Overload Heaters

If you work in an industrial field that uses electric motors, you know the importance of preventing their circuits from overloading. With overload heaters, you can protect your motors from damage, cutting them off at the source to eliminate the harmful effects of overcurrent. Investing in overload heaters for your facility means safeguarding your industrial electronic devices from harm and saving your company time and money.

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What Is an Overload Heater?

Overload heaters are elements of overload relays that protect motors against overcurrent. They are low-resistance metal strips that generate heat as the electric motor pulls power from the current, imitating the thermal qualities of the motor. They do not burn open and break the current directly like a fuse.

While components like fuses and circuit breakers are designed to deliver overcurrent protection to power conductors, overload heaters prevent overcurrent for large electric motors.

How Does an Overload Heater Work?

Heaters are bimetallic, meaning they contain two different metals. One of these metals has a high expansion coefficient, while the other has a low one.

The metallic strips the higher expansion coefficient wind around the opposing metals, which carry the current. Both metals then begin to expand as a result of the heat. However, if the heating components achieve a critical temperature, the higher-expansion metal will enlarge to a greater size than the low-expansion metal.

This uneven expansion causes the metal with the higher expansion coefficient to bend toward the other, triggering a normally closed switch contact and causing it to spring open. The relay coil automatically disconnects from the power supply when the contact opens, cutting off power to the motor.

Advantages of Using Overload Heaters

As the name suggests, overload heaters are essential in the overload protection process for large electric motors. As vital elements of overload relays, these components make it possible to minimize the harmful effects of overloading. Some of the many benefits of overload protection include:

• – Preventing motor damage: Because overload heaters cause switch contacts to de-energize and cut off power to the motor when excess currents pass through the wires, they protect the motor from sustaining damages caused by melting or burning.
• – Minimizing downtime: Circuit overloads can cause complete equipment breakdowns, forcing companies to endure significant downtime while repairing or replacing the motor and other damaged components. Because overload heaters prevent motor damage from occurring, they minimize downtime and losses.
• – Increasing service life: When your motors are safeguarded against the effects of overloading, they can serve their purpose for longer.
• – Saving money: One of the most significant advantages of overload heaters is the cost savings associated with them. Since these components protect electric motors from damages and breakdowns, they can save companies hundreds to thousands of dollars in repair, maintenance and replacement costs.

Overload Heater Applications

Overload relays and heaters are suitable for numerous industrial, residential and commercial devices. Any electrical machine can benefit from overload protection — particularly those that are more vulnerable to overloading conditions, such as:

• – Transformers
• – Motors
• – Generators
• – Home appliances
• – Heaters

How Do You Choose an Overload Heater?

It is smart to select overload heaters of the same size and brand — however, finding these identical components is not always possible. In these cases, there is still a selection plan to which you can adhere to find heaters that best suit your motor.

First, you should consult your motor manufacturer’s selection tables to determine its full load amperage (FLA) and motor starter. These characteristics will impact the type of heater components you should use.

If your motor’s FLA does not match up with the manufacturer’s table, you can choose the closest alternative, assuming your motor and controller function at the same temperatures. If they exhibit a minimal temperature difference, select an overload heater based on the controller’s temperature. You should pick the higher heater number if the controller is warmer than the motor and lower if it is cooler.

If your motor and controller have a more significant temperature difference of 15 degrees or higher, you will have to assume some extra steps to procure a reliable overload heater suited to your motor. To begin the process, be sure to contact the motor supplier or manufacturer to gain additional insights and next steps.

What Are the Different Types of Overload Heaters?

Overload relays and their corresponding heaters all belong to one of four trip classes defined by the National Electrical Manufacturer’s Association (NEMA), indicating the amount of time in seconds it takes for the relays to open due to overload conditions. These four classes and their implications are outlined in NEMA MG-1 and include:

• – Class 5: Heaters and relays of this class are typically used for motors that require exceptionally fast tripping.
• – Class 10: Class 10 components protect artificially cooled motors that function at low thermal capacities, such as submersible pump motors.
• – Class 20: As one of the most common trip class elements, Class 20 overload heaters and relays are suitable for general purpose applications.
• – Class 30: Elements of this trip class are used to prevent nuisance tripping and are usually required for motors with high inertial loads.

What Do You Do if Your Heaters Fail?

Overload heaters can fail for various reasons, meaning you should handle each failure differently.

If your heaters are tripping but your motor is safe and fully functional according to static and dynamic testing, try checking the screws on and around the heaters. Many heater failures can be attributed to loose screws resulting from high temperatures that cause the components to loosen over time, resulting in heater failure. If that is the case for your heaters, you can tighten the screws to resolve the issue.

If the screws holding the heater in place are not loose, your heaters may have simply reached their end. Like any element, overload heaters are subject to wear and tear and can malfunction and fail over time — especially if you have had them for decades. In that situation, the best thing to do is replace them.

When you replace your heaters, be sure to swap out the entire set. Even if only one heater seems to be failing, you should still replace all of them to ensure no damaged heaters remain in the relay and cause continuous failure.

Depend on Global Electronic Services for Your Industrial Workplace Today

If you are looking to purchase overload heaters for your industrial motors, Global Electronic Services has the components you need. We repair and service countless industrial electronics and motors in-house using our factory-trained and -certified technicians. Our team replaces various components with 18-month in-service warranties at 10% less than competitor prices.

Get a quote on one of our many motor repair services today!

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