Debate: Should you trust the 'torque to yield' rule on panel lugs or just crank them?

My journeyman buddy swore I was overthinking it when I used a torque wrench on 200A service lugs at a house in Oakwood last Tuesday. He said just snug them up good and call it done, that's how he's done it for 15 years. But I followed the spec sheet anyway (you know, the one that says 275 inch-pounds) and one of the screws actually bottomed out weird before hitting torque. Now I'm wondering if he's right that the aluminum bushing can compress too much if you follow the book exactly. Has anyone else run into a situation where the manufacturer's torque spec seemed way off compared to what actually works in the field?

2 comments

2 Comments

anderson.gavin5d ago

Bet the issue was thermal expansion rates differ between aluminum and steel when loaded up hot.

robinson.leo4d ago

Honestly I was reading about this the other day on some engineering forum. They were saying the aluminum heads expand way faster than the steel block and that's where the gasket failures usually start.