NTS LONDON 12
APPROVAL No. NS/2706/3/F/451321
This telephone system came in 4 varieties and the different variant can be identified by locating the system model number. The London 12M is shown to the right.
There was also an earlier London 12 which had a metal creamy/buff coloured all metal case. It came with a fixed configuration of 4 + 8 and was the original 'London' range PABX. It was LD only both internally and externally.
Could be configured to 2+10 or 3+9 with additional cable.
All versions have a RS 232/V24 call logging interface fitted as standard and are designed to work with 10pps loop disconnect telephones. MF versions will operate with either loop disconnect telephones (no recall button required) or with MF Timed break recall telephones (recall button required).
The system mains plug must be fused at 2 amps.
A protective earth must be provided - the system protective earth point must be connected to a proven building earth point.
Extensions 21, 22 and 23 are mains fail extensions. On system start up extension 21 is the master phone that is used for all system programming. This can be changed to another extension.
REN of each extension port is 3.
Maximum external wiring must not exceed 220 metres.
Maximum extension loop resistance is 42 ohms and all extensions are wired in a 2 wire star configuration with master sockets.
The DIP switches are located in the top right hand corner of the system, on the main circuit board with Switch 1 uppermost.
Switch 1 determines what kind of dialling is used for outgoing calls on each exchange line.
Line 4 is not approved in the UK.
Switch 2 defines whether or not MF receivers are fitted
Switch 3 determines the system size
The London 12M was also sold by Cass Electronics as Cass-Tel 12.
Last revised: December 21, 2010