Fuse rating.

[Potatoman]

I need to fit a fuse in a mains plug - Its one 15 watt bulb that runs of mains - What fuse would i need?

[samz90]

You will need to use a 3 amp fuse. If it blows use a 5 amp.

[kempie]

If what blows? The fuse or the bulb?

A 15 Watt bulb should only draw a current of less than 1 Amp and so ideally a 1A fuse should be used. The bulb is itself a fuse and will blow well before the the fuse inside the plug.

[sddsddean]

Agree with kempie. It should only draw about .06 amp, so 1Amp fuse is ample.

[KebabMeister]

Can you get a 1A fuse though?  I thought there was only 3A, 5A & 13A?

[samz90]

Can you get a 1 amp fuse? Would'nt you need to use a step down transformer or something?

KEMPIE im not thick! honest! lol

I have a  Ph.D. in Biochemistry.

[kempie]

Yes, you can buy 1A and 2A fuses.

[kempie]

... should also mention 7A and 10A fuses for the sake of good order.

[Hippy]

Contrary to intuition, a fuse is not there to protect the electric device, but the house wiring. The fuse should be strong enough to pass the current for the device, but weak enough to blow should there be a short circuit that could cause the house wiring to set the house on fire! A 3 Amp fuse should be fine.

[kempie]

'a fuse is not there to protect the electric device'

If that were the case there would be no need for differently rated fuses in plugs and we could use 13A for everything.

The house wiring is protected by another fuse in the fusebox (or a circuit breaker).

[Tim Baxter]

Ok from the top Watts=Amps x Volts

The fuses are there to protect the house wiring from over heating and causing fires, in case the fuse does not blow at the device there are fuses in the fuse box, in case the fuse box fuses do not blow there is a fuse where the board's mains connects to the meter.

If a fuse does not blow and a device is malfunctioning then too much current may pass throught the house wiring causing them to overheat and cause a fire.  This is why there are fuses, back up fuses and more fuses.

So if your 15W bulb needs (15W/240W=0.625Amps <1Amp) a fuse it should be less than 1 amp, anything bigger may not blow the fuse if the lamp misbehaves.  That the bulb itself is a kind of fuse is correct BUT if the bulb holder or cable to it becomes faulty, then the bulb may not blow and the line fuse will do its job (hopefully).