Thursday, February 20, 2014

Understanding Type 2 Coordinated Protection in Motor Branch Circuits

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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