A master socket is a panel at the point where the telephone company's wiring enters the wall. On one side of the socket, the wiring is the phone company's responsibility, and it must pay for any necessary service and repairs. On the other, the tenant is responsible. This arrangement is common to telephone companies in many regions of the world, but the term “master socket” and accompanying specific technology are primarily associated with British Telecom.
When phone service is ordered at a new structure, the phone company will install wiring and a master socket. The configuration has varied throughout the years. Historically, the socket had a single flat faceplate, and the wiring inside belonged to the phone company while the customer plugged into sockets at the front. More modern arrangements have a fixed upper faceplate and a movable bottom portion. This allows tenants to work on the wiring within part of the socket to set up extensions, DSL features, and other things.
Some master sockets come with DSL filtration built in. This can improve the quality of a DSL signal, even when customers are not actively using extensions. This is more common in modern sockets, which may be installed this way by default in case a house decides to order DSL service. In other cases, consumers can set up their own filters, or can hire a phone technician to install them if they are not comfortable with the wiring.
Within the master socket, several features distinguish it from other sockets that may be located elsewhere in the structure. One feature is the capacitor for the ringer tone, and another is voltage protection to limit damage from voltage spikes. It also has fittings for remote testing and sensing. Even if a line is not active, the phone company can run tests through it in preparation for starting service or to troubleshoot a problem.
Phone customers who contact the phone company for assistance with a problem may be asked a series of questions by a technician to determine whether the problem is within the structure or on the outside. A representative of the phone company can test the master socket and lines and provide information about the problem. If the issue is inside the structure, customers can select a repair person to address the issue. Sometimes phone problems are simple, and tenants may be able to solve them with the assistance of diagrams and step-by-step guides, available online at do-it-yourself repair sites.