For use as the first socket-outlet on a direct exchange line or PABX line. They contain surge protectors (for line protection against electrical surges) and capacitors. Wiring regulation restrictions. Any number of sockets may be installed thereafter, with a maximum of 5 telephones. normally being allowed on one exchange line. Commercial installations: Our telephone sockets are suitable in all situations after the PBX/PABX . For key systems and other ‘special’ systems, the manufacturer’s instructions should be referred to.Telephone sockets should not be installed into the same fixing or mounting boxes as mains rated cable. The XTF professional quality pre-filtered telephone socket, descrete filtration with maximum compatibility & performance. The XTF pre-filtered socket contains the same high quality filter as our highly respected XF-1e. Containing four high quality ferrite cores to ensure that accurate frequency separation is achieved. The XTF comes in two standard sizes 85mm & 68mm and can be used to replace an existing telephone socket or add a new extension.