over-rated fuse

[sdavies21216]

Hi Guys, sorry I wasn't sure where to post this...

I have just found in the garage an old tape deck (cassette), I thought "I'm never going to use that again", but I thought I may as well keep the plug as u never know. I took off the plug top, and found a 13amp fuse inside!! Until a couple of years ago I was using it with an over-rated fuse!! Now I must stress, it has now gone in the bin (together with the plug as it was pretty grotty after all that.) Anyway, it made me think how lucky I was that something didn't go wrong with it, there could've possibly been a fire, depending upon the current-carrying capacity of the cable I suppose. Anyway, I've gone on far too much, I do apologise!!!

Stuart

 

[333rocky333]

It may have been fused down within the appliance anyway.

Sometimes the plug fuse only really protects the mains lead.

If it is really old and the plug pins are not sleeved, you should destroy and bin the plug also.

 

[TicklyT]

Some small appliances need a plug top fuse of much greater rating than their power consumption suggests. If they have switch mode power supplies or toroidal transformers built into them, these can draw many times their normal running current for a fraction of a second when they are first turned on. This can be enough to pop a plug top fuse.

The internal fuses in the appliances may have a much lower value, but often have a time delay built into the fuse, so the power up surge doesn't blow them.

As plug top fuses have no time delay, and are made in a limited range of values, the fuse selection is a compromise. It needs to be low enough to protect the appliance lead, but high enough to survive the surge current.

Why are 5, 7 and 10 Amp fuses so rarely available? One little 50 Watt power supply I often encounter has a tendency to pop it's 5 amp plug top fuse occasionally.
As the most commonly available fuses are 3 or 13 Amp, they are often found with a 13 Amp fuse protecting a 0.5 sq. mm mains flex with a 'figure of 8' plug on the end