Warning: that 'quick fix' advice on a subpanel almost got me in trouble

Last month I posted asking about tapping off an existing subpanel for a new shed run. This old timer in the comments told me I was reading the code wrong and my wire sizing was off for the voltage drop over 180 feet. I brushed him off at first lol but then I actually measured the run and checked 310.15(B)(3)(a). He was dead right. I would've undersized the conductors by two gauges and probably had a fire hazard within a year. Has anyone else gotten a reality check from a forum comment that saved their bacon?

3 comments

3 Comments

nathan5452d ago

180 feet is no joke. I used to think voltage drop was something only engineers worried about, figured a few percent wouldn't matter. Then I helped a buddy wire a pump house 250 feet from his main panel. He did the math lazy like me, ran 10 gauge, and that pump ran hot and slow for a year before the motor burned out. That 40 dollar mistake taught me to always measure the actual path, not just guess. Never skimped on wire gauge after that.

evan_dixon672d ago

Hot take but I think people freak out too much about voltage drop. Yeah 180 feet is a long run but we're talking about a shed not a hospital operating room. A little voltage drop just means your tools run a tiny bit slower not that your house is going to burn down. The real danger is undersizing breakers for the load not going a gauge or two too small on wire. I've seen plenty of sheds running on undersized wire for years without any issues. Not saying the old timer was wrong but sometimes the code is overly conservative for residential stuff.

lee7332d ago

Yeah, did you at least buy that old timer a beer? I had a similar wake-up call when I was wiring my workshop. Some guy on a different forum pointed out I was using the wrong type of breaker for a GFCI circuit, said I'd be resetting it every time a motor kicked on. I ignored him for a week, then tried it and sure enough, tripped the second I plugged in my table saw. Had to swap it out for a GFCI breaker rated for motor loads, cost me an extra 40 bucks and a trip back to the store. Makes you appreciate the grumpy old dudes with the code book memorized.