Abstract
This Bureau of Mines handbook covers the installation, maintenance, and inspection of telephone systems in underground coal mines and provides guidelines for the inspection and optimum use of mine pager phones. Various interconnection schemes and wiring distribution systems are discussed, along with such precautions as mounting and connection of cabling to provide strain relief and drip loops. Battery requirements and means of determining minimum useful battery voltage are reviewed. The problems and recommended practices for protecting pager phone equipment against such transients as lightning are discussed. The parameters affecting wire-size selections are discussed, including recommendations for insulation and construction of cable, including twisted-pair, figure-eight, and solid-conductor versus multiconductor wire. Instructions and examples of minimum wire-size requirements for a variety of telephone and system configurations are provided. The preferred methods of cable splicing for branching and repairs are identified and discussed. Internal self-testing of pager phone circuits involved using the pager phone to verify its own operational readiness, including operation of the talk circuits, page circuits, and listen circuits. Local measurement of battery condition and remote measurement of battery status are described.
