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3 2 1 Guide to Industrial AC motor starters


Starting an electric motor has come a long way since Schneider’s Telemecanique invented the first contactor in 1924.


This safety innovation – designed to avoid operators electrocuting themselves by changing the manual connection of electrical power to a motor into a remote function – has over the decades been followed by several other key technologies.

Today a motor starter has four basic functions – switch disconnection, protecting against short-circuits, protecting against overload, and control (start-stop) through the contactor. These four functions are typically delivered by one, two or three devices.

Typical multi-device solutions are as follows:

  • “3-device” solution – comprising magnetic circuit breaker, a contactor and an overload relay.
  • “2-device” solution – comprising a thermal magnetic circuit breaker and a contactor.

Both combinations call for work to be done to ensure the devices are compatible and can be coordinated correctly to start and control the motor.

Added to these basic functions is a plethora of optional add-ons, including phase reversal and communication modules, enabling the motor starter to “speak” to PLCs and control rooms.


A single device, known as a starter-controller or Control and Protective Switching device (CPS), includes all starter motor functions in one product.

There is no problem of coordinating devices, and it is easy to install, requiring far less wiring than traditional multi-device solutions. They also take up less space on a control panel.

For example, Schneider Electric’s TeSys U motor starter guarantees total coordination between protection and contactor functions according to IEC 60947-6-2. It only requires three wires, compared to up to 12 for multi-device installations and it is just 45mm wide.

This really is the simplest way of controlling a motor.

TeSys U 

 The TeSys U motor starter combines all motor starter functions into a single product. And its modular design also means a wide variety of more advanced functions can be added.












If you only need basic functionality, then the Tesys U comprises the following:

  • Power Base - For assembling components, ON/OFF operation and resetting. Two power bases available: 12 A and 32 A. Direct starter and reversing starter models available.  Power pole status indication with inbuilt auxiliaries.
  • Standard Control Unit - Performs all the electrical protection functions, including overload, phase imbalance and short circuit protection.
  • Optional additional auxiliary contacts - for additional power pole status and starter status (ready/tripped/off)

For those looking for more from their motor starters, the following additional modules can be assembled on the power base:

  • Advanced Control Unit – facilitates the simple function modules below or additional functions/diagnostics when using the communications modules.
  • A choice of 4 simple function modules - Thermal overload alarm; Indication of motor load; Thermal overload signalling and manual reset; Thermal overloaded signalling and automatic or remote reset.
  • A choice of 6 communication modules - AS-Interface; Profibus DP; CANopen; DeviceNet; Advantys STB; Modbus.
  • Multifunction Control Unit – for full diagnostics (fault history, local display…) and additional control functionality (ground fault protection, jam protection…)

Talking motor starters

The Industrial Internet of Things (IIOT) is touching all areas of industry, and motor starters are no exception.

Communication from devices is now an almost mandatory function, and Tesys U’s ability to accommodate six different types of communication protocols is a reflection of this.

With communication modules such as Modbus, and Profibus, the running of the motor can be monitored and controlled from a distance. 

Ethernet connectivity can be achieved using a gateway, however, the simplest solution is to use the Advantys STB communication module with an Ethernet NIM (Network Interface Module).

Apart from being useful for integrating protection into the industrial automation process, communication can also contribute to the following:

  • early warnings to anticipate the appearance of a defect
  • create log files to record and identify a recurrent event
  • help with implementation
  • help with maintenance by identifying a loss of accuracy in the operating conditions.

Tesys U turns a motor starter into a vital asset in plant operators’ mission to reduce downtime, and improve efficiency and safety.

Compact. Flexible. Smart. Easy to maintain. Why wouldn’t you go all-in-one with Tesys U?

I'm the TeSys product marketing manager at Schneider, based in Coventry, UK. Responsible for Motor Control and Protection which includes contactors, circuit breakers and overload relays.

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