Utilization categories for Solid State Relays & Contactors ?

It is necessary to select the correct rating of switchgear or controlgear for any application. Therefore, during selection, it is necessary to know the characteristics of the load. The International electrotechnical commission in their standard for low voltage switchgear (IEC 60947) as well as in their standard for safety requirements for Solid State Relays (IEC 62314) has defined utilization categories to simplify the selection of devices.

What are the utilization categories ?

The standard utilization categories define the nominal current values for relays and contactors.

They depend on the following:

  • The type of load to be controlled (squirrel cage motor, resistors etc.)
  • The operating cycle conditions (motor running or starting, reverse operation, etc.)

Utilization categories are used for a simplified device selection

Electrical systems often involve loads being switched on and off for operation of equipment. When designing a system that is switching an electrical load it is important to choose the correct component that will switch the load on.

In order to select the proper component for the application, it is first necessary to determine the operating characteristics of the load to be controlled. As an example, for a normal resistance load, the starting current in cold conditions is x 1,4 the nominal current. On the other hand, some applications, such as motors, can consume many times the rated operating current during the phase when they are switching on and accelerating.

For a simplified device selection, the International Electrotechnical Commission (IEC) defined several utilization categories. Utilization categories are defined in the standards for low-voltage switchgear This makes the selection of appropriate Solid State Relays much simpler, and ensures the maximum safety of electrical equipment so it doesn’t overload.

What are the relevant IEC product standard for celduc Solid State Relays & Contactors ?

The Relevant IEC product standard for Solid State Relays & Contactors are :

IEC 60947-4-2 : Semiconductor motor controllers and starters

IEC 60947-4-3 : AC semiconductor controllers and contactors for non motor loads

IEC 62314 :2022 : Solid-state relays – Safety requirements

Here are the commonly used Utilization Categories

The commonly used utilization categories in our technical documentation are AC-1 and AC-3 but you will find the complete list at the bottom.

AC-1 (previously AC-51)

This category applies to all AC loads where the power factor is more than 0.95. These are primarily non-inductive or slightly inductive loads, such as resistive loads.

AC-3 (previously AC-53)

This category applies to squirrel cage motors with breaking during normal running of the motor.
On closing, the SSR makes the inrush current, which is about 8 times the rated full load current of the motor. On opening, the SSR breaks the rated full load current of the motor.
The rating for this category is usually lower than AC-1 because of high inrush current switching.

Utilization Categories used in the IEC 60947 Series

AC-1 Non-inductive or slightly inductive loads; resistance furnaces

AC-2 Slip-ring motors: starting, switching off

AC-3 Squirrel-cage motors: starting, switching off motors during running

AC-4 Squirrel-cage motors: starting, plugging, inching

AC-5a Switching of electric discharge lamp controls

AC-5b Switching of incandescent lamps

AC-6a Switching of transformers

AC-6b Switching of capacitor banks

AC-8a Hermetic refrigerant compressor motor control with manual resetting of overload releases

AC-8b Hermetic refrigerant compressor motor control with automatic resetting of overload releases

DC-1 Non-inductive or slightly inductive loads

DC-3 Shunt-motors

DC-5 Series-motors

Utilization Categories used in the IEC 62314 :2022 Series

IEC 62314:2022 cancels and replaces the first edition published in 2006. This edition constitutes a technical revision and includes significant technical changes in the load categories with respect to the previous edition.

Alternating current Loads :

LC A Non-inductive or slightly inductive loads

LC B Motors

LC C Electric discharge lamp

LC D Incandescent lamps

LC E Transformers

LC F Capacitives Loads

LC G Self-ballasted lamp load

Direct current Loads :

LC N Control of resistive DC loads and photocoupler isolated static DC loads

LC O Control of direct current electromagnets

LC P Control of direct current electromagnets having saving resistors in the circuit

LC Q DC motor direct start

LC R Direct current incandescent (tungsten) lamps

How to select the appropriate rating for our SSRs ?

All our Solid State Relays & Contactors are characterized by the utilization category together with the rated operational voltage and current indicated.

Therefore, in our data-sheets we specify both AC-1 and AC-3 rated currents for products suitable for all kinds of loads.

For example, if we declare that a Solid State Contactor has an AC-3 rated current of 16A at 400V means that this contactor can control motors with a maximum rated current of 16A at 400V (when mounted on a proper heatsink). The standard requires a long series of tests to confirm the conformity of the product to the control of such motors.

When non-specified, celduc’s SSRs current rating given are based on the AC-1 rating. For maximum nominal current value for other loads, please refer to our technical data-sheet.

To conclude

The two main types of ratings that are used for Solid State Relays & Contactors are AC-1 / LC A and AC-3 / LC B.

AC-3 rating should be used for inductive loads. The AC-3 rating is always lower than the AC-1 rating and if the application is not known this rating should always be used. The second type of rating is AC-1, which is always higher than the AC-3 rating and is used for resistive loads and is most often related to heating applications.

Well knowing which rating you need can simplify our SSR selection and you should check in our data-sheets whether the rating is for AC-1 or AC-3. Furthermore, some of our products are suitable for all kinds of loads, and others are dedicated to AC-1 resistive loads.