[john f b]

Keep blowing fuses on a rotory knife, the allen bradley overload is not kicking off first, what could be the issue?

 

[JRaef]

Keep blowing fuses on a rotory knife, the allen bradley overload is not kicking off first, what could be the issue?

Standard thermal overload relays do not protect against short circuits, only long term current overloads. A Class 20 overload can take up to 20 seconds to trip at 600% current, but if the current jumps to 4000% in a fraction of a second, that's when you need the fuses or CB to act on it.

If this is intermittent as opposed to happening immediately every time, then it could be a failing motor lead conductor and only under certain circumstances, it makes contact with ground.

 

[sparkywannabee]

are these o/l adjustable, if so, have you checked the trip setting.