Pop quiz from my lead avionics tech stumped me on wire gauge vs current limits

I followed the IPC-620 chart to the letter for a 24 AWG wire on a 7-amp load last week and the breaker kept tripping, but the old-timer says that gauge can handle it with shorter runs, so who's actually right about derating for bundle density?

2 comments

2 Comments

the_mia1mo ago

Oh man that bundle density thing got me too! I used to just grab the chart and go, figured a 24 AWG was a 24 AWG no matter what. But after watching a harness melt on a test bench because I had like 15 of them zip tied tight together I finally got it. The derating is real especially when you stack them up in a bundle, the heat has nowhere to go and that 7 amp load cooks it. Your old-timer is right about the shorter runs helping since voltage drop adds heat too but the bundle factor is what will bite you every time.

flores.tessa1mo ago

Bundle factor will bite you every time" - I see it different @the_mia. The real problem is people ignoring the ambient temp and actual circuit length, not just stuffing wires together. You can keep that bundle tight and safe if you derate upfront instead of blaming the zip ties.