Save wiring time, complexity, space and material costs.
by Dana Leland

Modern motor protection solutions provide added value compared to traditional overload relays. Today’s motor management relays offer not only the most advanced protection and monitoring options, but also customized starter control. Read on to learn more about how motor management relays save wiring time, complexity, space and material costs.

What Is a Motor Management Relay?

A motor management relay can both control and protect the motor. This eliminates the need to wire complex circuits to achieve desired control functionality. These relays can be configured for multiple control sources and starter profiles. All control signals are sent directly to the relay, with the contactor output changing state based on both control and protection (See Figure 1).

 Basics of a motor management relayFigure 1. Basics of a motor management relay (Graphics courtesy of Eaton)

A traditional overload relay has a fault contact that opens only in the case of a fault. Many overload relays still offer comprehensive protection features that trigger the fault contact due to a thermal overload as well as other current-, voltage- and power-based protections. However, no matter the level of protection offered, the wiring method relies on all control functionality taking place outside the relay. The overload relay is simply a normally closed fault contact wired correctly in series with the control circuit so that a protection event will stop the motor.

For example, let’s explore a traditional circuit for a very simple application—a conventional direct starter with push buttons for local start and local stop and an auto circuit for remote control from a network. There are also two status pilot lights to indicate running and stopped status (See Figure 2).

Start/stop control wiringFigure 2. Conventional starter control wiring: direct starter with local start/stop, auto circuit and status LEDs

Even in this simple application, the user must provide a holding circuit for the start signal (likely through using an auxiliary contact on the contactor) and wire in an auto circuit with a network-controlled output for remote control. Additional wiring and devices may be used for local status pilot lights.

A motor management relay removes the need for this extra wiring but achieves the same control requirements (See Figure 3).

Motor relay wiringFigure 3. Motor management relay wiring: direct starter with local start/stop, auto circuit and status LEDs

A simple user interface provides control and status indication. Control signals can also be sent directly to the device over the network. This is all achieved with a single cable connection to the user interface and the network. The network is already directly connected to the device as it would be in the traditional setup above for device monitoring.

Motor management relays continue to save on wiring time, cost and complexity even when traditional pilot devices are preferred for control. Inputs on the device pre-configure based on the starter profile and control options selected.

Control signals such as start, stop, auto and device reset may be wired directly to on-board I/O (See Figure 4). This removes the need for holding circuits, separate auto circuits, etc.

Motor management relay wiringFigure 4. Motor management relay wiring: direct starter with local start/stop via fieldwire, auto circuit and status LEDs


The simple examples above help demonstrate how motor management relays differ from traditional overload relays. Even in basic starter applications, this simple technology can save time, money and space.

The benefits only increase as starter logic becomes more complex, such as two speed or reverser applications with multiple contactors or applications involving other devices such as mechanical timers used in Wye and Delta applications.