EP0072125B1

EP0072125B1 - Fuse holder

Info

Publication number: EP0072125B1
Application number: EP19820303880
Authority: EP
Inventors: Tetsuro Ikeda
Original assignee: ECHO ELECTRIC Co Ltd
Current assignee: ECHO ELECTRIC Co Ltd
Priority date: 1981-07-22
Filing date: 1982-07-22
Publication date: 1988-10-05
Also published as: EP0072125A2; JPS616608Y2; DE3279092D1; EP0072125A3; JPS5814656U

Description

The present invention relates to a fuse holder for a cartridge type fuse.
Fuse holders are used in household electric applicances such as TV sets, stereo sets and so forth, as well as in various industrial equipment. In recent years there have been remarkable improvements and development in the field of electronic parts such as switches, followed by improvement in the performance of fuses. Also the applications for and use of fuses is spreading year by year. Under these circumstances, there is an increasing demand for a fuse holder having enhanced safety and improved performance.
As shown in Figure 1, a typical conventional fuse holder has a metallic screw member 4 provided with an external thread 4a. A clamp 3 clamping one end of the fuse 5 is secured to the screw member 4. The screw member 4 in turn is fixed to a cap 1 made of plastics. The fuse holder further has a generally cylindrical socket 2 made of plastics. A terminal 7 fitted in the open end of the internal bore of the socket 2 has an internal thread 7a for engagement with the external thread 4a of the screw member 4. Another terminal 8 is disposed at the closed end of the internal bore of the socket 2. In mounting the fuse, the fuse 5, which is clamped at its one end by the clamp 3, is inserted into the internal bore of the socket 2, and the cap 1 is rotated by fingers to screw the screw member 4 into the terminal 7 so that the external thread 4a of the screw member 4 and the internal thread 7a of the terminal 7 engage with each other to drive the screw member 4 deeper into the bore of the socket 2 until the inner end of the fuse 5 is stopped by the terminal 8. In this state, the two terminals 7 and 8 are electrically connected to each other through the fuse 5. The socket 2 is shown attached to a panel 11 by means of a washer 9 and spring ring 10 or the like.
This known fuse holder has the following drawback. Namely, in the course of mounting of the fuse, the screw member attached to the cap 1 is brought into contact with the internal thread 7a of the terminal 7, i.e. electrically connected to the terminal 7. In this state, the major part of the screw member 4 is still exposed to the outside of the socket. lf the terminal 7 has an applied voltage therefore the operator may receive an electrical shock when his finger happens to contact with the screw member 4.
CH-A-442494, DE-A-1588940 and GB-A-1086629 disclose fuse holders having sockets which are capable of preventing access to conductive parts of the fuse holder from outside and thus deal with the above problem. CH-A-442494 has a fuse holder which comprises an outer sheath of insulating material that surrounds a fuse retainer and is of a length such that when the fuse and sheath are inserted into a socket, when or before a first end of the fuse comes into contact with a slide terminal in the socket, the end of the sheath that is opposite to the first end of the fuse reaches the open end of the socket and prevents access to any conductive parts of the fuse or holder from outside. However, the specification discloses that the cap has to be screwed onto the end of the socket which, of course, is troublesome to an operator. In DE-A-1588940 notches are defined at the periphery of a circular hole in a flat portion of a cap-shaped conductor and tabs engage with the notches in order to retain the cap on the socket, with the result that the diameter of the conductor is larger than it needs to be and thus occupies more space. The Swiss and German specifications disclose a metallic cylindrical member coaxially secured within a socket and integrally formed with a side terminal.
According to the invention there is provided a fuse holder having a cap with a fuse retainer for retaining one end of a fuse;

a socket for the fuse having a side terminal and an end terminal, the cap being adapted to be connected to the socket to provide an electrical connection between the side terminal and the end terminal through the fuse;
an outer sheath of an insulating material surrounding the fuse retainer, of a length such that when the fuse and the cap are inserted into the socket, when or before the other end of the fuse comes into contact with the side terminal in the socket, the end of the outer sheath reaches the open end of the socket to prevent access to any conductive part of the fuse or holder from outside;
a cylindrically formed metallic case included in the fuse retainer, provided with latch tabs formed at the open end thereof; and
a metallic cylindrical member, coaxially secured within the socket, integrally formed with the side terminal; characterized in that: the metallic cylindrical member is formed with L-shaped notches at one end thereof for receiving the latch tabs to secure the cap in the socket; and that the fuse retainer further includes:
a semi-cylindrically formed retainer lug within the metallic case for retaining the fuse at one end thereof, the retainer lug having U-shaped legs at the other end thereof;
a coil spring secured in the retainer lug, the coil spring having an end supported by the U-shaped legs, the fuse being held in use between the coil spring and the end terminal; and
a second coil spring disposed between the fuse retainer and the outer sheath and compressed by engagement with the end of the cylindrical member, to bias the cap outwardly of the socket even when the fuse is absent within the fuse holder.
Such a fuse holder completely eliminates the chance of contact of the operator's finger with electrically live portions of the fuse holder during mounting of the fuse in the fuse holder and there is also provided a fuse holder which permits an easy detaching of the cap from the socket even when there is no fuse in the fuse holder.

One example of a fuse holder constructed in accordance with the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a sectional side elevational view of a typical known fuse holder;
Figure 2a is a sectional side elevational view of a cap incorporated in a fuse holder according to the invention;
Figure 2b is a sectional side elevational view of a socket incorporated in the fuse holder of the invention;
Figure 3a is a partly cut-away perspective view of a fuse retainer of the fuse holder of the example, showing the internal structure of the fuse retainer;
Figure 3b is a perspective view of a cylindrical metallic member integrated with a side terminal;
Figure 4a is a front elevational view of the fuse holder and inserted retainer;
Figure 4b is a rear elevational view of the fuse holder and inserted retainer;
Figure 4c is a side elevational view of the fuse holder and retainer.

In the drawings the same reference numerals are used to denote the same parts as those in the known fuse holder explained before, and detailed explanation of such parts is omitted.
Referring first to Figure 2a, a cap 1 has a groove 1a adapted to receive a screwdriver or the peripheral edge of a coin or the like for inserting the cap 1. The cap 1 also has an internal recess 1 b. An outer sheath 1c, made of an electrically insulating material, is formed integrally with the cap 1 or, alternatively, made separately from the cap 1 and then bonded to the latter by means of an adhesive. Since this insulating outer sheath surrounds a fuse retainer 20 as will be discussed later, accidental touching of the fuse retainer 20 by a user's fingers is completely prevented.
Referring now to Figure 2b, the socket 2 has a through hole 2a formed in a lateral side portion thereof. A side terminal 7 integral with a cylindrical member 15 (see Figure 3b) is extended to the outside of the socket 2 through the hole 2a. An end hole 2b is formed in the end portion of the socket 2. An end terminal 8, which is connected to an end contact 8a for contacting one end of the fuse 5, is extended to the outside of the socket 2 through the hole 2b. Since the metallic ring 15 is disposed deep in the socket 2, it cannot be touched easily even if a finger is inserted partially into the end opening 2c of the socket 2. As shown in Figure 3b, L-shaped notches 15a are formed in one of the rims of the cylindrical member. These L-shaped notches 15a are adapted to engage with latch tabs 12a,12a provided on the metallic case 12. The end terminal 8 has an end projection 16.
As will be clearly understood from Figure 3a the fuse retainer 20 accommodates a coil spring 13 and a retainer lug 14 which is provided with substantially U-shaped legs 14a. The retainer lug 14 is fixed to the bottom wall of a metallic case 12 with one end of the legs 14a secured to the bottom wall of the fuse retainer 20. The coil spring 13 is fixed at one end between the legs 14a and the retainer lug 14, so that it can never come out of the case 12. The case 12 has two latch tabs 12a arranged at 180° apart at the open end 12b thereof, although it can have three latch tabs arranged at 120° or four latch tabs arranged at 90° if desired. In such cases, needless to say, it is necessary to form three or four L-shaped notches 15a at the rim of the cylindrical metallic member 15 in the socket 2 at 120° or 90° so as to correspond to the latch tabs 12a. The combination of the latch tabs 12a and the L-shaped notches 15a is known as a swan type latch mechanism. The invention, however, does not exclude the use of other type of fixing such as an Edison screw or other bayonet type latch. In addition, the cap 1 has a coiled spring 18 between the metallic case 12 and the other sheath 1c of the cap 1.
The fuse holder is used in the following manner:-

First of all, one end of the fuse 5 is brought up to the opening 12b of the metallic case 12 in the cap 1. Then the end of the fuse 5 is inserted into the case 12, surrounded by the outer sheath 1c, such that the inserted end of the fuse 5 is embraced and retained by the retainer lug 14, with the inner end surface of the fuse 5 contacted by one end of the coil spring 13. The operator then holds the cap 1 by his fingers and inserts the other end of the fuse 5 into the end opening 2c of the socket 2 which is mounted on a panel, chassis or the like, until the other end of the fuse 5 comes into contact with the end contact 8a in the socket 2. To explain the setting of the fuse in the socket 2 in more detail, representing the distance between the end of the outer sheath 1 of the cap 1 and the terminal and more remote from the cap by 1₁ and the distance between the open rim 15b of the member 15 and the open end 2c of the socket 2 by 1₂, I, is less than or equal to I₂. Therefore, when the other terminal reaches the position of the open rim 15b of the member 15, the peripheral edge of the end of the outer sheath 1c of the cap 1 has been received already by the open end 2c of the socket 2. If a voltage is applied to the cylindrical metallic member 15 during installation of the fuse, conductive parts such as the metallic case 12 in the cap 1 are electrically live as the other end of the fuse is brought into contact with the opening rim 15b of the cylindrical metallic member 15. However, the possibility of electric shock is completely eliminated because the outer sheath 1c surrounds the conductive member to keep fingers away from any live conductive parts.

The fuse 5 is inserted into the socket 2 until the latch tabs 12a of the case 12 are received by the L-shaped notches 15a of the member 15. In this state, the cap 1 is pressed in by fingers or, alternatively, by means of a screw driver or a coin received in the groove 1a of the cap 1. In consequence, the case 12 is moved deeper into the socket 2 while the one end terminal of the fuse 5 is moved deeper into the case 12 compressing the coiled spring 13. As a result, the cap 1 retaining the fuse 5 is completely received in the socket 2 and, at the same time, the latch tabs 12a reach the corners of the corresponding L-shaped notches 15a of the member 15. Then, the cap 1 is rotated to slide the latch tabs 12a along the bottom edges of the L-shaped notches 15a to complete the latching.
The reverse procedure to that described above is used for detaching the fuse 5. The latch tabs 12a are easily disengaged from the L-shaped notches 15a as the cap 1 is rotated in the reverse direction, so that the cap 1 is sprung out, together with the fuse 5, of the socket by the force of the compressed coil springs 13 and 18. Thus it is possible to take out the fuse in quite an easy manner.
When the cap 1 is inserted into the socket 2 without setting the fuse 5 therein, the spring 18 is engaged and compressed by engagement with the end of the opening 15b of the member 15. Therefore, the cap 1 can be forced out by the force of the spring 18.ft is thus possible to easilytake out the cap 1 even when there is no fuse set in the cap 1.

Claims

1. A fuse holder having a cap (1) with a fuse retainer (20) for retaining one end of a fuse (5);

a socket (2) forthe fuse having a side terminal (7) and an end terminal (8), the cap (1) being adapted to be connected to the socket (2) to provide an electrical connection between the side terminal (7) and the end terminal (8) through the fuse (5);

an outer sheath (1c) of an insulating material surrounding the fuse retainer (20), of a length such that when the fuse (5) and the cap (1) are inserted into the socket (2), when or before the other end of the fuse (5) comes into contact with the side terminal (7) in the socket (2), the end of the outer sheath (1c) reaches the open end (2c) of the socket to prevent access to any conductive part of the fuse or holder from outside;

a cylindrically formed metallic case (12) included in the fuse retainer (20), provided with latch tabs (12a) formed at the open end (12b) thereof; and,

a metallic cylindrical member (15), coaxially secured within the socket (2), integrally formed with the side terminal (7); characterized in that:

the metallic cylindrical member is formed with L-shaped notches (15a) at one end (15b) thereof for receiving the latch tabs (12a) to secure the cap (1) in the socket (2); and that the fuse retainer (20) further includes;

a semi-cylindrically formed retainer lug (14) within the metallic case (12) for retaining the fuse (5) at one end thereof, the retainer lug (14) having U-shaped legs (14a) at the other end thereof; a coil spring (13) secured in the retainer lug (14), the coil spring having an end supported by the U-shaped legs (14a), the fuse (5) being held in use between the coil spring (13) and the end terminal (8); and

a second coil spring (18) disposed between the fuse retainer (20) and the outer sheath (1c) and compressed by engagement with the end (15b) of the cylindrical member (15), to bias the cap (1) outwardly of the socket (2) even when the fuse (5) is absent within the fuse holder.