In the design of systems for buildings, different sets of performance and switching data have established themselves in relation to the various applications, both in the industrial and the residential sectors. These sets of performance data are specified in the national and international standards.
The verifications are defined to reproduce typical applications, such as motor loads (industry) or heaters (buildings). The standardized use categories set the current values that the relay or contactor must switch.
The categories AC1 and AC3 refer to data on the switching capacities that have established themselves in the industrial field. A contactor‘s duty is characterized by the utilization category together with the rated operational voltage and current indicated.
AC1 vs AC3
The difference between AC1 and AC3 contactors is that AC1 contactors are used for general purpose resistive loads but AC3 contactors are used for high inductive, squirrel cage motor switching. The rating of AC3 is lower than AC1. Because AC3 switches high inrush currents.
|General Purpose||Motor Switching|
distribution and isolation
|Starting and switching|
off running motors
By-pass and isolation for drives and soft starters
AC1 is the utilization category of non-inductive or slightly inductive loads, resistance-type electric ovens (with reference to the activation of ohmic loads). They apply to all alternating current devices with a power factor equal to 0.8.
AC3 is the utilization category of squirrel cage motors. They must have an on-off command during operation (inductive load). The main applications involve, for example, elevators, escalators, conveyor belts, bucket elevators, compressors, pumps, mixers, air conditioners, and so on. The power factor is equal to 0.45.
These switching capacities are defined in Standard EN 60 947-4-1 (Contactors and Starters – Electromechanical Contactors and Starters). The standard describes the starters and/or contactors that originally were used mainly in industrial applications.