Electrical Near Miss - Melted 80A fuse

[autorouter]

Resistance is the enemy here, a poor blade connection or a loose screw terminal, I have found BS88 fuse holders melted together through poor connections. When using high current 50 amps a small resistance 0.01Ohms has a huge effect as power is a square of the current P= (I x I) x R
so (50x50)x0.01 = 25Watts.

This is true, it's the main factor, but there's also the plastic around the fuse metal. There's basically two kinds of plastic - thermosetting and thermoplastic. Mains plugs for example are made from thermosetting plastic, that doesn't go soft and melt when it gets hot. It stays hard, and turns brown and brittle instead. Fuse covering should be thermosetting. If it melts, as this clearly has done, then it's simply the wrong material. If there's a massive current surge, the fuse will blow in less than a second, so the plastic doesn't get chance to melt. But a long slow overload or a bit of contact resistance results in this mess.

 

[cyberyacht]

The thing with blade fuses is you can see if they are blown. How can you check midi/mega fuses?

 

[Raul]

You can see them to. Buy the ones with visible fuse.

 

[gerry mcg]

The thing with blade fuses is you can see if they are blown. How can you check midi/mega fuses?

A multimeter across the terminals set to test continuity