The IEEE has also published a standard for maintenance of
MCCBs titled Recommended Practice for the Selection, Field
Testing, and Life Expectancy of Molded Case Circuit Breakers
for Industrial Applications [10]. The work was originally
sponsored by members of the IEEE Petroleum and Chemical
Industry Committee after the group discovered a need to raise
the general level of understanding for specifiers and users of
UL 489 molded case circuit breakers. Included in this newer
2005 standard is an important section titled ‘Procedures for
field testing and determining the remaining life of molded case
circuit breakers’. The standard establishes specific methods to
ascertain when a MCCB should be removed from service,
including photos of MCCBs with visible wear or damage to the
molded case frame as shown in Fig. 4. There is also an article
in the standard addressing methods for an exposed face and
lug temperature check using an infrared non-contact
temperature measuring instrument. In this section,
temperatures detected above 54.4oC (130oF) on the exposed
insulated face of the breaker, or the adjacent surrounding
dead front surfaces of the enclosure, warns that a reason for
the elevated temperature must be found before returning the
MCCB to service. An explanation suggests that the most likely
cause of elevated temperature is a loose connection. A host
of additional field tests such as Individual Pole Resistance
Test and Instantaneous Overcurrent Trip Test are clearly
defined with step-by-step procedures. Most tests require