GB2143685A

GB2143685A - Retainer for a surge arrester in a terminal box

Info

Publication number: GB2143685A
Application number: GB08411330A
Authority: GB
Inventors: Kazutoshi Nakao
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-07-15
Filing date: 1984-05-03
Publication date: 1985-02-13
Also published as: GB8411330D0; JPS6019174U; GB2143685B

Abstract

In a terminal box (3) (particularly pole-mounted) housing at least one surge arrester (8) and having at least one terminal (4) connected to an external sensing circuit, and at least one earthed support plate (7) to support the surge arrester(s), a metal retainer is provided for the or each surge arrester (8) in the form of an electrically conductive spring strip (1), connected at one end to the terminal (4) and having a contact portion (6) at the other end, the strip being flexed intermediate its ends so as to retain the arrester (8) against the support plate (7) by spring pressure with the contact portion (6) spaced from the plate (7), and to be released from its stressed position when the arrester (8) is removed so as to bring the contact portion (6) into contact with the earthed plate (7) and thus complete a circuit for the external sensing circuit to indicate the absence of the arrester (8). <IMAGE>

Description

SPECIFICATION Retainer for a surge arrester in a terminal box The present invention relates to a retainer for use with a surge arrester installed in a terminal box which may be mounted on a pole, particularly for telephone lines and to a terminal box using such a retainer.

Surge arresters are usually provided in electronic telephone equipment to allow surge current caused by a light discharge to flow directly to the ground, and thereby to avoid any possible damage to or destruction of such electronic equipment which might be caused by the flow of surge current.

However, it has hitherto been impossible for the central exchange to detect if an arrester is actually connected to the telephone line electronic equipment, since the absence of such an arrester has no effect on the functioning of the telephone line itself.

Visual inspection has been the only way of assuring the presence of arresters. When a large number of telephone lines is involved, the absence of arresters for some of the lines may be overlooked, and in such a case, lightning discharge can cause interruption of the telephone service and, in bad cases, danger to telephone subscribers can result.

In orderto prevent the trouble in question, previously known arresters have been provided with a switch for ensuring connection of the arrester.

However, this adds to the cost, and at the same time, a relatively large terminal box, for example, will be required to receive the arresters, depending on the number of such arresters used in the terminal box.

It is an object of the present invention to eliminate the above disadvantages associated with the previously known arrangements by providing a novel retainer for holding an arrester in a terminal box (which may be mounted on a pole) by means of which the presence or absence of the arrester may be ascertained.

According to one aspect of the present invention, there is provided a terminal box (preferably of the polemounted type) having at least one terminal electrically connected to an external sensing circuit, at least one earthed support plate adapted to support a surge arrester thereon, and a metal retainer comprising an electrically conductive spring strip flexed intermediate the ends thereof for resiliently retaining the arrester against said support plate, said spring strip having at one end thereof means of which it is connected to said terminal and having a contact portion at the other end thereof extending toward said support plate, said contact portion being spaced from said support plate when said spring strip is resiliently stressed to retain said arrester against said support plate, the arrangement being such that when said arrester is removed from said support plate, said spring strip is released from its stressed position and thereby causes said contact portion to abut against said support plate so that a circuit to earth is completed for the external sensing circuit to sense the removal of said arrester from the space between said spring strip and said support plate.

In this way, the absence of an arrester can be readily detected, thus making it possible to take steps to prevent any possible damage to or destruc -tion of electronic instruments, and danger to tele phone subscribers or others which may be caused by a lightning discharge.

According to another aspect of the invention, a retainer for use in such a terminal box comprises an electrically conductive spring strip flexible intermediate its ends, means at one end of said strip for connecting said strip in use to one said terminal and contact means formed at the other end of said strip for electrically contacting said strip in use to said support plate when said retainer is not supporting a surge arrester thereon.

The invention will now be further described with reference to the drawings, in which: Figure 1 is a schematic front view of one form of retainer according to the present invention; Figure 2 is a schematic underneath plan view of the retainer of Figure 1; Figure 3 is a schematic left-hand end view of the retainer of Figure 1; Figure 4 is a partially cut-away schematic front view of a pole mounted terminal box illustrating the mounting of the retainer according to Figures 1 to 3 therein; Figure 5 is a partially cut-away schematic top plan view of the terminal box of Figure 4; and Figure 6 is a schematic partial front view of the terminal box of Figure 4 to illustrate the mounting of an arrester by the retainer of the present invention.

Referring now to the drawings, there is shown a retainer 1 according to the present invention. As may be seen from Figures 4to 6, the retainer 1 is intended for use in a conventional terminal box 3 of the type mounted on a pole and including a plurality of terminals 4, nuts 5 and earthed support plates 7 for supporting a plurality of surge arresters 8. Therefore, the terminal box 3 as illustrated thus includes a plurality of retainers, depending on the number of terminals and arresters to be employed. For clarity, however, reference will hereinafter be made only to one retainer 1.

The retainer 1 is formed from a longitudinal strip of an electrically conductive spring material, such as a phosphor bronze strip, and is bent to a special configuration as generally shown in Figure 1. The retainer 1 has adjacent one end thereof a first generally horizontal portion in which is provided a mounted aperture 2 (Figure 2), by means of which the retainer 1 is fitted over the terminal 4 through the mounting aperture 2 and is secured by the nut 5. The retainer 1 also has at the other end thereof, a contact portion 6 which is bent into a semi-circular configuration. The retainer 1 is mounted on the terminal box 3 in such a way that the contact portion 6 is resiliently pressed against a conductive support plate 7 mounted in the terminal box 3 opposite to the terminal 4 and is adapted to support an arrester 8 in co-operation with the retainer 1, as shown in Figure 6.In this state, the retainer is practically earthed through the support plate 7 that serves as an earth terminal (Figure 6).

Referring more specifically to Figure 1,the retainer 1 is bent and folded intermediate the ends thereof so as to obtain sufficient force and flexibility to hold the arrester 8 against the support plate 7 as in Figure 6.

The retainer 1 has adjacent the folded portion thereof a projection 9 adapted to abut against the arrester 8 and thereby effectively to press the arrester 8 against the support plate 7. The retainer 1 further has adjacent the contact portion 6, a second generally horizontal (considered when in use) portion or abutment portion 10 for receiving the end of the arrester 8. In use, the arrester 8 is inserted from the top of the terminal box 3 into the space between the retainer 1 and the support plate 7 so as to be held in a press-fitting manner. The abutment portion 10 serves to prevent possible downward slipping of the arrester 8 due to vibrations or similar external forces.

The operation of the retainer thus formed is as follows. Should any of the retainers mounted in the terminal box 3 fail to retain any arrester 8, the retainer 1 in question is earthed as it is pressed at the contact portion 6 thereof against the plate 7 which forms the earth terminal. From this earthed position of the retainer, the central telephone exchange can readily sense the absence of the arrester 8 through, for example, a lead wire (not shown) connected in common to each terminal 4. Conversely, when each of the retainers 1 resiliently holds an arrester 8 against the plate 7, as shown in Figure 6, the contact portion 6 is held away from the plate 7 to keep all contacts open, and consequently, the lead wire is not earthed. Thus, by means of a suitable sensing circuit, the central telephone exchange can readily check that all the arresters 8 being pressed by the retainers 1 are present, and the absence of any arrester is immediately indicated.

Claims

1. Aterminal box having at least one terminal electrically connected to an external sensing circuit, at least one earthed support plate adapted to support a surge arrester thereon, and a metal retainer comprising an electrically conductive spring strip flexed intermediate the ends thereof for resiliently retaining the arrester against said support plate, said spring strip having at one end thereof means by which it is connected to said terminal and having a contact portion at the other end thereof extending toward said support plate, said contact portion being spaced from said support plate when said spring strip is resiliently stressed to retain said arrester against said support plate, the arrangement being such that when said arrester is removed from said support plate, said spring strip is released from its stressed position and thereby causes said contact portion to abut against said support plate so that a circuit to earth is completed for the external sensing circuit to sense the removal of said arresterfrom the space between said spring strip and said support plate.

2. A terminal box according to claim 1 which is mounted on a pole.

3. A terminal box as claimed in claim 1 having a plurality of terminals commonly connected to said external sensing circuit, each said terminal being connected to a respective retainer for a respective surge arrester.

4. A terminal box substantially as hereinbefore described with reference to and as illustrated in Figures 4 to 6 of the drawings.

5. A retainer for use in a terminal box as claimed in claim 1 comprising an electrically conductive spring strip flexible intermediate its ends, means at one end of said strip for connecting said strip in use to one said terminal and contact means formed at the other end of said strip for electrically contacting said strip in use to said support plate when said retainer is not supporting a surge arrester thereon.

6. A retainer for use in a terminal box as claimed in claim 1, substantially as hereinbefore described with reference to and as shown in Figures 1 to 3 of the drawings.