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 the 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 article describes Type 1 and Type 2 coordination and their differences.
Type 1 coordination
In type 1 coordination, the device must not endanger persons or the installation in the event of a short circuit and does not have to be capable of continued operation without repairs or parts replacements.
Type 2 coordination
In type 2 coordination, the device must not endanger persons or the installation in the event of a short circuit and must be capable of continued use without repairs or parts replacements.
For hybrid control devices and contactors there is a risk of contact welding. The manufacturer must give maintenance instructions.
The assigned short-circuit protective device must trip in the event of a short-circuit. If a fuse is used, this has to be replaced. This is part of the normal operation of the fuse also for type 2 coordination.
Superfast semiconductor fuses must always be arranged directly in front of the power semiconductors (short cable lengths).
Benefits of Type 2 coordination
There are three key benefits of Type 2 coordination:
Type 2 coordination is intended to provide safety for operating personnel the facility and the installed equipment.
When a starter is protected from short circuits all components of the branch circuit remain intact and operational. Only fuses may need to be replaced. Savings result from a reduction in labor required to perform maintenance after a short circuit and in the number of replacement parts and required equipment. Savings are also realized by minimizing spoiled or lost production in a continuous process environment such as may occur in some food and chemical process plants.
The manufacturing process relies on continuous motor operation. If starters are damaged and must be repaired or replaced, the motors are shut down and the manufacturing process stops. By implementing Type 2 coordination, manufacturing processes should function with minimum disruption from short circuits on the motor circuits.
Difference between Type 1 and Type 2 coordination
Faults in electrical systems are most likely to be of a low level. They 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. To ensure that a high-level fault or short circuit does not interrupt a critical process it may be prudent to consider the implementation of Type 2 coordination in the selection and application of low-voltage motor controllers.