GB2308510A - Plug with safety cut-out switch - Google Patents

Abstract

An electrical plug (1) comprises a first movable electrically conductive contact and a second fixed, electrically conductive contact (42). The movable contact is carried by a bimetallic member (43) and is arranged such that in a datum position (not shown), the first movable contact rests in contact with the fixed contact so that electrical current can pass therebetween, and in the event of an excessively large current, the bimetallic member is deformed so as to remove the movable contact from the fixed contact, thereby to break the connection therebetween. Either a removable obstruction (45) prevents return of the bimetallic strip (figure 3) or a push-button (46) causes return of a bistable bimetallic strip.

Description

A PLUG WITH SECURITY DEVICE The present invention relates to a plug with security device, and more particularly to a plug including a security device disposed between at least one conductive insertion plate and one conductive wire of the plug.

When an excessively large current passes through an electric appliance, the security device automatically opens the circuit so as to protect the electric appliance and ensure safety.

Conventionally, a current-limiter such as a fuse or a disconnector is added to a circuit to shut off the current in the case of excessively large current. With respect to the fuse, once it is burned down, a new one must be replaced therefor. It is quite inconvenient for the user to replace the fuse so that the use of the fuse has been gradually reduced. With respect to the disconnector, the structure thereof is relatively complicated and the price thereof is higher. Therefore, it is uneconomic to use the disconnector and it is difficult to install the disconnector on the circuit.

As a result, it happens frequently that several circuits with smaller current specification commonly use one disconnector with larger current specification so as to save the cost and facilitate the installation. However, such disconnector will inevitably have a relatively low sensitivity.

A conventional plug has several conductive insertion plates at front end (the number of which is determined by the power source pattern) and several corresponding conductive wires at rear end connected with the insertion plates in a housing respectively. In use, the insertion plates are inserted into a power socket which supplies power to the electric appliance. According to such arrangement, the plug is equipped with no protective or security device. Therefore, in case the electric appliance such abnormally works that the disconnector cannot be operated to shut off the current, an excessively large current may still pass through the electric appliance to damage the same or even cause danger. As a result, the safety in using electricity cannot be ensured and accidents still take place frequently.

According to one aspect of the present invention therefore there is provided a plug comprising a security device connected between at least one conductive insertion plate and one conductive wire of the plug. The security device may include a thermal bimetal blade, a movable contact disposed on the bimetal blade and a fixed contact naturally contacting with the movable contact.

When an excessively large current passes through the electric appliance, the bimetal plate is bent to separate the movable contact from the fixed contact and automatically open the circuit so as to shut off the current and avoid burning down of the electric appliance or accident.

In a different aspect of the present invention, when the movable contact is separated from the fixed contact, an insulative separating board may be inserted into a space between the movable and fixed contacts so as to keep the circuit open. After the malfunction is eliminated, a lever arm may be depressed to push the separating board away from the space, permitting the movable contact to contact with the fixed contact again so as to re-close the circuit. While having a more accurate operation, the structure of the plug is simple and the cost thereof is lower.

In another aspect of the invention, the plug may comprise a housing, several conductive insertion plates adapted to be inserted into a power socket, conductive wires connected to an electric appliance and a security device, the insertion plates being respectively connected with the conductive wires in the housing; said plug being characterised in that the security device is disposed between at least one insertion plate and one conductive wire and the security device includes a casing and a disconnector seat disposed therein, a thermal bimetal blade being disposed on the disconnector seat and connected with the insertion plate, the bimetal blade having two lateral portions integrally associated with each other at front ends and a middle rearward extending resilient plate, a movable contact being disposed at a rear end of the resilient plate, a fixed contact being disposed on the disconnector seat and connected with the conductive wire, the movable contact naturally contacting with the fixed contact, a bent portion being formed at front end of the bimetal blade, whereby when an excessively large current passes through the electric appliance, the bimetal plate is bent to separate the movable contact from the fixed contact and by means of the bent portion, the bimetal blade is kept bent and prevented from restoring to its original shape so as the keep the circuit open.

A restoring button may be disposed beside the movable contact and depressable to make the bimetal blade restore to its original shape and make the movable contact contact with the fixed contact for re-closing the circuit. Said restoring button may be restored to its home position by a resilient member disposed in the casing.

In some embodiments, a filler may be filled into a space between the casing and the housing.

In yet another aspect of the invention, the plug may comprise a housing, several conductive insertion plates adapted to be inserted into a power socket, conductive wires connected to an electric appliance and a security device, the insertion plates being respectively connected with the conductive wires in the housing, said plug being characterised in that the security device is disposed between at least one insertion plate and one conductive wire and the security device includes a casing, a disconnector seat disposed therein, a thermal bimetal blade disposed on the disconnector seat, a movable contact disposed on the bimetal blade, a fixed contact disposed in the casing and connected with the conductive wire to naturally contact with the movable contact, and an insulative separating structure, whereby when an excessively large current passes through the electric appliance, the bimetal plate is bent to separate the movable contact from the fixed contact and open the circuit, the insulative separating structure being simultaneously inserted into a space between the movable and fixed contacts so as to keep the circuit open.

Said bimetal blade may have two lateral portions integrally associated with each other at front ends and a middle rearward extending resilient plate, and the movable contact may be disposed at a rear end of the resilient plate.

In some embodiments, the separating structure may include a support seat disposed in the casing to support a lever arm which has one end extending out of the housing, an insulative separating board being linked with the lever arm and disposed beside the movable and fixed contacts.

The separating board may be forced by an extension spring to extend into the space between the two contacts so as to keep the circuit open and ensure safety.

Following is a description by way of example only with reference to the accompanying drawings of methods by which the present invention may be performed.

In the drawings: Figure 1 is a perspective view of a first embodiment of the present invention; Figures 2 and 3 are side sectional views of the first embodiment according to Figure 1; Figures 4 and 5 are top sectional view of the first embodiment according to Figure 1; Figure 6 is a side sectional view of a second embodiment of the present invention; Figure 6A is an enlarged view showing the bimetal blade of the second embodiment according to Figure 6; and Figure 7 is a side sectional view of the second embodiment, showing that a bimetal blade is bent to separate a movable contact from a fixed contact.

Please refer to Figures 1 to 5. According to a first embodiment of the present invention, the plug of the present invention includes a housing 1, a pair of conductive insertion plates 2, conductive wires 3 and security device 4. The insertion plates 2 are respectively connected with the conductive wires 3 in the housing 1. The security device 4 is disposed between at least one insertion plate 2 and one conductive wire 3.

The security device 4 includes a casing 47 and a disconnector seat 41 disposed therein. A thermal bimetal blade 43 is disposed on the disconnector seat 41 and connected with the insertion plate 2. The bimetal blade 43 has two lateral portions integrally associated with each other at front ends and a middle resilient plate 441. A movable contact 44 is disposed at a rear end of the resilient plate 441. A fixed contact 42 is disposed in the casing 47 and connected with the conductive wire 3. The movable contact 44 naturally contacts with the fixed contact 42. A support seat 452 is disposed in the casing 47 to support a lever arm 451 which has one end extending out of the housing. The other end of the lever arm 451 is disposed with an insulative separating board 45 extending to one side of the two contacts. An extension spring 453 is disposed on a rear side of the separating board 45. In normally used state, the current flows from the socket to one of the insertion plates 2 through one of the wires 3 into an electric appliance and then flows from the electric appliance through the fixed contact 42, movable contact 44 and the bimetal blade 43 back to the socket.

In abnormally working state and when an excessively large current passes through the plug, the thermal bimetal blade 43 is bent due to the high temperature caused by the large current. At this time, the resilient plate 441 is displaced to make the movable contact 44 separate from the fixed contact 42 so as to open the circuit.

Simultaneously, the separating board 45 is forced by the extension spring 453 to extend into a space between the two contacts. Therefore, the movable contact 43 is kept separated from the fixed contact 44 so as to ensure safety. Also, the lever arm 451 protrudes outside the housing 1. After the malfunction of the electric appliance is eliminated, the lever arm 451 is depressed to slide the separating board 45 out of the space between the contacts back to its home position. On the other hand, the bimetal blade 43 is restored to its original shape due to lack of current and thus the resilient plate 441 drives and restores the movable contact 44 to contact with the fixed contact 42 for normal use.

Figures 6 and 7 show a second embodiment of the present invention, wherein a disconnector seat 41 is disposed between at least one insertion plate 2 and one conductive wire 3. The disconnector seat 41 is disposed with a fixed contact 42. A thermal bimetal blade 43 is disposed under the fixed contact 42. The bimetal blade 43 has two lateral portions and a middle resilient plate 441. A bent portion 47 is formed at front end of the bimetal blade 43 and the resilient plate rearward extends from the bent portion 47 between the two lateral portion. A movable contact 44 is disposed at rear end of the resilient plate 441 to contact with the fixed contact 42.

When an excessively large current passes through the electric appliance, the bimetal plate 43 is bent to separate the movable contact 44 from the fixed contact 42. At this time, by means of the bent portion 47, the bimetal blade 43 is kept bent and prevented from restoring to its original shape. Therefore, the circuit is kept open. After the malfunction is eliminated, a restoring button 46 is depressed to make the bimetal blade 43 restore to its original shape for normal use.

The restoring button 46 is restored to its home position by a compression spring 461.

In conclusion, the plug with security device of the present invention is able to prevent abnormal current from passing through an electric appliance so as to ensure safety and avoid accident.

The above description and drawings are only used to illustrate some preferred embodiments of the present invention, not intended to limit the scope thereof. Many modifications can be made without departing from the spirit of the present invention.

Claims (8)

1. An electrical connector, particularly a plug, comprising a first movable electrically conductive connecting member, and a second fixed, electrically conductive connecting member; wherein the movable member is carried by a bimetallic member, which bimetallic member is arranged such that in a datum position, the first movable member rests in contact with the fixed member so that electrical current can pass therebetween, and in the event of an excessively large current, the bimetallic member is deformed so as to remove the movable member from the fixed member, thereby to break the connection therebetween; and wherein detent means are provided to maintain the movable member in the removed position.

2. An electrical connector as claimed in claim 1, wherein said bimetallic member is configured such that it is conformationally stable in the removed position, and selectively operable returning means are provided for returning the bimetallic strip to the datum position from the removed position.

3. An electrical connector as claimed in claim 2, wherein the bimetallic member comprises two spaced, substantially parallel elongate parts, a bridge part connecting the two elongate parts at or towards one end thereof, and a plate part connected to the bridge part and interjacent the two elongate parts, which plate part carries the movable member thereon; and wherein the bridge part is bent such that the bimetallic member is confomationally stable in a removed configuration in which the movable member is spaced from the fixed member.

4. An electrical connector as claimed in claim 3, wherein the selectively operable returning means comprises a push rod for pushing against the bimetallic member so as to return it to the datum position from the removed configuration.

5. An electrical connector as claimed in claim 1, wherein said detent means comprises a movable electrically insulating member, urging means for urging the insulating member to move between the first and second members, and selectively operable withdrawing means for withdrawing the insulating member from between the first and second members, the arrangement being such that in the event of an excessively large current, the first member is removed from the second member, thereby allowing the insulating member to move between the first and second members so as to hold the first member in the removed position.

6. An electrical connector as claimed in claim 5, wherein the urging means comprises a spring.

7. An electrical connector as claimed in claim 5 or claim 6, wherein the withdrawing means comprises a manually operable lever which is connected to the insulating member.

8. An electrical connector, particularly a plug, substantially as hereinbefore described with reference to and as shown in Figures 1 to 5 or Figures 6 and 7 of the accompanying drawings.