The new IEC (International Electrotechnical Commission) standard, publication
947 “Low Voltage Switchgear and Control, Part 4-1: Contactors and Motor Starters,”
has been recognized by UL (Underwriters Laboratories) and is becoming
widely accepted by designers and users of motor control in the U.S. This standard
addresses coordination between the branch circuit protective device and the motor
starter. It also provides a method to measure performance of these devices if a short
circuit occurs. This standard defines two levels of component protection in the
event of a short circuit: Type 1 and Type 2 coordination.
This Product Data Bulletin describes:
_ How to conformto the new standard using motor controls built to meet
NEMA and IEC standards
_ Related benefits associated with Type 2 coordination
The IEC standard for motor starters and contactors, 947-4-1, defines two levels of
protection/coordination for the motor starter (contactor and overload relay) under
short circuit conditions. Each level of protection is achieved by using a specific
combination of motor starter and short circuit protective device.
_ Type 1 Coordination
Under short circuit conditions, the contactor or starter shall cause no danger
to persons or installation and may not be suitable for further service
without repair and replacement of parts.
_ Type 2 Coordination
Under short circuit conditions, the contactor or starter shall cause no danger
to persons or installation and shall be suitable for further use. The risk
of contact welding is recognized, in which case the manufacturer shall indicate
the measures to be taken in regards to equipment maintenance.
Faults in electrical systems are most likely to be of a low level, which are handled
well by motor controllers built to meet Type 1 coordination standards. After the
fault is cleared, the only action necessary is to reset the circuit breaker or replace
the fuses. In situations where available fault currents are high and any period of
maintenance downtime is crucial, a higher degree of coordinated protection may
be desirable.
Many industries are dependent upon the continuous operation of a critical manufacturing
process. In these conditions, it is especially important to understand that
Type 1 protection may not prevent damage to the motor starter components. In order
to ensure that high level fault or short circuit does not interrupt a critical process,
it may be prudent to consider implementation of Type 2 coordination in the
selection and application of low voltage motor controllers.
Type 2 coordination, which has no equivalent U.S. standard, does not permit damage
to the starter beyond light contactwelding, easily separated by a screwdriver or several
coil operations. Type 2 coordination does not allowreplacement of parts (except fus-
es) and requires that all parts remain in service. Beyond providing basic electrical and
fire protection, it also minimizes lost production, reduced productivity and unscheduled
disruptions resulting fromdowntime needed to replace or repair a starter.
SQUARE D Product Data Bulletin
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