mikeames
Senior Member
- Location
- Gaithersburg MD
- Occupation
- Teacher - Master Electrician - 2017 NEC
Teaching a course and stopped to think about the above references. Basically reducing washers do not require a bonding jumper, but ringed knockouts do. The idea is 277/480 produces 5x the heat. Ok I get it, but... In real life I have seen boxes where the ringed knockouts are barely punched to where you almost bend the box removing one step or ring. On the contrary its hard to get reducing washers tight, no less conductive on top of the paint that a load center may have on it.
Scraping the paint off the cabinet when using a reducing washer is required. My point is I feel a locknut properly tightened on a concentric knockout in a painted load center will make a better connection than the same connection made with a reducing washer. I suppose I am wrong since those small points where the locknut cuts in are too small for a 277/480 fault? That cant be the reasoning though because no bonding jumper is required on Non-concentric knock outs.
So with this logic the weakness is in the connection of the concentric tabs in the knockout. So is the concentric knockout less conductive or capable of a fault than a reducing washer sitting on top of scraped steel?
Scraping the paint off the cabinet when using a reducing washer is required. My point is I feel a locknut properly tightened on a concentric knockout in a painted load center will make a better connection than the same connection made with a reducing washer. I suppose I am wrong since those small points where the locknut cuts in are too small for a 277/480 fault? That cant be the reasoning though because no bonding jumper is required on Non-concentric knock outs.
So with this logic the weakness is in the connection of the concentric tabs in the knockout. So is the concentric knockout less conductive or capable of a fault than a reducing washer sitting on top of scraped steel?
