Introduction: Choosing the right thermal overload heater ensures reliable motor protection from overheating and phase faults. The table below summarizes selected units that cover common HVAC, compressor, pump, and industrial motor needs. Each option is described with key features to help match capacity and functionality to your application.
This Square D B45 unit is listed as a replacement heater element, identified by SKU B426782 (CTO). It is designed to fit compatible motor starter and overload relay assemblies that accept Square D heater elements. As a heater element replacement, it’s intended for restoring proper overload trip characteristics when matched to the correct relay and motor full-load current.
Key considerations: verify compatibility with the existing Square D relay model and confirm the ampere class required for your motor. Replacement elements are typically specified by catalog numbers and amp ranges—installing the proper element preserves intended trip response and thermal calibration.
The Square D B28 heater element is offered in a used—but described as good—condition. Product dimensions and weight are provided, useful when confirming physical fit inside a starter assembly. Replacement elements like the B28 are typically selected by their ampere rating and mechanical compatibility with the relay base.
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When sourcing a used heater element, check for signs of wear and ensure the element’s resistance and mounting hardware are intact. For installations where precise trip curves and reliable thermal response are required, cross-reference the B28 with the relay’s specified heater table to confirm proper protection for the motor’s full-load current.
The Square D B50 heater element is listed as brand new with an amp rating of 29.1–30.7 amps. This amp range positions the B50 for mid-sized motors where that full-load current (FLC) band applies. Heater elements are a common way to tune thermal overload relays to the motor they protect by selecting the element with the matching ampere band.
Installers should confirm the relay frame and heater mounting compatibility, then select the element whose amp band covers the motor FLC. Proper selection prevents nuisance trips while ensuring overload protection under sustained overcurrent conditions.
The Schneider DPER16 Easy TeSys is a modular thermal overload relay offering manual or automatic reset, screw clamp terminals, and a protection range that includes 9–13 amps for the listed unit. It supports a wide frequency range and rated insulation voltages suitable for industrial applications.
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Notable features include tripping class 10 for motor protection, compact construction for space-constrained panels, and functionality to protect against phase failure and imbalance. The Easy TeSys family typically integrates with contactors for a compact starter solution and includes test/trip indicators for servicing.
The ZGLEDUN thermal overload relay is specified for 37–50A operation and includes phase-break protection, manual and automatic reset options, temperature compensation, trip indication, test and stop buttons. Its compact physical size is useful for retrofits or new installations where space is limited.
This relay is intended for 50–60Hz circuits with a rated insulation voltage of 690V. The built-in features—such as adjustable range and diagnostic indicators—support straightforward integration with three-phase motors in pumps, compressors, and industrial drives requiring higher current protection.
The Walfront NR2-36 is described as a durable thermal overload relay designed for reliable motor protection with temperature compensation and broad compatibility for 50–60Hz circuits up to a rated insulation voltage of 690V. The product is positioned as a motor protector with emphasis on longevity of materials and consistent performance.
Key functionality includes a thermal trip mechanism with temperature compensation to reduce false trips due to ambient changes. Consider this relay when you need a straightforward motor protector with core overload and phase loss detection features in general-purpose applications.
The Awozkcd KSD301 is an auto-reset thermal thermostat switch rather than a full motor overload relay. It features a bimetal disc sensor with a typical action of closing on rise at 60°C (140°F) and opening on fall at 50°C (122°F). Rated for AC and DC applications with several voltage/current ratings.
This component suits localized over-temperature protection for enclosures, transformers, or auxiliary devices rather than three-phase motor overload protection. Use it where a temperature-triggered switch is required rather than a calibrated motor thermal element or relay.
Buying Guide: Choosing The Right Thermal Overload Heater
Selection of a thermal overload heater or relay requires matching electrical, mechanical, and operational requirements to the motor and system environment. Below are the key points to evaluate before buying.
1. Match Ampere Rating To Motor Full-Load Current
Identify the motor’s full-load current (FLC) from the motor nameplate. For heater elements, choose the element with an ampere band that covers the motor FLC. For adjustable relays, set the relay to the motor’s FLC. Correct matching prevents nuisance trips and ensures timely overload protection.
2. Relay Type: Heater Element vs. Electronic/Adjustable Relay
Heater Elements (like Square D B-series): Installed in thermal relays to tune trip characteristics. Require mechanical compatibility with the relay base.
Adjustable Thermal Relays (like Schneider Easy TeSys, ZGLEDUN): Offer built-in range adjustment, phase-loss detection, manual/auto reset, and trip indication.
Thermostat Switches (like KSD301): For temperature-triggered control, not direct motor overload protection.
3. Trip Class And Time-Delay Characteristics
Trip class (for example, Class 10) defines the time-current characteristics. Choose a class that matches motor start-up inrush and application demands. Higher inertia loads may require different trip characteristics to avoid nuisance trips during startup.
4. Reset Mode And Diagnostics
Decide between manual and automatic reset. Manual reset is safer for unattended fault diagnosis; automatic reset can minimize downtime but may mask persistent faults. Look for trip indicators and test buttons for easier troubleshooting.
5. Voltage, Frequency, And Insulation Ratings
Confirm the relay’s rated insulation voltage and frequency (e.g., 50–60Hz, insulation up to 690V). Ensure compatibility with system voltage and any higher frequency or unusual supply conditions.
6. Environmental And Physical Fit
Check ambient temperature compensation, enclosure protection requirements, and physical dimensions. Replacement elements must physically fit the relay, while integrated relays require panel or contactor mounting space.
7. Phase Failure And Imbalance Protection
For three-phase motors, choose relays that include phase-loss and phase-unbalance protection if the process or application is sensitive to single-phasing or uneven loading.
8. Material Quality And Certifications
Look for reputable brands and relevant approvals where necessary (UL, cUL, IEC ratings). Material quality affects long-term reliability and thermal stability in varying environments.
9. Application Use Cases
HVAC and compressors: Compact modular relays with reset options and tripping class matching start-up profiles.
Pumps and fans: Consider adjustable range relays with phase protection to prevent single-phase damage.
Industrial motors: Use certified relays with clear trip indication and available spare heater elements for field serviceability.
10. Installation And Maintenance Considerations
Confirm wiring terminal type, ease of setting the amp range, and availability of replacement elements. Maintain documentation of relay settings and test periodic operation to ensure protection works when needed.
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