GB2157084A

GB2157084A - Diverting overvoltages in telephone switching systems

Info

Publication number: GB2157084A
Application number: GB8507203A
Authority: GB
Inventors: Helmut Schmider
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1984-03-31
Filing date: 1985-03-20
Publication date: 1985-10-16
Also published as: GB8507203D0; ES285739U; ES285739Y; GB2157084B; DE3412130A1; DE3412130C2

Abstract

In an arrangement for diverting overvoltages, applicable to telephone switching systems, all overvoltage arresters (7) of the switching equipment are combined on plug-in printed board assemblies (2). In each assembly (2), the ground terminals of all overvoltage arresters (7) are connected to a contact (3) mounted in the lower front corner of the assembly (2). A portion of this contact (3) projects beyond the edge of the assembly (2) and has two contact fingers pointing in the direction of insertion. During insertion of the assembly (2) into the subrack, the contact (3) contacts a grounded bus bar (4) attached to a horizontal bar (8) of the subrack. <IMAGE>

Description

SPECIFICATION Telephone switching systems This invention relates to telephone switching systems and in particular to an arrangement for diverting overvoltages from assemblies pluggable into subracks in a telephone switching system.

Telephone switching equipment must be protected from overvoltages which are caused by damage to cables or by lightning, which arrive over the external lines and which may destroy the switching equipment. Protection is conventionally provided by overvoltage arresters which are disposed, for example, at the main distribution frame of an exchange and are thus connected ahead of the switching equipment in special racks. The overvoltage arresters are frequently accommodated in plugs which are inserted into sockets in the distri bution frames. Such an arrangement is disclosed, for example, in DE-AS 26 42 779, where a multi pole plug contains two overvoltage arresters for the two speaking wires. DE-OS 27 06 681 shows a similar design in which plugs containing arresters can be inserted into a disconnecting strip provided with a base.

In private branch exchanges, the overvoltage arresters are directly associated with the switching equipment, i.e., they are mounted on printed board assemblies containing the switching devices. As each overvoltage arrester requires a connection to ground, it is necessary with this arrangement to provide ground contacts in all connectors of the assemblies, as well as associated ground wires.

An object of the invention is to provide a simpler overvoltage protection arrangement for telephone switching systems wherein the overvoltages are diverted over a path separate from the signal lines.

According to one aspect of the invention an ar rangement for diverting overvoltages from assem blies pluggable into subracks in a telephone switching system is characterised in that all overvoltage arresters of the switching equipment are mounted on special printed board assemblies, and that each of the assemblies is provided, in one of its front corners, with a contact which, when the assembly has been inserted, is in contact with a grounded bus bar extending over the entire width of the subrack. This arrangement dispenses with the need for special plugs. All overvoltage arresters are combined on plug-in assemblies from which overvoltages are diverted through one contact per assembly to a grounded bus bar.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a partial perspective view of several asssemblies which have been inserted in a subrack and are connected to a bus bar in accordance with the invention, and Figure 2 is an enlarged side view of one of the assemblies of Figure 1.

The drawings show printed board assemblies 2 equipped with overvoltage arresters 7, as are needed in telephone systems. Several such assemblies 2 are inserted in one of the usual subracks of, e.g. a rack or a cabinet, of which only a lower horizontal bar 8 fitted on its top with guide rails 9 for the assemblies can be seen in Figure 1. A bar 4 of L-shaped section is attached to the front of the horizontal bar 8 in such a way that its free leg points toward the front. This bar 4 forms the bus bar for the entire subrack and is grounded via a cable 10 at the side of the rack.

Each of the assemblies 2 has in its lower front corner a contact 3 which is soldered to the printed conductors (not visible) leading to the ground terminals of all overvoltage arresters 7. The contact 3 projects downwardly beyond the lower edge of the assembly 2 and has two forked contact fingers 5 which point in the direction of insertion and are provided at their free ends with noses 6 directed toward each other, which can be seen especially clearly in Figure 2. During insertion of the assembly 2 into the subrack, these contact fingers 5 move onto the free leg of the bus bar 4 until this leg is between the noses 6 of the contact fingers 5.

Since the distance between the noses 6 is smaller than the thickness of the bus bar 4, good contact making is ensured.

It is readily possible to mount the contacts in the upper front corners of the assemblies if the bus bar is attached to an upper horizontal bar of the subrack (not shown).

Claims

1. An arrangement for diverting overvoltages from assemblies pluggable into subracks in a telephone switching system, characterised in that all overvoltage arresters (7) of the switching equipment are mounted on special printed board assemblies (1), and that each of the assemblies (1) is provided, in one of its front corners, with a contact (3) which, when the assembly has been inserted, is in contact with a grounded bus bar (4) extending over the entire width of the subrack.

2. An arrangement as claimed in claim 1, characterised in that the contact (3) is soldered to the conductors of the printed board assembly and has a portion projecting beyond one of the longitudinal edges of the assembly and having two contact fingers (5) which point in the direction of insertion and whose free ends are provided with noses (6) directed toward each other.

3. An arrangement as claimed in claim 2, characterised in that the bus bar (4) has an L-shaped cross-section, and that its free leg lies between the contact fingers (5) of the contacts (3) of the assemblies (1).

4. An arrangement for diverting overvoltages from assemblies pluggable into subracks in a telephone switching system substantially as described with reference to the accompanying drawings.