B. NEMA Standard AB4
In an effort to better frame the ongoing maintenance
recommendations for MCCBs after they have been installed
and are operational, the National Electrical Manufacturers
Association (NEMA) first published the AB-4 Standard [9] in
1991. This document is available as a free download at
http://www.nema.org/. The document focuses on inspection,
preventive maintenance, and test procedures for breakers that
are in service. One area of maintenance focus in this
document is a recommendation to mechanically cycle MCCBs
periodically. In addition, when the breaker includes a push-totrip
actuator, the tripping mechanism can also be tested. This
test exercises the trip mechanism components called upon to
function during the interruption of a fault. In most MCCB
designs, initiating a test-to-trip results in the breaker handle
toggling to the center position. In order to reset the trip, the
MCCB handle must be moved to the off position before the
breaker can be re-energized.
B. NEMA Standard AB4
In an effort to better frame the ongoing maintenance
recommendations for MCCBs after they have been installed
and are operational, the National Electrical Manufacturers
Association (NEMA) first published the AB-4 Standard [9] in
1991. This document is available as a free download at
http://www.nema.org/. The document focuses on inspection,
preventive maintenance, and test procedures for breakers that
are in service. One area of maintenance focus in this
document is a recommendation to mechanically cycle MCCBs
periodically. In addition, when the breaker includes a push-totrip
actuator, the tripping mechanism can also be tested. This
test exercises the trip mechanism components called upon to
function during the interruption of a fault. In most MCCB
designs, initiating a test-to-trip results in the breaker handle
toggling to the center position. In order to reset the trip, the
MCCB handle must be moved to the off position before the
breaker can be re-energized.
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