Blown Fuses

[Tilly2]

Why do fuses blow on electrical appliances which have been working perfectly for three years or more? What makes the fuse blow, all of a sudden?

[Canary42]

Short circuit or overload.

[Hopkirk]

Sometimes they just blow, like filaments in light bulbs.

[Tilly2]

umm?........and that means.....?

[Tilly2]

Why would my extractor fan suddenly blow a fuse?

[AlwaysConfused]

this link gives much advice and information on fuses:
http://www.wisegeek.com/what-makes-a-fuse-blow.htm

[The Builder]

There are technical reasons, Tilly, often something that can cause a slight surge in the current that might tip the fuse over the edge. Mains voltage fluctuations, loose connections even.

Mains stability can be affected by demand on the grid for instance. If the fuse is operating near its limit, it doesn't take much. With an extractor, the consumption is pretty low, so I guess it was a surge, or the fuse has simply "worn out".

They're fairly crude devices, it doesn't take much.

[Hymie]

A fuse is placed in circuit to protect the device from the effects of excessive current flow due to short circuit, overload etc.

What many people do not appreciate is that for a fuse to operate within a relatively short period of time, over twice its rated current must flow. So if a 13A fuse is blowing within a second or so – then well over 20A will be flowing.

At 150% of rating (almost 20A for a 13A fuse) – the fuse may continue to allow the current to flow for a considerable time.

[Tilly2]

Gosh, I wish I hadn't asked now. I don't understand the answers!

[The Builder]

Haha .............. short answer then, Tilly ................

It happens :o)

[bhg481]

Bottom line. If it happens once it may just be the fuse has aged, or just one of those things. If you replace the fuse and it blows again immediately you probably have problems either with the device or the wiring leading to it.

[Old_Geezer]

Any of a number of possible reasons. Things deteriorate so the motor in your fan may have been taking a larger & larger current as time went on, and eventually the fuse couldn't cope and so evaporated (blew).

[boxtops]

It's tired, tilly

[seadogg]

You know the old story about the straw that broke the camel's back. Your poor old fuse has been asked to carry more than it can it can cope with. Its doing you a big favour 'cos it costs little to put a new fuse in than it would to replace an expensive appliance that might otherwise have been damaged.

If it happens once, just replace the fuse with one just the same. After that you may need skilled advice.

[Psybbo]

The Builder answered for me, Tilly

[Tilly2]

Ok, I'll go with 'It happens'. :-)

[BRIGHT SPARK]

Tilly.........if it happens again..dont throw the fuse in the bin...crack it open with a pair of pliers and have a look at the element wire inside. If its obliterated,your appliance has a major fault...if its just broken then its generally(but not always) down to ageing. Thats why its good practice to swap the fuses in your fridge and freezer every few years...incase they give way whilst you're in Barbados for a month.

[smartypants10101]

simple answer is nowt lasts for ever, u should be seeing it as a good safety thing than a problem, fuses blow because an electrical surge which exceeds the amp rating for the fuse which is inserted try putting 240 volts through a 12 volt dc item and then watch the sparks (don't really try this) its designed to protect you...ITS DOING WHAT IT SUPPOSE TO DO...

[beso]

The surface of fuses oxidise with age because they run at an elevated temperature even under normal loads. This effectively derates them over time.

They are a very primitive technology and are best replaced with circuit breakers if you want reliable performance.