E300 overload relay

It’s no secret that motors are the backbone of manufacturing. Therefore, maintaining optimal health of a motor is a critical and endless focus of plant operators.

At the heart of any motor is the overload relay, which – historically – protects the motor by detecting and reacting to temperature changes in the current.

Thermal overload relays, specifically the bimetallic overload relay, are the most common type of relay used industry-wide. Why? Because they are fairly inexpensive and they work.

However, motors fail for a number of reasons, including uneven power load, wiring or insulation issues, and more. Conventional relays are ineffective when it comes to diagnosing the reason for failure and serve only to shut down the motor in critical situations.

In its simplest form, if the motor is in danger of overheating, the overload relay will flip and cut power to the motor. Pretty straightforward stuff. The problem with this, however, is that the action is reactive not proactive. The time lost while the motor recovers is critical to the bottom line.

Traditionally, once the motor is shut down, time-consuming troubleshooting begins in an effort to get the motor operational again. There is no real predictive or diagnostic data to pull from conventional relays; therefore, it’s impossible to know when an event is about to occur or even why an event occurred in the first place.

Protective relaying has evolved in utility power and industrial systems since protection was introduced more than 100 years ago.

Enter the “smart” electronic overload relays.

Motor protection at the push of a button

The surge in Ethernet adoption is changing automation as we know it. And, at the device level.

Newer, smart overload relays offer advanced motor protection and the ability to see and use real-time data — independent of a central processor. Now instead of reacting to a disrupted motor, modern electronic overload relays — like Rockwell’s E300 — make it possible to predict problems before they happen. What’s actually happening inside the motor can be monitored in real time. The insight this provides is priceless.

e300 overload relay

According to Electrical Research Associates (ERA), nearly half of all motor failures are caused by electrical problems, such as overload, jam, phase imbalance and ground fault, just to name a few.

There are multiple level alarm settings and thresholds that can be programmed depending on specific needs, thus providing much better motor protection than standard electronic overloads. This eliminates the need to watch or check the motor constantly, recording data after the fact using clipboards and grease pens.

For instance, smarter electronic overloads can sense when the load current drops below acceptable levels. This type of sensing is particularly helpful in pump applications, where fluid loss can result in motor damage. Advanced overload relays will alert maintenance personnel before a pump runs dry, which can lead to overheating.

Easy configuration of the overload relay allows for process data to be continuously monitored (even remotely), assuring instant detection of any potential motor failure.

Maybe one of your plant KPIs is to reduce energy costs. In this case, it’s imperative to track every motor to see how much current each is pulling. The E300 will monitor – in real time – the performance of each motor. Depending on the parameters you set, you will receive an alert (email, text message or an audible alarm) telling you when a motor is running higher than normal. This real-time knowledge allows for scheduled downtime to make adjustments or repairs as needed.

That’s just one example of how incorporating a smart overload relay can push the needle on plant metrics. Ultimately, the E300 can detect and protect against a wide range of damaging conditions.


The E300 also samples voltage, temperature and vibration data. This data can be correlated with other system variables such as process speed and used for optimization. The implications to OEE are real.

The diagnostic information available from an electronic overload relay is empowering when it comes to real-time decision making and predictive maintenance. Data available includes:

  • Device status
  • History of past five trips
  • Trip status
  • History of positive warnings
  • Warning status
  • Hours of operation
  • Time to an overload trip
  • Number of starts
  • Time to reset after an overload trip
  • Trip snapshot

In a plant where response time is critical, having status access within the device itself versus a central controller is paramount to uptime. The communication options of the E300 overload relay allow users to view this diagnostic information using the following methods:

  • Logix add-on profile
  • Web browser
  • FactoryTalk® View
  • Faceplates

Another smart benefit to end users – and this is true of most new add-on devices – is the elimination of relying on outside software or IT experts to integrate and/or fix issues. Now maintenance personnel can use a simple web browser to easily integrate and monitor the overload relay from within the PLC or Logix platform. If a motor does trip, the E300 will capture all the data about why the event occurred and maintenance personnel can use this information to prevent future breakdowns.

Intelligent motor protection is a necessity for any plant on the path to modernization. Having the foresight to take action before a failure occurs will save you thousands of dollars resulting from unwanted downtime.

E300 Application Example

Here’s an example of how the E300 saved one plant roughly $50,000.

A manufacturer of railroad ties was relying on a eutectic alloy overload relay to protect the motor on its grinder. The motor, rated at 500-525 amps, was experiencing intermittent trip incidents. Resetting the motor was the first line of defense in order to avoid costly downtime, and troubleshooting was cumbersome given the limited diagnostic ability of the overload relay. After some consultation, it was determined that a new electronic overload relay – in this case the E300 – would help uncover the root cause of the “nuisance trips.” In addition, a meter was placed on the motor to discover any load issues.

Data abstracted from the E300 — which tracked the last five faults — and the meter determined that the motor was being overworked. The 500-525 amp-rated SMC was sometimes running at 950 amps, which was tripping the overload relay. It turns out there were operators who were simply overfeeding the grinder, motivated to exceed productivity goals. Instead of loading 6x6x6-foot trusses, they were loading 12x12x20-foot trusses into the grinder. This activity would have eventually burned up the motor as well as the SMC, potentially costing the manufacturer upward of $75,000 to replace. The smart diagnostic data from the E300 gave insight into the problem and the motor is still functional today.

Learn more:

How to Configure the E300 using Diagnostic Station

Motor Protection Solutions (specifically pages 6-7)

How to Configure the E300 using Web Server

Configure Communications between E300 and PanelView Plus

E300 Multimedia brochure




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