combi microwave problems

31 Mar 2009
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United Kingdom
Apologies for asking this because i should be asking my electrician, but i can't get hold of him for love nor money. Would really appreciate any thoughts or advice....

I've had a new kitchen fitted which includes a fitted combi microwave next to a gas oven (they are in side by side units). I had the electrician come and do all the elecs from scratch as it was an extension but i'm currently unsure as to whether the supply i have for the combi microwave is appropriate.

Basically, the microwave is acting up and the retailer i bought it from says that it sounds like it's a power issue and that it needs a 30amp feed.

There are basically two double sockets at the back of the microwave, (each of which has an isolation switch too). The oven is plugged into one of these double sockets and the electricians obviously intended to have the microwave plug into the other.

My specific question i guess would be, is the oven supply not 30A anyway? And therefore shouldn't the microwave work perfectly if plugged into the double socket that the oven is in?

If both sockets are 13A, how do they get changed to 30A - the wire needs changing yes?

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sorry, i'm an idiot, it isn't a gas oven, it's electric. I've been so preocupied with my gas hob today that i've managed to convince myself the the oven is likewise.....
If the microwave really does need a 30A supply, it should NOT be plugged into any socket. It should be wired to it's own separate circuit.

What make and model is the microwave?

When you say the microwave is 'acting up', what exactly is the problem?
You're getting in a muddle here.

What WATTAGE is the oven?

What WATTAGE is the microwave (INPUT power)?

A standard socket is usually on a 30 amp circuit, but the socket is called a 13 amp socket, because this is the maximum it can provide. The circuit can handle 30 amps.

Anything over 13 amps MUST be on its own circuit.
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I think the retailer is bullshitting you there mate.

I also think you're a little confused. Generally speaking, ovens and microwaves can go on a 13A plug. If it was needing a bigger supply it would simply blow its fuse - not 'play up'.
Thanks everyone. I'm somewhat more confused now and am digging out the installation instructions.

Meanwhile... the symptoms are that the microwave fails to warm things up, turntable turns jerkily, stops humming as if to suggest it isn't cooking.

My layman understanding of it is that because it's a combi microwave, it uses more power for the oven part of it, than it would if it was just a microwave - it's a smeg S45MCX

Nominal power: 3.40 kW
Grill power: 1.50 kW
Microwave output power: 1.00 kW
30 Amp power supply required

So it should be hard wired? Is there any way i can tell by looking at the cable that runs to the socket if it is correct?
I should also add though that a smeg engineer did come out for a separate issue for which he had to take out the microwave, and he didn't comment on the fact that he had to unplug it and that it wasn't hard wired... perhaps suggesting that this is an ok whay to do it?
There's your problem right there.

3.4KW = 14.78amps at 230volts so you cannot put a 13A plug on there.

It will either have to share the supply for the oven, or you'll need to put it on its own supply.

What do the MI's say re connection?
Ok. So 2 points -

1) i understand now that a 13A plug is not suitable - but how do i know that i have a 13A plug on it? Maybe it is a higher ampage? Or are we talking plug sockets?

2) how do i know that the oven supply is correct for the microwave? and how do i connect the microwave to the supply for the oven? I can't just plug it in?

Sorry for my confusion!

Instructions refer to "if using a plug", so it's seems to be ok with them
The instructions about using a plug probably refer to use in European countries where 16A circuits are common. This does not apply in the UK.

The most likely installation is to have the oven permanently wired to either it's own circuit, or to the cooker circuit (which is probably 32A).

The erratic behaviour of the microwave suggests either there is a loose connection somewhere, or there is a fault with the microwave itself.
If there is a loose connection, this will be made worse every time the microwave is used.
so if i plug it into the same socket as the oven it should work if the problem is indeed due to the circuit not being correct?

i need to check though - is there any chance whatsoever that the oven would not be on a higher Ampage and that i would just be swapping onto a circuit which is exactly the same?

Basically, i just want to make sure that i have definitely tried this microwave on a suitable circuit, so that i can rightfully complain, rather than looking like a fool when it turns out that it just wasnt installed properly.

fyi, the information is specifically for the uk, so there shouldn't be that issue with the plug
Listen, UK FUSED THIRTEEN AMP PLUGS are called THIRTEEN AMP PLUGS for a reason - this is their MAXIMUM rating.

You CANNOT connect anything over thirteen amps to a thirteen amp plug.

A thirteen amp socket can be on a circuit rated at 16, 20, 32 or 40 amps, but it can ONLY supply THIRTEEN AMPS.

Please stop asking :LOL:
There are two issues here
1) your microwave is connected to a 13A plug when it (potentially) needs more
2) your microwave is not working properly, due to it being buggered, OR a loose connection
The two problems are NOT related.
So cutting to the chase, i don't need to understand this, but i do need to work out if this machine is faulty. How do i do that?

And i know that it SHOULD be hard-wired and it SHOULD be on it's own circuit and that that is the easy answer. but i am a total electricity layman and i need to work with what i've got which is a questionable microwave, a working oven and two separate circuits.

Out of interest here, is a point being made that plugs are only ever 13amp and can't go any higher? Is that why i seem so stupid?

Out of interest here, is a point being made that plugs are only ever 13amp and can't go any higher? Is that why i seem so stupid?

Yes. :LOL:

If you have a 32A circuit for the oven and micro, just connect the micro straight to it. (unless the MI specify anything else)


Get a decent local spark in and he'll check all the connections, then connect it up properly. Then you can go back to the retailer and tell them you want a new micro :cool:

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