Originally Posted by hebbo (Post 195461)

I was wondering whether the 3A fuse is too small for the Symtec heated grips (power connected directly to the battery through a fused relay)?

Originally Posted by Pleiades (Post 195466)

They draw a continuous ~3A in the high position, so a 3A fuse is not going to be enough. As with all resistive loads, there will be a spike in current on start up (particularly if you do so in the high setting), which could well trip a 3A fuse. If you use a fuse of the same rating as the current draw of the accessory, it will blow (eventually).

A 5A fuse would be more appropriate.

As a general rule of thumb, always select a fuse that has the next current rating up from that stated as the continuous load on the equipment it supplies.

Originally Posted by hebbo (Post 195470)

Quick question. Why has the fuse "burnt" instead of tripped straight away? Is it because the current has been slightly above 3A for some time, but not high enough to trip the fuse?

Originally Posted by Pleiades (Post 195474)

Maybe, it's difficult to say. Automotive fuses are cheap and cheerful and are not made to exacting tolerances, so they blow in different ways, no two are the same. Chances are if you could look at ten different blown 3A fuses they'd all look slightly different in the way they've gone. The burnt area you see is due to a very brief arcing across the air gap left after the fuse wire melted.