What is a thermal Overload Relay?
Thermal Overload Relays (TOR) use the bimetallic strip principle, in which overload current heats the strip, forcing it to bend & trip the circuit.
They have a slower response since tripping is dependent on heat buildup and can be altered by ambient temperature, resulting in earlier (or) delayed tripping.
TORs provide modest accuracy (±10-20% inaccuracy) and are usually employed for basic overload prevention without advanced functions.
They are inexpensive, simple to maintain, and ideal for basic motor protection applications.
How to Reset a Thermal Overload Relay?
When set to H or HAND, the RESET button must be manually pressed to reset the overload relay following a tripping occurrence.
When set to A or AUTO, the overload relay will automatically reset following a tripping event.
What is an Electronic Overload Relay?
Electronic Overload Relays (EOR), on the other end utilize current sensors & electronic circuits to detect overloads with pinpoint accuracy.
Their tripping action is quicker, unaffected by the ambient temperature & frequently programmed for appropriate current/time characteristics.
EORs give highly accurate performance (±1-5% inaccuracy) and additional protections, including phase loss, imbalance & stall detection.
Many types feature LCD screens, diagnostics, and communication features.
Despite their higher starting cost, they are appropriate for essential and accurate protection needs in current motor control systems.
What is the Principle of Overload Relay?
Overload relay works on the thermal sensing principle, which involves monitoring the heat created by the motor throughout operation.
When the motor draws an excessive amount of current for a lengthy period of time, signaling a potential overload, the thermal overload relay trips and disconnects the motor’s power supply.
Difference between Thermal Overload Relay (TOR) and Electronic Overload Relay (EOR)
Thermal Overload Relay (TOR) vs Electronic Overload Relay (EOR)
Comparison Table
| Thermal Overload Relay (TOR) | Electronic Overload Relay (EOR) |
|---|---|
| TOR operates on the bimetallic strip principle, in which heat bends the strip and trips the circuit. | EOR detects overloads with current sensors and electrical circuitry. |
| TOR responds slowly because it relies on heat buildup. | EOR responds faster thanks to its configurable trip parameters. |
| TOR accuracy is moderate, ranging from ±10-20%. | EOR is highly accurate, often within ±1-5%. |
| Ambient temperature has an effect on TOR performance. | EOR effectiveness is unaffected by ambient temperature. |
| TOR provides just modest overload protection. | EOR provides overload, phase loss, imbalance & stall protection. |
| Tor has a simple manual (or) automatic reset. | EOR supports manual, automated, and remote resets. |
| TOR is inexpensive and suitable for simple applications. | EOR is more expensive yet ideal for important accuracy applications. |
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