In addition to a very comprehensive thermal imaging
program to survey MCCBs and determine when a breaker
should be removed from service, the mill also effectively
employs other testing methods. Because this mill operates in
a continuous process industry, it is nearly impossible to affect
maintenance on MCCBs or other electrical system devices
during operation. This facility schedules planned maintenance
shutdowns on six-week intervals for isolated mill electrical
systems. A significant portion of MCCBs in the respective
operating area may be mechanically exercised and the trip
system tested via the push-to-trip feature on the MCCBs as a
part of the lockout and tagout procedure for equipment
maintained during the period. General condition of each circuit
breaker is noted, as external condition of the outer case may
warrant immediate replacement or a subsequent spot
thermographic inspection after the equipment is back in
service.