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Contact load classifications
Contact load classifications (related to the utilization categories defined in EN60947-4-1 and EN60947-5-1)

Utilization categories indicate the type of electrical load and duty cycle of the loads to ease selection of contactors and relays.


Fig.1 : Contact load classification example


Load classification  Supply type  Application  Switching with relay
AC1
AC single-phase 
AC three-phase 
Resistive or slightly Inductive AC loads. Work within the relay data.
AC3
AC single-phase 
AC three-phase
Starting and stopping AC three-phase of Squirrel cage motors.
Reversing direction of rotation only after motor has stopped rotating.
Three-phase:
Motor reversal is only permitted if there is a guaranteed break of 50ms between energisation in one direction and energisation in the other.
Single-phase:
Provision of 300ms “dead break” time when neither relay contacts are closed - during which time the capacitor discharges harmlessly through the motor windings.
For single-phase:
Keep to the relay data.
For three-phase:
See “Three-phase motors” section.
AC4 AC three-phase Starting, Stopping and Reversing direction of rotation of Squirrel cage motors. Jogging (Inching). Regenerative braking (Plugging). Not possible using relays. Since, when reversing a phase connection, severe contact arcing will occur.
 
AC14 AC single-phase Control of small electromagnetic loads (<72 VA), power contactors, magnetic solenoid valves, and electromagnets. Assume a peak inrush current of approx. 6-times rated current, and keep this within the specified “Maximum peak current” for the relay.
AC15 AC single-phase Control of small electromagnetic loads (>72 VA), power contactors, magnetic solenoid valves, and electromagnets. Assume a peak inrush current of approx. 10-times rated current, and keep this within the specified “Maximum peak current” for the relay.
 
DC1 DC Resistive loads or slightly inductive DC loads. (The switching voltage at the same current can be doubled by wiring 2 contacts in series). Work within relay data (see the diagram “Maximum DC1 breaking capacity”).
DC13 DC Control of electromagnetic loads, power contactors, magnetic solenoid valves, and electromagnets. This assumes no inrush current, although the switch off over-voltage can be up to 15 times the rated voltage. An approximation of the relay rating on a DC inductive load with 40 ms L/R can be made using 50 % of the DC1 rating. If a freewheeling diode is wired in parallel to the load, it can be considered the same value as DC1. See the diagram “Maximum DC1 breaking capacity”


Resources:
General technical information about FINDER relays - PDF
IEC Utilization Categories - PDF
Utilization categories [wikipedia]
Meaning of AC15, DC1, AC1, and DC13 in relay durability curves




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