I have just taken delivery of a Rangemaster P90 (all gas model) cooker. This has gas rings, gas grill, one gas oven and one electric oven rated 2.5kw. The electrical flex on the cooker comes fitted with a 13amp plug so I assume this is correctly rated for the oven and the cooker's other electrical functions.
The plug has thrown me as I was expecting to simply connect it to the existing 45amp cooker connection unit. So can I simply remove the plug and wire it into the connection unit or do I have to change the connection unit for a 13amp socket?
"Bill Gardener" wrote | Rangemaster P90 (all gas model) ... one electric oven rated 2.5kw. | The electrical flex on the cooker comes fitted with a 13amp plug | The plug has thrown me as I was expecting to simply connect it to the | existing 45amp cooker connection unit. So can I simply remove the plug and | wire it into the connection unit or do I have to change the connection unit | for a 13amp socket?
I would change the cable outlet plate to a socket (retaining the cooker control unit (switch)). That way the cooker flex receives 13A fuse protection rather than being dependent on the 45A MCB.
Label the socket as '45A cooker supply' though for future reference.
Ignore old cooker circuit and plug into a socket on a ring circuit (subject to consideration of likely load on said circuit from other kitchen/utility appliances).
Wire directly to cooker connection unit. Change relevant fuse or MCB in consumer unit to 16A to protect appliance flex.
Change cooker connection unit to unswitched 13A socket or fused connection unit, and plug-in or connect oven. Fit 13A fuse in plug or FCU.
In options 2 & 3 retain the existing cooker control switch (within 2m of new appliance) to provide control & isolation.
My own preference would be option 3. Option 1 is not ideal if the other sockets are RCD protected. The old cooker cct could also be used to feed other sockets or fixed appliances if desired, by converting it to a standard
As it's been shipped with a 13A plug, the appliance flex and internal wiring have probably been designed in the belief that there will be a
13A overcurrent protection provided by the plug-top fuse (or a 16A radial MCB if the same cooker is marketed in Europe). So to be sure you're staying within the design setup, you would fuse down to 13A somewhere. All of the following would be OK from the strict point of view of this cooker: - forget the cooker connection unit and plug the cooker in to an existing socket on the kitchen ring; - replace the existing cooker connection unit control panel with one which has a 13A socket built-in, and plug your cooker in to that; - replace the existing cooker connection unit with a single or double 13A socket, plug cooker in there; - replace cooker conn unit with a dual box mounting two single accessories side-by-side, with a fused connection unit for hardwiring the cooker and a handy 13A socket for a kettle/toaster/whatever; - hardwire into the existing cooker connection unit and replace the 30A/40A MCB currently supplying the circuit with a 16A jobbie. (DIN-rail mount MCBs cost 5-6 quid a throw).
These have various tradeoffs among work you have to do, versus keeping the kitchen appliances working off multiple circuits (generally a Good Thing).
Now, in point of fact, it *might* be OK to wire into the existing cooker unit anyway, leaving its 30A/40A protection device in place. Since you have a fixed appliance here, "nature of the load" arguments say it can't give rise to an overload which would heat up the cooker's flex and internal wiring - there's no foreseeable fault which would make the cooker's overn element mysteriously pull, say, 6kW for minutes on end. So the job of the overcurrent device in this circuit is to provide only *short-circuit* protection, rather than overload protection as well. And to work out whether the existing 30A or 40A fuse/MCB provides adequate short-circuit protection, you'd need to look up (in the Tables) the resistance of the length of cooker flex, work out how much current would therefore flow in the event of a short to earth and a short to neutral, and check (a) that enough current will flow to cause the protective device currently in place to disconnect within the required time (0.4s is what I'd use as the Soon Enough criterion: can't remember if you could get away with the laxer 5s figure for this circuit, but for personal safety I'd want my cooker to EEBADS within 0.4s ;-); and (b) that during the disconnecting period, the temperature of the flex won't rise above the relevant figure (maybe 90degsC, maybe 110, all depends on its insulation type). With a noral-length flex (2m, say) you might well find you're OK.
But you shouldn't just guess. The point is, the cooker manufacturer has already *done* these calculations for the case of a 13A cartridge fuse as the short-circuit protection element, and has specified the flex and internal wiring accordingly. So the way to leech off that design effort is to arrange for your shiny new cooker's electricity supply to have a
13A fuse in it somewhere along the line, which all the previously-listed alternatives provide. So I'd recommend one of those rather than the less-certain route of wiring right in to the heftier cooker control panel as-is. If you want to preserve resale value and give minimum scope for eyebrow-raising on resale, the "put in a cooker control panel with an integral 13A socket" gives future purchasers the full flexibility of a gas or all-electric cooker, while giving you a place to plug in the mixed-fuel cooker you just bought.
I like your option 3, but why unswitched 13A socket, why not switched?
Also my cooker cable goes first to a big red switch and then from there to the cooker connection unit. I would still like this big red switch in, will this be OK then?
a) The cooker should be completely isolated for servicing - A switched socket only provides disconnection of the Live. An unswitched socket removes the possiblity of someone just switching off at the socket - They will have to unplug the cooker or switch it of using the cooker control switch (ie the big red one).
I know. I'm going for the Classic 90, which has the same arrangement. My suspicion is that the very tall and thin second oven can't be heated evenly unless it is fan assisted, which is easier with an electric element than a gas burner.
I want the "gas" model instead of dual fuel, as I hate electric grills, which seem designed to emit smoke. Any fat spitting in a gas grill is simply used as fuel. I probably prefer gas ovens, too, as they seem to heat up much quicker than electric.
If the cooker switch is a one gang switch then this could be replaced for a
13A FCU and the cooker can then be hardwired into the CCU. This would " retain the existing cooker control switch (within 2m of new appliance) to provide control & isolation."
Otherwise change the CCU for a single socket (Andy's option 3). Which is the easiest, cheapest and fastest option and electrically fine.
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