Motor Auto-Restart Relay for Controlled Restart After Momentary Power Loss

The ATC Diversified Electronics MAR Series Motor Auto-Restart Relay provides controlled automatic restart of a motor following a momentary drop or interruption of the 120 VAC control voltage. When the motor was operating before the voltage disturbance and acceptable control voltage returns within the configured undervoltage time, the MAR Series can bypass the START switch and re-energize the motor starter coil after an adjustable restart delay.

The relay is designed for applications where a brief control-power interruption would otherwise require an operator to manually restart equipment. Adjustable undervoltage and restart delays allow the control sequence to be matched to the application and can be used to stagger the restart of multiple motors rather than allowing all equipment to re-energize simultaneously.

The MAR Series also distinguishes between a qualifying control-voltage interruption and an intentional STOP pushbutton operation. If the STOP circuit is operated, the automatic-restart timing sequence is terminated. If the voltage interruption lasts longer than the selected undervoltage delay, or if the motor was not running when the voltage failed, manual restart is required.

Why Use the MAR Series Motor Auto-Restart Relay?

Automatic Restart After Brief Voltage Interruptions: The MAR Series can restore a previously running motor after a qualifying momentary control-voltage disturbance without requiring an operator to press the START button.

Adjustable Undervoltage Timing: Depending on the selected configuration, the undervoltage delay can be adjustable from 0.2 to 6 seconds or 0.2 to 10 seconds, with another configuration providing a fixed 4-second delay.

Adjustable Restart Delay: Available configurations provide restart-delay adjustment from 0.2 to 60 seconds or from 2 to 120 seconds, allowing motor restarts to be delayed after acceptable control voltage returns.

Stagger Multiple Motor Restarts: Different restart-delay settings can be used on multiple motors so their starter coils are not commanded to re-energize at the same instant following restoration of control power.

Distinguishes STOP Commands from Power Loss: Operating the STOP pushbutton de-energizes the MAR output and terminates the timing sequence, preventing an intentional stop from being treated as a momentary power failure.

Plug-In Configurations: The MAR Series is available in 8-pin and 11-pin plug-in models, including versions with an overload-relay L2 disconnect feature.

Industrial Relay Output: The MAR Series provides an SPDT output relay rated Pilot Duty B150, 360 VA, and 10 amps at 120 VAC resistive.

How the MAR Motor Auto-Restart Sequence Works

While the motor is running, the MAR Series monitors the 120 VAC control voltage. If that voltage drops below the undervoltage trip point, the undervoltage timing period begins.

If control voltage rises above the restart-voltage threshold before the undervoltage delay expires, the MAR Series begins its adjustable restart delay. When the restart delay is complete, the internal relay energizes for the specified output interval to provide the motor restart command.

If control voltage remains below the required level longer than the undervoltage delay, the MAR Series does not automatically restart the motor when power returns. Manual restart is required. The same is true if the motor was not operating before the control-voltage interruption.

Undervoltage and Restart Voltage Monitoring

The MAR Series monitors a 120 VAC, 50/60 Hz control circuit. ATC specifies a factory-preset undervoltage trip point of approximately 92 VAC, internally adjustable from 70 to 100 VAC.

The factory-preset restart-voltage point is approximately 102 VAC and is established approximately 10 VAC above the selected undervoltage point. This separation helps define when the control voltage has recovered sufficiently for the restart-delay sequence to begin.

Available MAR Restart Timing Configurations

ATC offers multiple MAR delay configurations to support different restart requirements. Depending on part number, available combinations include adjustable undervoltage delays from 0.2 to 6 seconds or 0.2 to 10 seconds, restart delays from 0.2 to 60 seconds, or a fixed 4-second undervoltage delay with a 2 to 120 second restart delay.

Restart-output intervals are available as continuous, fixed 5-second, or fixed 1-second outputs depending on the selected model configuration.

Motor Restart Control for Industrial Equipment

Motor auto-restart control can be useful on industrial equipment where a short control-power interruption can stop a process even though normal power returns almost immediately. Applications can include pumps, conveyors, processing machinery, material-handling systems, mixers, fans, and other motor-driven equipment where automatic reacceleration is appropriate for the machine and process.

Automatic restart should only be used where restarting without direct operator action is appropriate for the equipment and application. Machine safety requirements, interlocks, overload protection, emergency-stop circuits, process conditions, and applicable electrical requirements must all be considered as part of the overall control-system design.

Find the Right MAR Motor Auto-Restart Relay

Selecting the right motor auto-restart relay configuration depends on the required undervoltage delay, restart delay, restart-output duration, 8-pin or 11-pin termination, overload-relay interface requirements, starter-control circuit, and the operating sequence required by the machine.

Explore the MAR Series above to compare plug-in and delay configurations for controlled motor restart following qualifying momentary control-voltage interruptions.