Circuit protector

Posted by Sherlock On 2018/7/13 20:47:56

Hi all,

Recently was installing a tail lamp which had a dead short owing to one of the copper strip bulb contacts being loose, twirling and touching the lamp base. I didn't notice this problem as it was under the bulb and, as the tail lamp would not light up, I was measuring voltage at the light switch block on the steering column. Soon noticed that "hot electrical" smell and looked at the dash to see the wire inside the circuit protector was lit up red hot like in a toaster (no fuse was installed). I quickly disconnected the battery and found the short.

Clearly the device protected my car's wiring. Yet I'm a bit puzzled at how this device works. The manual says the resistance wire in the protector provides enough current for some lighting when the fuse blows, but is it supposed to get red hot in protecting the circuit from the short? Maybe it gets red hot instead of the wiring leading to the short getting red hot and burning up. Even if that is so, I don't see how enough current will pass the resistor to power the lights, when all circuits including the one the short is in are drawing power through that same resistor which probably gets more resistant the hotter it gets.

Can any electrical guru out there provide the answer?