3 Pole 2-Element Thermal Overload Relay

In the field of three-phase motor protection, how to achieve the best balance between core functions and costs is an eternal engineering topic. The China SPX 3 Pole 2-Element Thermal Overload Relay is a typical product under this concept. It is not a compromise in functionality, but a sophisticated "design optimization" aimed at a wide range of application scenarios where three-phase loads are relatively balanced and the sensitivity requirements for phase failure protection are at the standard level. By cleverly utilizing the thermal coupling effect of two components to detect anomalies in three-phase current, it simplifies the structure while maintaining reliable overload protection, providing a cost-effective protection option for a large number of standard equipment such as fans and pumps.

Features:

Two heating elements are connected in series to two phases (such as L1 and L3) in the three-phase circuit of the motor. When the motor is overloaded, the current flowing through these components increases, and the heat generated causes the corresponding bimetallic plates to bend.
The deformation of two bimetallic plates is synthesized through a common differential lever mechanism. The thermal effect generated by the overload of any one or two phases will accumulate and ultimately drive the action of the trip mechanism. For three-phase balanced overload, the protection response is basically the same as the 3 Pole 2-Element Thermal Overload Relay.
This is the most fundamental difference. In the event of a phase failure (such as L2 phase disconnection), the dual element relay can still detect the fault by raising the current of the two phases (L1 and L3), but its response speed may be slightly slower than the three element relay optimized for phase failure protection. However, for most standard applications, their protection is still timely and effective.
Reducing one heating element and related structure directly lowers material and manufacturing costs, while potentially making the high quality 3 Pole 2-Element Thermal Overload Relay more compact in size.

Advantage

For the majority of three-phase balanced loads in the power system, such as standard pumps, fans, and compressors, their overload protection performance is no different from that of three element relays.

A streamlined structure means fewer potential points of failure. The core bimetallic anti time limit protection mechanism is still strong, maintaining the classic advantages of thermal relays such as strong environmental adaptability, no need for auxiliary power supply, and anti-interference.

The STH-N50 Thermal Relay Is Suitable For S-C50/95 AC Contactor

Frame(A)	STH-N60
Suitabie AC contactor	S-C50/95
Aux contact structure	Manual or Auto retum
Adjust range selcet(A)	Select(A)		Adjust range(A)
	15A		12~18
	19A		16~22
	22A		18~26
	29A		24~34
	35A		30~40
	42A		34~50
	54A		43~65
	67A		54~80
	82A		65~93
	95A		85~105
Aux contact structure	1a1b(1NO+1NC)
Outline and installation dimension
	Type	L	W	H	ΦD
	TH-N60	89	57	83.5	4.5