Thermal Overload Relay Motor Protection

The tragedy of motor burnout often begins with an unnoticed sustained temperature rise. SPX's durable Thermal Overload Relay Motor Protection is the 'terminator' of this covert process. Its role is far from a simple current sensing switch, but rather a sophisticated 'thermoelectric analog system'. Each bimetallic component inside it is a calibrated "thermal model" that reproduces in real time the heating and cooling status of the motor winding under the same current. When the external model determines that the thermal limit has been reached, it means that the interior of the motor is also in danger, and protection is immediately triggered. This is a preventive protection philosophy that originates from physical essence and precedes damage.

Features:

The heating element connected in series to the main circuit directly converts the current into thermal energy in a square relationship (P=I ² R) without the need for intermediate conversion or external power supply, which is the most direct simulation of motor losses.
Thermal energy causes controllable and cumulative bending deformation of bimetallic sheets with specific formulations. This variable is the thermal integral of the time and current functions. When the accumulated deformation reaches the mechanically set threshold, the release mechanism immediately operates, completing a reliable conversion from thermal energy to mechanical energy and then to control signals.
The lifespan of motor insulation materials decreases exponentially with temperature (such as the "10 degree rule"). The inverse time characteristic of Thermal Overload Relay Motor Protection (the greater the overload, the faster the action) perfectly matches it, intervening before the critical point of sharp reduction in insulation life.
Wholesale customized Thermal Overload Relay Motor Protection understands and allows for reasonable overload of the motor during start-up or short-term process requirements, and only takes action when the product of overload degree and time (i.e. "thermal accumulation") exceeds the safety threshold, avoiding unnecessary shutdowns.

Accurate positioning

In modern electronic control systems, various protective devices work together to form a defense in depth system:
Circuit breakers (CB/MCCB) are the guardians of the power grid, responsible for clearing catastrophic faults such as short circuits, protecting cables and system architecture.
Motor protection type thermal overload relay is a close fitting guard of the motor body, dedicated to combating the chronic threat of thermal damage caused by overload and phase interruption.
The internal protection of the frequency converter/soft starter provides process and algorithm level protection, such as overcurrent, overvoltage, etc., but its effectiveness depends on its own health and parameter settings.
Choosing high quality Thermal Overload Relay Motor Protection means adding an independent, pure, and redundant thermal protection layer based on different principles to the motor, which is the highest level of security thinking.

Application

Mining crushers and ball mills; Cement plant roller presses and large fans are designed to cope with high impact and dust environments.
Thermal Overload Relay Motor Protection can be used for fire pumps and domestic water pumps in buildings; Water lifting pumps and sewage treatment blowers are used to protect public safety and people's livelihoods.
The spindle and feed motor protection of plastic injection molding machines and metal processing centers, as well as the thermal overload relay motor protection, maintain the core value and reputation of the equipment.

The STH-T25 thermal relay is suitable for S-M20/25 AC Contactor.

Frame(A)	STH-T18(TH-T18)		STH-T25(TH-T25)				STH-T50(TH-T50)
Suitabie AC contactor	S-M10/12		S-M20/25				S-M35/50
Aux contact structure	Manual or Auto retum
Adjust range selcet(A)	Select(A)	Adjust range(A)	Select(A)		Adjust range(A)		Select(A)	Adjust range(A)
	0.24A	0.2~0.32	1.3A		1~1.6		29	24~34
	0.35A	0.28~0.42	1.7A		1.4~2.0		35	30~40
	0.5A	0.4~0.6	2.1A		1.7~2.5		42	34~50
	0.7A	0.55~0.85	2.5A		2~3
	0.9A	0.7~1.1	3.6A		2.8~4.4
	1.3A	1~1.6	5A		4~6
	1.7A	1.4~2.0	6.6A		5.2~8
	2.1A	1.7~2.5	9A		7~11
	2.5A	2~3	11A		9~13
	3.6A	2.8~4.4	15A		12~18
	5A	4~6	19A		16~22
	6.6A	5.2~8	22A		18~26
	9A	7~11	29A		24~34
	11A	9~13	35A		30~40
Aux contact structure	1a1b(1NO+1NC)
Outline and installation dimension
	Type		L	W	H	φD
	TH-T25		63	51	81	4.5

Production process