard to obtain.

A long time ago the regulations did have a stipulation to the effect that circuits rated above 15A could only serve a single 'point', but that was a very long time ago - pre ring circuits, but these things often persist in background memory and attitudes long after they've been dropped from the regs.

Sometimes two large power items on the same circuit can make sense. A few years ago there was a short lived fashion for body dryers - basically a 9kW fan heater built into the ceiling to dry people off after a shower - they'd often be wired into the shower circuit on the basis that if someone was getting dried they couldn't be in the shower at the same time. Likewise some people have have more than one shower in a house - but for reasons of locational convenience rather than any need to use two simultaneously. You can get automatic "priority" switches to handle situations like that and ensure nothing gets overloaded.

  - Andy.

The body driers had an automatic changeover in it, so the shower could not be used at the same time, I tried one out in the training room at Triton showers, fully dressed of course then did not see another one for over ten years.

Hardly a popular appliance.

Someone will be along shortly to tell you it doesn’t contravene the regs, it is of course not possible to use both appliances at the same time and the circuit needs to be protected against overload, so you cannot assume it will be okay to connect a cooker to an existing shower circuit,  because an existing shower circuit  may not be protected against overload, 

I would be tempted to state that this setup is beyond the remit of a modern day level 3 electrician as it is a non-standard circuit arrangement being out of the scope of the OSG. Perhaps perfectly acceptable as a lash-up in labs, caravans, or the production of neferious substances in squats but not suitable in domestic 2 up 2 down terraced sized installations.

As long as the OCPD is suitably rated to protect the cables, then I don't see any safety issue. If the shower and cooker overlap for a bit, the cable will get a bit warm. It's unlikely the cooker will be on full power for any long length of time - otherwise the kitchen would start getting unbearably hot. In unusual situations where there is a long overload, the OCPD will eventually trip. This is inconvenient but not dangerous.

Well. If its on a "priority switch" type circuit then ok but it is difficult to imagine the arrangement requiring two such items on the same circuit if it is not for your own temporary use only

The regs do not exactly say 'never connect a shower and a cooker to the same circuit'

and

I am not aware of any regulation that says "you can not do that" But as has already been said it is a very odd way to proceed and poor practice.

and

A long time ago the regulations did have a stipulation to the effect that circuits rated above 15A could only serve a single 'point', but that was a very long time ago

and

As long as the OCPD is suitably rated to protect the cables, then I don't see any safety issue. If the shower and cooker overlap for a bit, the cable will get a bit warm. It's unlikely the cooker will be on full power for any long length of time - otherwise the kitchen would start getting unbearably hot. In unusual situations where there is a long overload, the OCPD will eventually trip. This is inconvenient but not dangerous.

good grief !

Oh come on, this is not standard practice for level 3 journeyman electricians doing work in domestic installations being used by non-competent persons is it?.

Please do not justify imaginative electrical solutions that are perfectly acceptable on an establishment under the direct control and supervison by a competent electrical engineer with basic standard domestic installations likely to generate ambiguity, confussion and eroneous solutions for others who will be obliged to provide the maintenance.