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
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?
Aim to work one hour less this week than last week and get paid the same.
"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
| 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.
Valid options include:
1. Ignore old cooker circuit and plug into a socket on a ring circuit
(subject to consideration of likely load on said circuit from other
2. Wire directly to cooker connection unit. Change relevant fuse or
MCB in consumer unit to 16A to protect appliance flex.
3. Change cooker connection unit to unswitched 13A socket or fused
connection unit, and plug-in or connect oven. Fit 13A fuse in plug
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
32A radial circuit.
Thanks for you reply Andy.
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).
b) The socket can't be switched off by accident.
c) An unswitched socket is cheaper :)
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
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.
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
- 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
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.
HTH - Stefek
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