PSA: Check your torque settings before you tighten a main panel lug

Had a service call last Wednesday at a strip mall in Gary. The main breaker on a 400 amp panel was arcing bad, smelled like burnt plastic soon as I opened the door. Turns out the 4/0 aluminum feeder was only hand tight on one phase from the last guy. I torqued it to 275 in-lbs per the sticker and rechecked the other two, they were way loose too. Anyone else find loose lugs on brand new gear or is it just the older stuff?

3 comments

3 Comments

shanec611d ago

Found loose lugs on new gear more than I'd like to admit. Had a Square D panel last year, 200 amp, straight from the supply house. The main lug on one phase was barely snug, maybe 50 in-lbs. Sticker said 250. That's a fire waiting to happen. Aluminum feeders are the worst for it, they "relax" after a few heat cycles so you gotta go back and re-torque after a week or two. I always double check every lug on new installs now, even if it says "factory torqued".

violag801d ago

I had a Square D panel from the same batch @pat_roberts55 probably, and the neutral bar had a lug that was so loose it just fell off when I went to land a wire. Called the supply house and they act like I'm making it up until I sent them a pic. Thermal cycling with aluminum is real, I've started tagging every panel I install with a date to go back and recheck in a month.

pat_roberts551d ago

Man, that's the truth. @shanec61 is spot on about aluminum feeders relaxing. I had a 600 amp service upgrade last summer where I found all three phases on the main lug were barely finger tight from the factory. Used a torque wrench on everything. You'd think they'd at least give it a proper crank at the shop. What's your take on the thermal cycling thing? Do you go back and re-torque after a couple hot days, or just trust the initial tighten? Seems like nobody talks about that part but it's a real issue with aluminum.