plug fuse, for a microwave, 3amp or 13amp?

[alacaz]

Can anyone tell me what fuse i need to use, 3amp keeps going when i turn the microwave on? thanks

[tigga]

mine is a 750 watt class D and is fitted with a 13 amp, hope this helps.

[Buenchico]

Assuming it's a normal domestic microwave oven (i.e. somewhere between 600W and 850W,) electrical theory suggests that a 5 Amp fuse is what is required. In practice, most electricians (and manufacturers) fit 13 Amp fuses as they recognise that any fault which is likely to blow a 5 Amp fuse will also blow a 13 Amp one. Either way, a 3 Amp fuse is definitely too low a rating.

Chris

[mibn2cweus]

What is your mains (AC) voltage?

[stanleyman]

The fuse is there to protect the cable to the appliance and any low current switches such as in central heating programmers. You can use a 10 or 13 amp fuse for a microwave and as a general guide for fused plugs the smaller fuse sizes should be plus around 50% of the normal load to prevent overheating and premature failure. The important thing is that the circuit cannot be allowed to overload and at the same time the fuse is not too small to overheat in normal use.

[alacaz]

Many Thanks to you all for such a fast responce, I can now eat again and sleep in peace afterwards!!

Alacaz

[gen2]

Many appliances when switched on take a higher current than their normal working/running current. This is true particularly for appliances containing motors and explains why a fuse might blow even if it is greater than the calculated load current.. Most microwaves have motors to drive the turntable. I don't know if the microwave generator also takes a higher startup current. In these cases you cannot apply the standard W = A V formula to arrive at a suitable fuse rating. Instead look at the cable fitted to the appliance, A thick cable indicates you should use a 13A fuse. A medium cable indicates a 5 A fuse, and a thin twisted (or untwisted) pair (such as found on a table-lamp or phone charger) only requires a 3 A fuse.

[tony1941]

Yes, gen2, all of this is true; however, the type of fuse fitted in a standard UK plug is very tolerant of short term overloads. The real problem is that a 750W microwave delivers 750W of power into the food. To do this, it has to convert the mains lead supplied energy into RF power and there is a loss implied in this (otherwise the components of the microwave and the casing would not get warm (as mentioned elswhere on AB last week)). The real figure for the load might be on a plate at the back, but it will certainly be much higher than the 750 - 900 sort of figure. A 13A fuse is quite appropriate, but 10A will probably work for a normal domestic unit. (Hint - commercial 1800W microwaves will run on a 13A fuse, but there is not much headspace!)

[Gibboman]

There are many different fuse sizes, but as a rough guide we normally use a 5 amp Fuse for anything up to 700 watt and 13 for anything over. (230ac)

[pjsimm]

the only fuse ratings that are recognised by the iee electrical regulation which is law within Britain are 3amp or 13amp so if your appliance is 750watt or below it should be fitted with a 3amp fuse anything above should be fitted with a 13amp fuse