Why does nobody talk about how easy it is to mix up the phases on a 3-phase panel

I was wiring a new subpanel in a warehouse downtown last Tuesday and spent an hour chasing a weird hum on the motor. Turned out I had B and C swapped on the main lugs the whole time... felt like a total rookie. Has anyone else had this happen or am I just unlucky?

3 comments

3 Comments

parker1832d agoMost Upvoted

Can completely relate to that feeling man. I did the same thing last month on a compressor rack and spent a good 45 minutes scratching my head before I even thought to check the rotation. And @wendyg43 is right about those faded labels, half the time you're guessing based on which wire looks the least greasy. The worst part is how simple the fix is once you finally catch it, you feel like an absolute idiot standing there with a meter going "yep there it is." But honestly it happens to everyone, especially when you're under the gun and trying to get a motor running before the boss shows up. Just gotta learn to double check phases first before chasing ghosts.

wendyg432d ago

A wiring buddy of mine calls that move the 'phase two-step' and now I can't hear a hum without checking my shoes. Spent a good ten minutes staring at those faded labels wondering if I was colorblind or just careless. Ended up being both, because the next day I did it again on a different panel. That's when you know you need to slow down or invest in a label maker and a new pair of reading glasses.

grace_campbell2d ago

Wait you spent a whole hour on a hum and didn't check the phase rotation first? Man that is rough. I did this exact thing three months ago on a rooftop AHU and the whole unit started shaking like it wanted to tear itself apart. The worst part is walking up to the main lugs and seeing B and C swapped and realizing you just wasted half your morning. My foreman still brings it up at every safety meeting. It's so easy to do when you're rushing and the labels are all faded or covered in grease.