IEC Motor Protection Coordination

IEC 60947-4-1 addresses coordination between the motor circuit protective devices and the motor starters. It also provides a method to measure performance of these devices if a short-circuit occurs.

This standard defines two levels of protection/coordination for the motor 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.

  1. Type "1" co-ordination requires that, 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.

    Usage: Low fault level systems.

  2. Type "2" co-ordination requires that, 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 as regards the maintenance of the equipment.

    Usage: High fault level systems.

An ABB online application is available to help select motor circuit protection, contactor and overload relay combination.Below is an example:

  • Protection Device: MCCB
  • Rated Voltage: 400VAC
  • Short Circuit Current: 10kA
  • Starter: DOL - Normal Start
  • Coordination Type: IEC Type 2
  • Overload Relay: TOL
  • Motor Rated Power: 18.5 kW
  • Selection

3254 = 3245 = 3238

About the Author

Ver Pangonilo
A Filipino Engineer, Registered Professional Engineer of Queensland (RPEQ) - Australia and Professional Electrical Engineer (PEE) - Philippines with extensive experience in concept select, front-end engineering, HV & LV detail design, construction and commissioning of Hazardous and Non-Hazardous Area electrical installations in water and waste water pipeline and pumping facilities, offshore platforms, hydrocarbon process plants and pipelines including related facilities. Hazardous area classification and design certification (UEENEEM015B, UEENEEM016B, UEENEEM017B).
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