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As the pump application scope more and more widely, both industrial, agriculture, household, environmental protection, energy, etc., involves the pump, but the important core component is the pump of the motor, but the motor burning accident also happen, in real life, motor burned mainly by the following plugging turn coil overheating, excessive load motor overload, lack of phase. Adding a thermal protector is one of the effective ways to protect the motor. Thermal protector, also known as the temperature switch, temperature control switch, etc. Is a kind of bimetallic as a temperature element temperature switch, electrical normal work, the bimetallic sheet in a free state, the contact in the open state, when the temperature rises to action temperature value, bimetallic element heating internal stress and rapid action, open the contact, cut off / on circuit, to play a thermal protection role. When the ambient temperature drops to the reset temperature of the protector, the contact will close the circuit again and the motor will work again. 

How to choose the right protector is very important, otherwise not only can not play a protective role, but because of the selection error of the motor can not work, or even burned.

1. Determine the voltage and current

The motor has different voltage range 380V 230V 220V 110V, DC motor will have 36V 24V 12V, etc., according to different working voltage voltage protector, in principle, the actual application voltage is less than or equal to the rated voltage of the protector, for example, the 380V motor cannot choose the rated voltage 220V protector, and the rated voltage 220V protector can be used in the motor of 110V。

The current of the motor is divided into three kinds: starting current, normal working current and blocking current. The rated current of the protector is greater than the maximum of the three currents, and there needs to be left. For example, if the normal operating current of a motor is 1A, the starting current is 1.5A, and the blocking rotating current is 2A, the rated current of the protector is at least 2A, and it is best to choose the rated current of 3A or 5A to keep the margin. Some motor start current is greater than the rated current of the protector, but the start time is short, and the normal working current and blocking current are less than the rated current of the protector. In this case, this protector can also be selected. Although the starting current is greater than the rated current, but due to the short time, the current thermal effect has not had time to make the double sheet heat leading to the protector protection, so as not to cause misoperation.

2. Choose to protect the temperature

  • The choice of protection temperature is related to three factors: insulation level of enameled wire, installation position and protector type.

Temperature grade of the insulation






Max. temperature(℃)






Winding temperature rise limit value (K)






The protection temperature is lower than the maximum allowable temperature, for example, the maximum temperature ofF class is 155℃, and the actual selection can be 145℃ or 150℃.

  • The installation position is divided into built-in inside the coil and bundled outside the coil, because when the motor is blocked and forwarded heat, the overheating phenomenon spreads from inside and outside. If the protector is buried in the interior, the protection temperature is slightly lower than the highest temperature of the enamelled wire; If it is tied outside the coil, consider the temperature difference between the inside and outside, and choose a lower temperature protector. For example, the insulation level is F class enameled wire, coil inside and outside the temperature difference of 20℃, then choose 155-20=135℃ or so of the protector;

3. Type selection of thermal protector

  • Shielding pump: self-priming pump installation position is limited: the coil buried blocking or abnormal, generally heating from the inside of the coil, gradually to the coil surface conduction, if placed on the surface of the coil, there will be delay. Or the same model winding turns more, squeezed the internal space, resulting in the protector can not be installed. (ST01 / ST11, ST01 U10 direct crest is welded to the circuit board with the protector Mimi head close to the coil surface).

    Shielded pump, self-suction pump, submersible pump buried after the integrated pressure. industry in the current solution after plastic dig groove plug or with the false protector built-in integrated and then put in, the true protector damage coil delay production efficiency. (ST01 300N / ST11 500N / ST06 500N).

  • Vacuum into paint: in order to provide insulation performance, the stator is put into the paint tank immersive vacuum, the pressure reaches-0.09 mpa especially water-based paint, fluidity is good, especially easy to enter the protector, the paint into the contacts, resulting in product failure. (ST01 / ST11 unique sealing structure design and process processing, in the case of-0.085 mpa, ST01 paint rate in less than one-thousandth, ST11 to achieve the five elements industry level in about 5%).

  • Using current over double sheet thermal protector, the design needs to consider the current heating lead to the advance jump, and in different environmental temperatures, the advance is different, design more painful ST01 / ST06 / STH 6 / ST11 belongs to the pure temperature protector, working current through the reed, without double sheet, the jump temperature has no big impact, will not lead to early jump, the design is relatively simple.

  • Jet pump, deep well pump, road pump, installation space is limited, but the blocking current is large, the life is long. ST06/STH6/ST12 diameter 9.5mm thickness 6.8mm in the case of AC250V, ST06 current 25A life more than 100 times, STH 6 current in 35A life more than 2000 times, ST12 current 50A life more than 3000 times, the smaller the current life will be higher. The traditional current over the double sheet protector, due to the jump temperature close to the double sheet, a very slow peristalsis process, resulting in too small contact pressure, contact resistance becomes large, at the jump temperature slightly cut off, due to the small opening distance, the arc pulling phenomenon when the jump is serious, resulting in limited life. SAFTTY Protector, the contact is welded or placed on the reed, the double sheet and the reed are independent. However, the temperature is close to the jump-off temperature. When the double chip peristalsis occurs, the contact pressure will not change, and the contact resistance does not change, so it will not lead to the arc pulling phenomenon of micro-cut-off. When the double sheet reaches the jump break temperature, it will quickly reverse, driving the separation of the moving contact on the reed and the static contact on the cover plate. Due to the large opening distance, the arc ablation phenomenon is not obvious.

  • The three-phase pump three-phase motor cannot cut off the three-phase at the same time. Traditionally, one of each phase is installed, or one of any two phases, can not be protected at the same time, easy to cause phase deficiency STY6 STYH at the voltage 400V, STY 6 current 6.3A / STYH current 12A life over 3000 times while cutting the three phase.

  • High power motor uses external overload protector, no blocking, the current is too large, the coil will heat, the traditional high current protector 18AM 2AM 3AM rectangular, large volume, can not be installed on the surface of the coil, feel the temperature of the coil is slow (ST12 250V30A blocking 50A high current protector diameter 12mm thickness 6mm).

  • The insulation layer of the protector is sharp after heat shrinkage, easy to cut the enameled wire, causing short circuit or insufficient insulation voltage resistance. (ST01 U4, BW-B, BW-E shell epoxy sealing, round and smooth, will not cause harm to the enameled wire).

  • Explosion-proof motor protector, due to the poor sealing performance, the protector action arc pulling problem. (ST01 U4 Epoxy envelope sealing).


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Sales:Don Qu

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