On Friday, November 9, 2012 8:37:43 AM UTC, Doctor Drivel wrote:
"David WE Roberts" wrote in message

...



"David Robinson" wrote in message

...

Not my question, or belief, but found here...



http://forums.digitalspy.co.uk/showthread.php?t=1755197





Is there a counter-argument?





Just to note that I've just replaced the 5A fuse in an extension lead for

the second time in a week.

Rated 4A coiled and 5A uncoiled.

We use it for lights but passing builders tend to plug anything into

anything.

So yes, the fuse does protect the cable :-)



You are correct, but a little slower - it may go to 4A before the fuse

breaks. If current is say 1A and the fuse 3A, then the current increases for

whatever to 4A the fuse may not break so quick, but will eventually, so

giving protection. The fuses are designed for fault current, which means, as

one poster in the link stated a 3A and 13A will break as quick as each

other - on a fault.

really ?

A 3amp fuse will break as quick as a 13amp will iof you pass 15 amps through it I don;t think so.



I only scanned the link, but one poster I think was saying have all fuses

13A. So if he had a lamp with 0.25mm flex and 13A fuses he thinks he is

safe. OK on a lamp it is difficult to see how the current would be great

enough to melt the cable as the bulb would blow way before any current is

dangerous enough.

Unless somethijng shorts circuits the buld of course.

They only time the current would be high enough to melt

the flex would be if there is a fault, which would be momentarily and the

fuse would then snap.

After a set time depending on the curretn flowing and the lengh of time.

I "think" that is what is he on about. He says the

13A fuse will break faster on a fault than a 3A. BTW, I recall as a kid my

sister's cheap Italian (looked good though) table lamp switch melting. It

obviously had a "fault" and" a 13A fuse. A 3A fuse would have snapped

stopping the melting,

fuses don;t snap they burn out.


which was a fire hazard. The switch could be classed

as a part of the cable and the appliance the light bulb.

could be if it were on the cable.




The secret? As fuses have dropped into 3A and 13A in common use (Only

specialist outlets sell anything else these days) never install flex that is

rated less than 3A

Unless yuo need to.

and fit correct sized fuse to protect the cable. The

cable should never be rated less than the fuse.



Some fit larger rated fuses because of surge. If there is surge then fit

anti-surge fuses, not a large rated fuse.

That is not correct, you can't buy mains plug fuses in anti-surge.
Those sort are commom as internal fuses for protecting the equipment rahter than the cable.

A while ago I brought some 20mm 32ma slow-blow for a piece of euipment.