Electric cooker connection

[petek]

I have read previous threads on this subject but would like a specific answer to this question just for clarity.

I am preparing to fit new kitchen units in my son's small Victorian terraced (rewired a few years ago by previous owners). The existing cooker is all gas but we are fitting a gas hob/elec oven, built in cooker. There is an existing double socket outlet just above the existing worktop close and just to one side of the new cooker position.

Assuming this socket is on a ring (I haven't checked yet but I think it will be) can I fit a switched FCU as a spur from this socket and then take a flex cable from the FCU direct to the cooker? Should I fit, in addition to the FCU, a cooker switch (e.g. 45A D/P with 13A socket)? If so, should the switch be on the existing socket side of the FCU or on the cooker side IYSWIM? In fact, if I fit a cooker switch as a spur is it necessary to have an FCU as well?

In addition I need to connect a fan extractor unit. Can I take a cable from the existing socket, or from the FCU, or from the cooker switch, buried in the wall plaster to a single socket somewhere behind the wall cupboard to provide a socket outlet for the extractor?

Incidentally, I assume all this is probably prohibited by the new regs (Part P?)but where is the dividing line bewteen what a DIYer can do and what needs a pucka lecky?

TIA Petek

[Owain]

Provided (a) the socket is on the ring (b) the loading of the electric oven is Should I fit, in addition to the FCU, a cooker switch (e.g. 45A D/P

You should not fit a cooker switch *with socket* as the cooker is fully loading the spur.

You can fit a cooker switch *without* socket if you want. You may have to if the FCU is >2m from the oven or inaccessible.

You must have an FCU to limit the load on the spur to In addition I need to connect a fan extractor unit. Can I take a cable

You could take from the *fused* side of the FCU (that is crucial, as otherwise the total current from the spur could exceed 13A) to a further FCU and fuse down to 3A for the fan.

You probably cannot take two spurs from the original socket because the terminals won't take 4 x 2 mm cables.

A DIY-er can do anything. Part P does not change that.

If it is in a kitchen, however, you must EITHER submit a Building Control application to the council OR use a registered electrical contractor, not all of whom will be pukka.

Owain

(Apologies if this doesn't work -- first posting using Thunderbird.)

[Fray Bentos]

The oven should have its own supply from the consumer unit.

[Lobster]

Surely fitting a dedicated 'cooker' switch (as opposed to an ordinary DP switch) would be bad practice here: wouldn't it's presence imply that that there was a dedicated, higher-rated circuit in place for the oven, to which some future householder might think they could simply connect a

40A oven? (Not that that could ever happen in these post-Part-P days, of course!)

David

[Christian McArdle]

It wouldn't be particularly dangerous though. It would blow the 13A fuse in seconds.

Christian.

[Christian McArdle]

Your main problem here will be available diversity on the ring circuit.

Firstly, it is a kitchen, so you can forget the 100m2 business here. This is only appropriate for living and sleeping spaces, not kitchens full of high load appliances.

So,

1. Is the ring circuit dedicated to the kitchen?
2. Is it 32A?
3. What appliances are plugged into it already? Washing machine? Tumble dryer? Dishwasher? Microwave? Kettle? Toaster?

If the circuit isn't kitchen dedicated, or you have many of the appliances in (2) on this circuit, then adding an oven to the circuit will be very bad practice.

Christian.

[pknw29683]

Thanks for all your replies. I think my best and safest course of action will be:

1. Feed the cooker directly from the consumer unit to a 45A DP switch (which could also have a combined socket to use for toaster for example). There should be a spare connection in the CU as my son has just had a combi boiler installed which means that the old immersion heater has been disconnected and removed. I will check on my next visit. I presume I will have to change the circuit breaker to 45A. What size cable to run to the cooker switch?

2 Take a spur off the existing double socket via a FCU with suitable fuse for the extractor hood. I don't think it is a separate ring for the kitchen and he has a fridge/freezer, microwave, toaster and kettle plugged in. There are also the usual other household items e.g. TV & HiFi in other rooms on this downstairs ring, so I will check the total loading. What factor of safety should be used when comparing total load to the capacity of the ring? 3 What is involved in completing a Building Control form? Is it complex? Will it require a visit from someone to approve the work before/after I go ahead?

Thanks again for your excellent help. Petek (real name by the way is Peter Kay and I'm a true Lancashire lad, but unfortunately I don't own a nightclub called Phoenix Nights)

[Stefek Zaba]

A 45A breaker would need a 10mmsq cable; and TBH, cable costs are low enough that you may as well use that. The next size down is 6mmsq, and you don't want to be using that with anything bigger than a 32A breaker.

In practice, your cooker would run fine with a 32A breaker: the Regs recognise that cookers don't run flat-out for long periods, so the actual load your cooker presents over a period of minutes and upwards is noticeably lower than the figure in its manual/on its rating plate. But you should size the circuit so that the peak demand is safely met, and when you're running a new circuit there's no good reason not to use

10mmsq, which (to a first approximation) means you can avoid worrying about the route of the cable (both length and thermal insulation), higher ambient temperatures, etc etc etc. It's also entirely acceptable to wire in 10mmsq and fit the lower-rated (32A) breaker...

The necessary calculations and considerations to establish whether 6mmsq would be OK are worthwhile for an electrical engineer specifying the wiring of 200 identical Domestick Dwelling Units, where the shaving off of a few quid on each house's build costs is the name of the game, but not on a one-off d-i-y project. (One of the reasons why d-i-y often ends up being done to a *higher* standard than "professional"/commercial work...)

None of the appliances you mention are all that high a load, and don't run for long. One-ring-for-the-whole-ground-floor only starts to get marginal if the kitchen's heavy on water-heating appliances (dishwash AND washing machine AND tumble-dryer AND kettle), AND is close, in length of cable, to one end of the ring. Under those conditions, the bulk of the load is supplied by the shorter side of the ring (the current splits according to the resistance of the two paths, which is mroe or less directly related to the length of the two paths, though there's a small self-limiting effect with the resistance of the shorter leg increasing as it runs warmer). Practically, you/your son should be fine with the one ring; if it's convenient for the cooker control panel to include a socket for the kettle, that's one useful way of keeping the d/s ring load well below the 32A rating. 32A allows for a *lot* of load

- 8 glorious kilowatts...

What? who? building control? ;-) If you want reassurance, your (son's) money will be much better spent on directly getting an electrician to do a "periodic inspection report" to suss the state of the whole installation, including your planned changes, than satisfying the letter of Part Taking-the-Pee...

[Andy Wade]

Glorious kilowatts must be smaller than ordinary ones then. 230 volts times 32 amperes comes to 7.3-and-a-bit ordinary SI kilowatts - and then only if the power factor is unity.

Trouble is that 4-amps-to-the-kilowatt gets a bit optimistic for more than a couple of kW, thanks in part to our harmonised 230 volts-for-design-purposes supplies. For conservative estimation I suggest using 4.5 A per kW - well, per kVA really, but let's stop there for the moment.