1. Field of the Invention
This invention relates to central office protector modules which provide a visual alarm indication when either of the incoming telephone lines protected by the module are shorted to ground and more particularly to the supplying of power to the modules and the appearance of the alarm indication also at a location remote to the module.
2. Description of the Prior Art
Central office protector modules which provide a visual indication of the mechanical type when either of the lines protected by the module are shortened due to a sustained overcurrent are known. One example of such a module is that disclosed in U.S. Pat. No. 3,587,021 entitled "Line Protector For A Communications Circuit" which issued on June 22, 1971 and is assigned to the same assignee as is the present invention. The module disclosed therein includes an alarm pin which is connected to ground when a sustained overcurrent condition grounds either of the two lines protected by the module. The '021 patent indicates that the grounding of the alarm pin can be used to close a circuit in the central office such that an external audible or electric lamp alarm device can be energized.
A module of the type disclosed in the '021 patent is the type R1104B module sold by assignee's Reliable Electric/Utility Products operating unit. That module plugs into a type 700 connector also sold by that same operating unit. Typically, a number of those connectors each holding a multiplicity of such modules are mounted on a single frame. An electrical lamp, i.e., a bulb, can be mounted on the frame to provide a visual indication that one of the multiplicity of the modules in that frame has connected its alarm pin to ground, i.e. closed the alarm circuit. The power for lighting the lamp is provided from the central office battery, typically -48 V. Wiring all of the alarm pins of all of the modules in the frame together provides a single wire which can then be wired to one side of the lamp. The other side of the lamp is wired to the battery. The connection to ground by the occurrence of a sustained overcurrent condition of at least one module alarm pin in the frame closes the circuit to the lamp. Current then flows from the battery to light the lamp.
There has been increasing demand by telephone operating companies for a central office module which provides a visual indication not only when the module connects at least one of the two lines it is protecting to ground as a result of a sustained overcurrent, but also as a result of a sustained overvoltage. There has also been increased interest that the visual indication be in the form of a light which is part of the module. Such a light has the advantage over a mechanical type indicator of the '021 module of being easily visible not only when the office is not that well lit, but also in a well lit office which may have several hundred or more connectors each holding up to 100 modules arranged in a multiplicity of racks. In a module which has its own visual indication in the form of a light included as part of the module, it is necessary to provide power to each module. It is advantageous and safer to provide such power in the form of a relatively low amplitude voltage rather than at the central office battery voltage. It is desirable that the system for providing such power include on the power supply a visual indication of a module failure and a means for testing that indicator. It is also desirable that the system include provision for an indication of module failure at a location remote from the power supply. It is further desirable that such a system allow each of the connector blocks in a given rack to be isolated one at a time so that the number of modules which have failed on that block can be determined.