CN112863794A

CN112863794A - A temperature sensitive PTC protector

Info

Publication number: CN112863794A
Application number: CN202110314716.9A
Authority: CN
Inventors: 赵鑫建; 曹清华; 王明东; 张伟; 郁益根; 赵电; 石成龙; 邓安甲; 吴国臣; 王军
Original assignee: Shanghai Wei'an Electronic Co ltd
Current assignee: Shanghai Wei'an Electronic Co ltd
Priority date: 2021-03-24
Filing date: 2021-03-24
Publication date: 2021-05-28

Abstract

The invention relates to a temperature-sensitive PTC protection device, which has an overcurrent protection element of PTC conductive composite material and a composite device of bimetallic sheet material, which can be safely and effectively given to low-current motors and vehicle-mounted motors in temperature-sensitive household appliances. Protect. It includes a shell, a pin terminal and a polymer PTC element with upper and lower surfaces, and is characterized in that: the polymer PTC element and the bimetal element in the shell are connected in parallel and supported by an insulating base, and the insulating base fixes the bimetal. The pin terminal of the component and the polymer PTC component, and the bimetal component and the polymer PTC component have a common pin terminal. The invention can effectively prevent the temperature control device from repeatedly appearing in the "open-closed" state during long-term operation, thereby avoiding the occurrence of electric arcing. The invention simultaneously has the dual functions of over-temperature protection and power-off recovery of the existing protector.

Description

Temperature-sensitive PTC protector

Technical Field

The invention relates to a temperature-sensitive PTC (positive temperature coefficient) protection device, in particular to an overcurrent protection element with a PTC conductive composite material and a composite device made of a bimetallic strip material, which can safely and effectively protect a low-current motor and a vehicle-mounted motor in a temperature-sensitive household appliance.

Background

At present, the protectors of the low-current motor and the vehicle-mounted motor in the common household appliance are mostly overcurrent protection or overtemperature protection.

Overcurrent protection devices are roughly divided into two types: one is a fusing protector, which has the defects that the fusing protector can only be used for one-time protection and has the unrecoverable characteristic, and if fusing protection occurs, the fusing protector needs to be replaced again; one is a PTC protector, which has the disadvantage of insufficient sensitivity to temperature, and can not achieve better protection if the inside of the household appliance or the motor contains devices which are easy to damage due to overtemperature.

Overtemperature protection devices are generally thermal protectors based on bimetallic strips, and the operating principle of such bimetallic strip elements is as follows: the thermal protector senses the temperature of the coil, and when the temperature reaches the rated tripping temperature of the bimetallic inner active layer of the over-temperature protector, the bimetallic strip deforms to protect and cut off the circuit; when the temperature of the active layer in the bimetal is reduced to the rated recovery temperature, the bimetal sheet recovers and the circuit is switched on. The over-temperature protection device has the disadvantages that the contact point is easy to generate electric arc sintering contact when working for a long time, so that the protector fails; meanwhile, when the protector recovers is unknown, the state of the motor during recovery is also unknown, and therefore, the safety hidden danger exists.

Therefore, the current motor protectors adopt single protection of overcurrent or overtemperature, and certain potential safety hazards exist in overtemperature protection. If two protection functions need to be considered, a protector with a plurality of functions needs to be connected in series, so that the complexity of the product is increased, and the manufacturing cost of the product is also increased.

Disclosure of Invention

The invention aims to provide a temperature-sensitive PTC protector which has the characteristics of a PTC over-current protector and an over-temperature protection device.

Yet another object of the present invention is to: provides a preparation method of the temperature-sensitive PTC protector.

The purpose of the invention is realized by the following scheme: a temperature sensitive PTC protector comprising a housing, a pin terminal and a polymer PTC element having upper and lower surfaces, wherein: the polymer PTC element and the bimetallic strip element in the shell are connected in parallel through the insulating base, the pin terminal of the bimetallic strip element and the polymer PTC element are fixed by the insulating base, and the bimetallic strip element and the polymer PTC element have a common pin terminal.

The invention not only solves the defect of using a single protector at present, but also has the characteristics of simple structure, quick response to a temperature critical point, long-term working reliability and the like.

On the basis of the scheme, the insulating base is provided with a cutting groove, and the polymer PTC element is arranged in the cutting groove.

Furthermore, the upper surface of the polymer PTC element is connected with the lower surface of one end of the common pin terminal; the upper surface of one end of the common pin terminal is provided with an NO contact which corresponds to the position of a semicircular contact arranged at one end of the bimetallic strip element and enables the two contacts to be in a long-closed state; the other end of the common pin terminal is led out of the shell through a cutting groove of the insulating base; the lower surface of the polymer PTC element is provided with another pin terminal which is connected with the pin terminal of the bimetallic strip element, so that the polymer PTC element and the bimetallic strip element are in a parallel structure.

Specifically, the common pin terminal is a No. 1 pin terminal, the pin terminal of the bimetallic strip element is fixed on the insulating base as a No. 2 pin terminal, the leading-out end of the No. 1 pin terminal extends out of the shell through the cutting groove, one surface of the other end of the No. 1 pin terminal is connected with the upper surface of the polymer PTC element, the other surface of the No. 1 pin terminal is provided with an NO contact, the NO contact corresponds to the position of a semicircular contact arranged at one end of the bimetallic strip element, and the two contacts are in a long closed state; the other end of the bimetallic strip element is connected with a No. 2 pin terminal; meanwhile, the lower surface of the polymer PTC element is provided with a No. 3 pin terminal, and the No. 3 pin terminal is connected with the No. 2 pin terminal, so that the polymer PTC element and the bimetallic strip element are in a parallel structure.

The working principle of the invention is as follows: the bimetallic strip element part of the temperature-sensitive PTC protector is preferentially protected, and when the temperature-sensitive PTC protector is heated, the NO contact is opened to cut off a circuit; meanwhile, the macromolecule PTC element is partially connected into the circuit to start working, and the bimetallic strip element can continuously present an off state by self heat; only when the power supply is turned off, the polymer PTC element does not work partially, and when the temperature is reduced to the rated temperature, the two contacts of the bimetallic strip element can be closed again to recover: initial state of the temperature sensitive PTC protector in the circuit.

Preferably, the No. 2 pin terminal is injected on the insulating base.

Preferably, for convenient connection, No. 2 pin terminals are provided with grooves on the inner side of the insulating base, and No. 3 pin terminals are provided with bending joints, wherein bosses are arranged at the bending joints and are embedded into the grooves.

Preferably, the directions of the output ends of the pin terminal 1 and the pin terminal 2 can be defined as the same side or different sides according to different installation requirements.

On the basis of the scheme, the insulating base is an insulating base with the melting temperature not lower than 145 ℃.

On the basis of the scheme, the bimetallic strip element and the polymer PTC element are positioned in the same space in the shell.

On the basis of the scheme, the conductive polymer base material of the polymer PTC element is formed by mixing a polymer material and conductive powder, wherein the polymer material is one or a mixture of more of polyethylene, polyvinylidene fluoride, polyvinyl chloride, polypropylene, polystyrene, nylon, polycarbonate, polyurethane, polytetrafluoroethylene, polyethylene terephthalate and the like; the conductive powder is selected from: one or more of metal nitride, metal powder, carbon black powder, metal carbide, metal boride and metal silicide.

The invention also provides a preparation method of the temperature-sensitive PTC protector, which comprises the following steps:

step one, preparing an insulating base:

the insulating base is made of a temperature-resistant insulating material, an insulating high polymer material with the melting temperature of more than or equal to 145 ℃ is prepared into the base by a pouring or molding process, an independent cutting groove is processed on the base, and the No. 2 pin terminal is directly fixed on the insulating base by injection molding or fixed on the insulating base by welding, so that the leading-out end of the No. 2 pin terminal extends out of the base;

step two, preparing the bimetallic strip element:

two metal sheets with different thermal expansion coefficients are overlapped and then two ends of the metal sheets are connected and fixed to form a bimetallic strip element, one end of the bimetallic strip element is fixed to the connecting end of the No. 2 pin terminal, and the lower surface of the other end of the bimetallic strip element is provided with a semicircular contact;

step three, preparing a polymer PTC element:

the polymer PTC element is prepared by processes of pressing, irradiating, cutting and the like of a conductive polymer sheet and metal foils attached to the upper surface and the lower surface of the conductive polymer sheet, wherein the conductive polymer sheet is formed by mixing a polymer material and conductive powder to form a sheet, and the polymer material is one or a mixture of more of polyethylene, polyvinylidene fluoride, polyvinyl chloride, polypropylene, polystyrene, nylon, polycarbonate, polyurethane, polytetrafluoroethylene, polyethylene terephthalate and the like; the conductive powder is selected from: one or more of metal nitride, metal powder, carbon black powder, metal carbide, metal boride and metal silicide; the polymer PTC element can be purchased to manufacture a polymer PTC chip according to performance requirements and size requirements;

the upper surface of the polymer PTC element is connected with the connecting end of a No. 1 common pin terminal, and the other surface of the connecting end is provided with an NO contact; the lower surface of the polymer PTC element is connected with a connecting surface of a No. 3 pin terminal, the area of the connecting surface is larger than that of the lower surface of the polymer PTC element, the excessive part is bent downwards to form a bent part, a boss is arranged on the bent part, and the bent part is connected with the No. 2 pin terminal and the connecting end of the bimetallic strip element and is clamped and fixed by the boss;

step four, assembling:

extending the leading-out end of the No. 1 common pin terminal out of the cutting groove of the insulating base to enable the leading-out end to be at the same side as the leading-out end of the No. 2 common pin terminal, wherein the No. 1 common pin terminal is connected with the upper surface of the polymer PTC element in the cutting groove; the portion of bending of No. 3 pin terminals pushes away to the link of No. 2 pin terminals, inlay in the recess of the link of No. 2 pin terminals to the boss of the portion of bending, make the link of No. 2 pin terminals fully contact with No. 3 pin terminals after, with the semicircle type contact on the bimetallic strip component with NO contact connection, each part after the assembly is accomplished packs into in the shell, the temperature sensitive PTC protector that makes, with 1 number sharing pin terminal and No. 2 pin terminals draw forth the end and be connected to the circuit that needs the protection.

The invention provides a brand new protection scheme for protecting the low-current motor and the vehicle-mounted motor in the household appliance. When the motor has locked-rotor current suddenly increased, the temperature of a motor coil rises, the bimetallic strip element part is protected preferentially, the NO contact is opened, and the circuit is cut off; meanwhile, the macromolecule PTC element is partially connected into the circuit to start working, and the bimetallic strip element can continuously present an off state by self heat; only when the power supply is turned off, the polymer PTC element part does not work, and the bimetallic strip element can be contacted again when the temperature is reduced to the rated temperature, so that the initial state is recovered. The invention can effectively avoid the repeated 'open-close' state of the temperature control device during long-term work, thereby avoiding the generation of the phenomenon of electric arc discharge. The invention has the double functions of over-temperature protection and power failure recovery of the existing protector.

Drawings

FIG. 1 is a front view of the present invention;

FIG. 2 is a top view of the present invention;

FIG. 3 is an overall view of the present invention;

FIG. 4 is an assembly schematic of the present invention;

the reference numbers in the figures illustrate:

1-insulating base; 11-grooving;

2-a bimetallic element; 4-semicircular contact;

no. 3-1 common pin terminal; 10-NO contact;

5-No. 2 pin terminal; 51-a groove;

no. 6-3 pin terminals; 61-bending part of No. 3 pin terminal; 611-boss;

7-polymer PTC element; 8-outer shell.

Detailed Description

As shown in fig. 1 to 4, a temperature-sensitive PTC protector comprises a housing 8, a metal pin terminal and a polymer PTC element 7 having upper and lower surfaces, wherein in the housing 8, the polymer PTC element 7 and a bimetal element 2 are connected in parallel and supported by an insulating base 1, the insulating base 1 fixes the pin terminal of the bimetal element 2 and the polymer PTC element, and the bimetal element 2 and the polymer PTC element 7 have a common pin terminal. In this embodiment, a temperature-sensitive PTC protector includes:

an insulating base 1 provided with a cutting groove 11;

a polymer PTC element 7 having an upper surface and a lower surface, fixed in the slot 11, the upper surface connected to the lower surface of the No. 1 common pin terminal 3, the upper surface of the No. 1 common pin terminal 3 having a NO contact, the leading end of the No. 1 common pin terminal 3 extending out of the housing 8 from the slot 11; the lower surface of the polymer PTC element 7 is connected with a No. 3 pin terminal 6;

the bimetallic strip element 2 forms a fixed end and a movable end through a No. 2 pin terminal 5 fixed on the insulating base 1, and a semicircular contact 4 is arranged at the movable end, corresponds to the NO contact 4 arranged on the upper surface of the No. 1 common pin terminal 3 as shown in figure 1, and is set to be in a two-contact normally-closed state; as shown in fig. 1 and 2, the lead-out terminal of pin terminal No. 2 5 protrudes out of housing 8 on the same side as the lead-out terminal of pin terminal No. 1 common pin terminal 3, as shown in fig. 2 and 3; the inner side of the No. 2 pin terminal 5 is connected with the No. 3 pin terminal 6, so that the polymer PTC element 7 and the bimetallic strip element 2 are connected in parallel;

and a housing 8, the above components being assembled in the housing 8, the leading-out ends of the No. 1 common pin terminal 3 and the No. 2 pin terminal 5 extending out of the housing 8 at the same side.

As shown in fig. 1 and 4, in this embodiment, the No. 3 pin terminal 6 has a downward bent portion 61, and the bent portion is provided with a boss 611; the bottom surface of the connection end of the pin terminal No. 2 5 is provided with a groove 51, and the boss 611 is clamped in the groove 51.

The temperature-sensitive PTC protector of this embodiment is prepared by the following steps:

step one, preparing an insulating base 1:

the insulating base 1 is made of a temperature-resistant insulating material, an insulating high polymer material with the melting temperature of more than or equal to 145 ℃ can be made into a base by a pouring or molding process, an independent cutting groove 11 is processed on the base, and the No. 2 pin terminal 5 is directly fixed on the insulating base 1 by injection molding or the No. 2 pin terminal 5 is fixed on the insulating base 1 by welding, as shown in figures 2 to 4, the leading-out end of the No. 2 pin terminal 5 extends out of the insulating base 1;

step two, preparing the bimetallic strip element 2:

as shown in fig. 1 and 4, two ends of two metal sheets with different thermal expansion coefficients in the bimetal element 2 are fixedly connected after being overlapped, one end of the bimetal element 2 is fixed at the connecting end of the No. 2 pin terminal 5, and the lower surface of the other end is provided with a semicircular contact 4;

step three, preparing a polymer PTC element 7;

the polymer PTC element 7 is prepared by processes of pressing, irradiating, cutting and the like of a conductive polymer sheet and metal foils attached to the upper surface and the lower surface of the conductive polymer sheet, wherein the conductive polymer sheet is formed by mixing a polymer material and conductive powder to form a sheet, and the polymer material is one or a mixture of more of polyethylene, polyvinylidene fluoride, polyvinyl chloride, polypropylene, polystyrene, nylon, polycarbonate, polyurethane, polytetrafluoroethylene, polyethylene terephthalate and the like; the conductive powder is selected from: one or more of metal nitride, metal powder, carbon black powder, metal carbide, metal boride and metal silicide; the polymer PTC element 7 can be purchased to manufacture a polymer PTC chip according to performance requirements and size requirements;

as shown in fig. 1, the connection end of the No. 1 common pin terminal 3 is connected to the upper surface of the polymer PTC element 7, and an NO contact 10 is provided on the other surface of the connection end; the lower surface of the polymer PTC element 7 is connected to the connection surface of the No. 3 pin terminal 6, the area of the connection surface is larger than that of the lower surface of the polymer PTC element 7, and the extra part is bent downwards to form a bent part 61, as shown in fig. 4, the bent part 61 is designed to be conveniently connected to the connection end of the No. 2 pin terminal 3 of the bimetallic strip element 2, and a boss 611 is arranged on the bent part 61;

step four, assembling:

extending the leading end of the No. 1 common pin terminal 3 out of the cutting groove 11 of the insulating base 1 to enable the leading end to be at the same side as the leading end of the No. 2 pin terminal 5, wherein the No. 1 common pin terminal 3 is connected with the upper surface of the polymer PTC element 7 in the cutting groove 11; the No. 3 pin terminal 6 is connected with the lower surface of the polymer PTC element 7; the bending part 61 of the pin terminal No. 3 6 is pushed to the connecting end of the pin terminal No. 2 5, so that the bending part 61 of the pin terminal No. 3 is in contact connection with the pin terminal No. 2; the semi-circular contact 4 on the bimetallic strip element 2 is in contact connection with the NO contact 10, and the dynamic contact and the static contact are in a normally closed state; the No. 1 common pin terminal 3 is a common leading-out pin of the bimetallic strip element 2 and the macromolecule PTC element 7, all parts after assembly are arranged in the shell 8, and the leading-out ends of the No. 1 common pin terminal 3 and the No. 2 common pin terminal 5 are connected to a circuit needing protection.

In this embodiment, the bimetal element 2 and the polymer PTC element 7 are located in the same space.

In this embodiment, No. 2 pin terminal 5 is at the inboard fluting 21 of insulating base 1, and No. 3 pin terminal 6 bends the junction and has set up boss 611 simultaneously, has made things convenient for both to connect.

The output ends of the No. 1 common pin terminal 3 and the No. 2 common pin terminal 5 can be set to be different sides according to different installation requirements.

The temperature-sensitive PTC protector can select proper polymer PTC elements according to the requirements of the environment temperature, the protection time and the like. The bimetallic strip element 2 with different resistance values can be formed according to different materials, or the required bimetallic strip element 2 can be selected, the bounce temperature of the bimetallic strip element can be properly adjusted in the process, and the bimetallic strip element 2 with various specifications can be formed.

The working principle of the invention when used as a protector for motors is as follows: when the motor has a locked-rotor current surge, the temperature of a motor coil rises, the bimetallic strip element 2 acts preferentially, the semicircular contact 4 and the NO contact 10 are opened, and the circuit is cut off; meanwhile, the macromolecule PTC element 7 heats itself when the switch-in circuit starts working, and provides heat for the inner space of the protector continuously, so that the temperature in the shell 8 is kept higher than the recovery temperature of the bimetallic strip element 2, and the bimetallic strip element 2 is always in an action state. Only when the power supply is turned off, the polymer PTC element 7 in the protector does not work any more, and when the temperature is reduced to the rated temperature, the movable contact and the static contact of the bimetallic strip element 2 can be switched on again, and the initial state is recovered.

Claims

1. A temperature-sensitive PTC protector, comprising a shell, a pin terminal and a polymer PTC element with upper and lower surfaces, characterized in that the polymer PTC element and the bimetal element in the shell are connected in parallel and supported by an insulating base The insulating base fixes the pin terminals of the bimetal element and the polymer PTC element, and the bimetal element and the polymer PTC element have a common pin terminal.

2 . The temperature-sensitive PTC protector according to claim 1 , wherein the insulating base is provided with a slot, and the polymer PTC element is installed in the slot. 3 .

3. The temperature-sensitive PTC protector according to claim 1 or 2, characterized in that: the upper surface of the polymer PTC element is connected to the lower surface of one end of the shared pin terminal; There is a NO contact, which corresponds to the position of the semi-circular contact set at one end of the bimetal element, and makes the two contacts in a long-closed state; the other end of the shared pin terminal is drawn out of the casing through the slot of the insulating base The lower surface of the polymer PTC element is provided with another pin terminal, the pin terminal is connected with the pin terminal of the bimetal element, so that the polymer PTC element and the bimetal element are in a parallel structure.

4. temperature-sensitive PTC protector according to claim 3, it is characterized in that: described common pin terminal is No. 1 pin terminal, and the pin terminal of bimetal element is fixed in place as No. 2 pin terminal. On the insulating base, the leading end of the No. 1 pin terminal protrudes out of the casing through the slot, and the other end is connected with the upper surface of the polymer PTC element, and the other side is provided with a NO contact, which is connected with one end of the bimetal element. The positions of the set semicircular contacts correspond; the other end of the bimetal element is connected with the No. 2 pin terminal; at the same time, the lower surface of the polymer PTC element is provided with a No. 3 pin terminal, and the No. 3 pin terminal is Connect with the No. 2 pin terminal, so that the polymer PTC element and the bimetal element have a parallel structure.

5 . The temperature-sensitive PTC protector according to claim 4 , wherein the No. 2 pin terminal is injection-molded on the insulating base. 6 .

6. The temperature-sensitive PTC protector according to claim 4, characterized in that: the No. 2 pin terminal has a groove on the inside of the insulating base, and meanwhile, the No. 3 pin terminal is provided with a bending connection, and in the A boss is arranged at the bending connection, and the boss is embedded in the groove.

7 . The temperature-sensitive PTC protector according to claim 4 , wherein the output terminals of the No. 1 pin terminal and the No. 2 pin terminal are on the same side or different sides. 8 .

8. temperature sensitive PTC protector according to claim 4 is characterized in that: comprise:

an insulating base provided with a slot;

A polymer PTC element has an upper surface and a lower surface, which are installed in the slot and fixed, the upper surface is connected to the lower surface of the No. 1 common pin terminal, the upper surface of the No. 1 common pin terminal is provided with NO contacts, and the No. 1 common pin terminal The leading end of the pin terminal protrudes from the slot; the lower surface of the polymer PTC element is connected to the No. 3 pin terminal;

A bimetal element, a fixed end and a movable end are formed by the No. 2 pin terminal fixed on the insulating base, and there is a semi-circular contact at the movable end, which shares the NO contact position set on the upper surface of the No. 1 pin terminal Correspondingly; the leading end of the No. 2 pin terminal extends out of the shell and is on the same side as the leading end of the No. 1 shared pin terminal; the inside of the No. 2 pin terminal is connected to the No. 3 pin terminal, so that the polymer PTC element and the bimetallic sheet are connected. components are connected in parallel;

A shell, the above-mentioned components are assembled in the shell, and the lead-out ends of the No. 1 shared pin terminal and the No. 2 pin terminal protrude out of the shell on the same side.

9 . The temperature-sensitive PTC protector according to claim 1 or 2 , wherein the insulating base is an insulating base with a melting temperature of not lower than 145° C. 10 .

10 . The temperature-sensitive PTC protector according to claim 1 or 2 , wherein the bimetal element and the polymer PTC element are located in the same space in the casing. 11 .

11. a preparation method of temperature-sensitive PTC protector according to claim 8, comprising the steps:

Step 1, the preparation of the insulating base:

The insulating base is made of temperature-resistant insulating material, and the insulating polymer material with a melting temperature of ≥145°C is prepared into a base by a casting or molding process. Fix the No. 2 pin terminal on the insulating base or fix the No. 2 pin terminal on the insulating base by welding, so that the lead end of the No. 2 pin terminal extends out of the base;

The second step is to prepare a bimetal element. Two metal sheets with different thermal expansion coefficients are superimposed and the two ends are connected and fixed to form a bimetal element. One end of the bimetal element is fixed at the connection end of the No. 2 pin terminal, and the other end is fixed. The lower surface is provided with semi-circular contacts;

Step 3, the preparation of polymer PTC element;

The polymer PTC element is prepared by the process of pressing, irradiating, and cutting a conductive polymer sheet and metal foil attached to the upper and lower surfaces, wherein the conductive polymer sheet is a mixture of polymer material and conductive powder. The polymer material is selected from polyethylene, polyvinylidene fluoride, polyvinyl chloride, polypropylene, polystyrene, nylon, polycarbonate, polyurethane, polytetrafluoroethylene, polyterephthalic acid One or more mixtures of ethylene glycol esters, etc.; the conductive powder is selected from one of metal nitrides, metal powders, carbon black powders, metal carbides, metal borides, and metal silicides. One or several mixtures; polymer PTC components can also purchase finished polymer PTC chips according to performance needs and size requirements;

Connect the connecting end of No. 1 shared pin terminal on the upper surface of the polymer PTC element, and set a NO contact on the other side of the connecting end; connect the connecting surface of the No. 3 pin terminal on the lower surface of the polymer PTC element, The area of the connection surface is larger than the lower surface of the polymer PTC element, and the excess part is bent downward to form a bent part, and a boss is arranged on the bent part, and the bent part is connected to the No. 2 pin terminal and the bimetal The connection ends of the sheet elements are connected and fixed by the bosses;

Step four, assembly:

Extend the leading end of the No. 1 shared pin terminal from the slot of the insulating base so that it is on the same side as the leading end of the No. 2 pin terminal. The No. 1 shared pin terminal is connected to the polymer PTC in the slot. The upper surface of the component is connected; the bending part of the No. 3 pin terminal is pushed to the connecting end of the No. 2 pin terminal, and the boss to the bending part is embedded in the groove of the connecting end of the No. 2 pin terminal, so that the No. After the connection end of the pin terminal is fully contacted with the No. 3 pin terminal, the semi-circular contact on the bimetal element is contacted and connected with the NO contact. Protector, connect the terminals of No. 1 shared pin terminal and No. 2 pin terminal to the circuit that needs to be protected.