Originally Posted by zzyzzx
Anyway, what I had noticed was that the existing wire gauge seemed like it was one size smaller than the fuse would indicate that it should be. I.E.- the stuff on a 15A fuse was thinner than #14 wire. The stuff on the 20A circuit was thinner than #12 wire. I have no idea why this is the case, but the load on the 15A circuit was tiny, as in I could have replaced that fuse with a 10A or even 5A fuse and it would work just fine.
Houses don't have to drive down the road--a few extra pounds here or there don't matter. Most cars aren't used for days on end, while a household circuit might have a continuous drain on it for days.
Just a guess on my part. But I think the derating for household wiring is higher than for automotive. Plus an OEM can test the exact wiring harness for days on end, in the exact chassis, for each car model--houses vary from build to build, and I don't think many people mock up household wiring all that often. A bit of conservative derating would help.
Oh--duh--not too many wire runs in a car exceed what, 15-20 feet? Not many wires in a house are that short! Forgot about that detail.
Anyway, what I had noticed was that the existing wire gauge seemed like it was one size smaller than the fuse would indicate that it should be. I.E.- the stuff on a 15A fuse was thinner than #14 wire. The stuff on the 20A circuit was thinner than #12 wire. I have no idea why this is the case, but the load on the 15A circuit was tiny, as in I could have replaced that fuse with a 10A or even 5A fuse and it would work just fine.
Houses don't have to drive down the road--a few extra pounds here or there don't matter. Most cars aren't used for days on end, while a household circuit might have a continuous drain on it for days.
Just a guess on my part. But I think the derating for household wiring is higher than for automotive. Plus an OEM can test the exact wiring harness for days on end, in the exact chassis, for each car model--houses vary from build to build, and I don't think many people mock up household wiring all that often. A bit of conservative derating would help.
Oh--duh--not too many wire runs in a car exceed what, 15-20 feet? Not many wires in a house are that short! Forgot about that detail.
Last edited:
