3-phase Solid State Relays and Contactors

A three phase Solid State Relays (SSR) is 3 individual single phase SSRs packaged in a single housing with a common input so that each SSR is energized simultaneously. In fact, it is not unusual to use 3 individual SSRs to switch a three-phase load but this is of course usually done when a three phase SSR is not suitable for one reason or another. However, the more common and simplistic approach is to use a three phase SSR as it simplifies wiring and usually reduces overall space requirements within the panel.

The main advantages of SSRs, whether single or three phase, are known : high speed switching, long service life, very low energy consumption, shocks and vibration resistance, specific choice of switching time, …

Let us introduce you the main features of celduc®’s range of 3-phase Solid State Relays.

Features of celduc®’s range of 3-phase Solid State Relays

celduc’s three-phase Solid State Relays are available in panel mount and DIN rail mount, with a wide range that can handle up to 125 amps/690 VAC.

Sightpac (45mm installation width) and cel3pac (100mm installation width) Series are designed to switch various loads such as heating elements, motors and transformers.

Various models are capable of handling resistive loads up to 64A and motor loads up to 32A when used with a suitable heatsink. These relays have a built-in VDR or TVS, depending on models, which secures transient protection for heavy industrial applications. Our 3-phase SSRs are available in both AC and DC control versions with a built-in LED status indication.

Here are the main products features

  • Up to 125A / 690Vac
  • AC or DC input voltage
  • Zero voltage control (zero cross relay) or instantaneous control (random relay)
  • 3-phase control with 2 or 3 phases switched
  • Versions with internal protection by RC snubber are available
  • Overvoltage protection is available as either a VDR (MOV) connected across the output terminals of the SSR or a TVS in series with the gates of the thyristor
  • Green LED used to indicate input status
  • Compliance with cURus, CE, UKCA, S-Mark and EAC Standards

Sightpac® Serie : Space-saving design

Sightpac® is a compact version with 45mm installation width and is a market favorite since it has been launched in 2017.

Celduc® offers different connections :

  • Configuration 1 : On the power side we offer standard connection with screws and on the control side we offer pluggable connector for easy and fast connections.
  • Configuration 2 : Connection on the power side is with spring connectors (“push-in” spring type double connectors) which is a simple connection without physical constraint and  without tools. And connection on the control side is with a pluggable connector.

Cel3pac® Series : improved connections to increase switching current limits

Cel3pac® Series has a 100mm installation width and is available with ratings up to 125A per phase, with either AC or DC input and with instant (asynchronous) or zero cross (synchronous) switching.

celduc® offers different connections :

  • Configuration 1 : Connection on the power side and control side with screws. The size of terminals on the power side is up to 50mm² (AWG0 / AWG1), which increases the switching current limits to higher levels than  other SSRs on the market.
  • Configuration 2 : Connection on the power side with M5 screws and connection on the control side with 4-pole pluggable connector
  • Configuration 3 : Connection on the power side with spring connectors for Fast wiring, even in tight spaces (Wiring 100% secure, 70% faster). And connection on the control side with 4-pole pluggable connector

Version with a temperature alarm

celduc® relais offers SGT8650810 equipped with a temperature alarm. In this model, a built-in temperature sensor informs the operator when the maximum recommended temperature is exceeded, which could destroy the product or lower its lifespan. When the temperature is over 70°C, the alarm output is activated.  When it occurs, we recommend that the user takes action based on this alarm output.

Advantages of selecting three phase SSRs with Integrated Heatsinks

celduc® relais supplies “Ready to use” versions with integrated heatsinks which are available in either DIN rail mount or panel mount. SSRs with integrated heatsinks are the easiest to select because most of the thermal calculations have already been considered in its ratings.

In case you want to select three phase SSRs with separate external Heatsinks, please refer to our white paper for a proper heatsink selection.

SMT Series – sightpac® – “ready to use” with integrated heatsink

SGT Series – cel3pac® – “ready to use” with integrated heatsink

Three-phase applications

Three-phase resistive heating applications

For three phase resistive heating applications, zero-crossing three phase SSRs are commonly used. These versions will switch power to the load at the zero-voltage crossing point of each phase in order to minimize inrush currents.

SMT9 Series  – SGT9 Series

Three-phase motor loads applications

To control three-phase motors, we recommend the use of zero-crossing three phase SSRs designed for heavy duty load.

SMT8 SeriesSGT8 Series

Three-phase inductive loads applications

Random turn-on SSRs are recommended for switching inductive loads, such as compressors or transformers where it is desirable to switch on 3 phases on at exactly the same moment.

SGT7 Series

Motor Reversing Applications

Some loads require a motor control that not only energizes the motor, but also reverses its direction of rotation when needed. Celduc® is offering motor-reversing solid state relays as well.

Important remark : SGR and SMR motor reversers have a built-in interlock circuit that prevents the “forward” and “reverse” relays from turning on simultaneously!

So a motor-reversing SSR offers two significant advantages :

  1. all four SSRs are contained in one industry-standard three phase SSR package thus minimizing wiring connections;
  2. the interlock circuit is already built into the SSR.

SMR Series : up to 2.2kW AC-53 (3HP)

SGR Series : up to 7.5kW AC-53 (10HP)


Solid State Relays, whether single or three phase, are ideal for the control of three phase motors and heaters. Proper selection of the SSR for every application requires knowledge of the power rating, operation voltage, ambient temperature and wiring configuration. A variety of SSRs are available for a wide range of operating conditions, in either Panel or DIN rail mount configurations. If you require any additional information, please don’t hesitate to contact our sales and technical teams.