Device coordination
The various components of a motor feeder must be coordinated. Standard
IEC 60947-4-1 defines three types of coordination depending on the operating
condition of the devices following a standardised short-circuit test.
Type-1 coordination
b No danger to life or property.
b The contactor and/or the thermal relay may be damaged.
b Repair and replacement of parts may be required prior to further service.
Type-2 coordination
b No danger to life or property.
b No damage or adjustments are allowed. The risk of contact welding is accepted as
long as they can be easily separated.
b Isolation must be maintained after the incident, the motor feeder must be suitable
for further use without repair or replacement of parts.
b A rapid inspection is sufficient before return to service.
Total coordination
b No damage and no risk of contact welding is allowed for the devices making up the
motor feeder. The motor feeder must be suitable for further use without repair or
replacement of parts.
This level is provided by integrated 1-device solutions such as Tesys U.
Contactor utilisation categories
For a given motor-feeder solution, the utilisation category determines the contactor
withstand capacity in terms of frequency of operation and endurance. Selection,
which depends on the operating conditions imposed by the application, may result in
oversizing the contactor and circuit-breaker protection. Standard IEC 60947 defines
the following contactor utilisation categories.
Contactor utilisation categories (AC current)
Contactor utilisation Type of load
categories
Control function
Typical applications
AC1
Non-inductive (cos j u 0.8)
Energising
Heating, distribution
AC2
Slip-ring motor (cos j u 0.65)
Starting
Switching off motor during running
Counter-current braking
Inching
Wiring-drawing machine
AC3
Squirrel-cage motor
(cos j = 0.45 for y 100 A)
(cos j = 0.35 for > 100 A)
Starting
Switching off motor during running
Compressors, elevators, pumps, mixers,
escalators, fans, conveyer systems, airconditioning
Starting
Switching off motor during running
Regenerative braking
Plugging
Inching
Printing machines, wire-drawing machines
AC4
Utilisation category AC3 - common coordination tables for circuit breakers
and contactors
This category covers asynchronous squirrel-cage motors that are switched off during
running, which is the most common situation (85 % of cases). The contactor makes
the starting current and switches off the rated current at a voltage approximately one
sixth of the nominal value. The current is interrupted without difficulty.
The circuit breaker-contactor coordination tables for Compact NSX are for use with
contactors in the AC3 utilisation category, in which case they ensure type-2
coordination.
Utilisation category AC4 - possible oversizing
This category covers asynchronous squirrel-cage motors capable of operating under
regenerative braking or inching (jogging) conditions
The contactor makes the starting current and can interrupt this current at a voltage
that may be equal to that of the distribution system.
These difficult conditions make it necessary to oversize the contactor and, in
general, the protective circuit breaker with respect to category AC3.
A-37