Abnormal heat from electrical products can quickly become a serious fire hazard. As such, Calco Electric provides high-quality thermostats, including organic and pellet-type cutoffs. Let us take a closer look at how they work, how to choose the right model, and how to install and use them safely.

Pellet-Type Cutoffs and How They Work

Pellet-type cutoffs are non-resettable thermal fuses. They interrupt the electrical current once a predetermined temperature threshold has been reached. The core of the device is a heat-sensitive, electrically insulated organic pellet. Under normal conditions, this pellet holds a spring-loaded contact firmly against a fixed contact, allowing current to flow through. When the preset temperature is exceeded, the pellet melts, releasing the spring and breaking the circuit. Pellet-type cutoffs are ideal for the following:

• Household appliances
• Electronics
• Office equipment
• Audiovisual systems
• Communication devices
• Measurement tools
• Select transportation components

For applications requiring an inexpensive limit protector with lSA capability, you can count on Calco Electric’s DF Series. We offer standard, long, and custom pellet-type cutoffs.

Determining the Proper Series

Our DF Series includes multiple components. To protect your system, identify the correct operating temperature parameters using the following values:

• Tp: The maximum temperature your product will reach during normal use.
• Th: The safe operating temperature range for the pellet-type cutoff.
• Ts: 24ºC (Tp−Th). If Tp exceeds 170ºC, use 35ºC instead of 24ºC.
• To: The temperature increase caused by the product’s electrical load.
• Heat from the lead wire
• Ventilation or enclosure airtightness
• Location of terminal connections
• Insulation thickness of the surrounding material
• Voltage fluctuation tolerance in your device

Determining the Safe Temperature Range

When selecting pellet type cutoffs, it is vital to ensure they operate safely under all conditions. Even after the pellet melts, residual heat within the cutoff body can continue to rise. This temperature increase must stay below a certain threshold. Also, the general area where you place the cutoff should never exceed its safe temperature range during normal operation. Here are key temperature specifications to understand:

• Functioning Temperature (TF): The temperature at which the cutoff opens the circuit with only 10mA or less current. Tolerances are +0°C / -10°C per UL and CSA standards.
• Holding Temperature (TH): The maximum temperature at which a thermal cutoff can operate while continuously conducting its rated current for 168 hours without activating.
• Maximum Temperature (TM): The maximum temperature at which the thermal cutoff can maintain its mechanical and electrical properties for 10 minutes without resuming conductivity after activation.

Installing Pellet-Type Cutoffs

Safe and effective function is impossible without proper installation. When mounting pellet-type cutoffs, always follow these best practices:

• Mount the device where heat is distributed evenly across the body.
• Use longer lead wires to increase the surface area exposed to heat.
• Secure the cutoff to prevent mechanical stress on the leads or the body.
• Allow enough space for safe and secure mounting.

If you need to bend the lead wire, do so at least 3 mm away from the body of the cutoff. The body should remain stable and free from mechanical force at all times. During soldering, the sealant that joins the lead wires to the case can soften; do not move the leads or body while the solder is cooling. The sealant will regain strength after cooling, which should be at least 30 seconds for manual soldering and at least five minutes for automatic wave soldering.

Safe and Proper Performance

Pellet-type cutoffs are highly effective when used correctly. Remember that these devices respond to excessive ambient temperature, not current overloads. They cannot limit current. Do not install pellet-type cutoffs in liquids, corrosive atmospheres like sulfur gases, or high humidity environments. They are also unsuitable for aerospace, aviation, nuclear power, or life support systems. Always select models based on the listed specifications and test them under conditions that closely mimic real-world use. Secure installation should reflect your final production setup.

Find the Right Pellet-Type Cutoffs

When safety is on the line, quality matters. Because every industry has specific demands, professional guidance is valuable. At Calco Electric, our experts are ready to help you choose pellet-type cutoffs for your application. Trust us to deliver excellent pricing, product quality, and customer service. Learn more about pellet-type cutoffs or request a quote. Contact Calco Electric today.