|INTRINSICALLY SAFE SWITCHBOARDS
MAGNETO, CORD (30 to 100 Lines)
Certificate: T/TEL/2F (Methane)
These switchboards are primarily for use in collieries where 30 or more magneto extension lines are required.
They are intrinsically safe in methane when used with telephones or other equipment of certified type and powered from an approved source.
They are made in two sizes: one is a single-panel board having capacity for 50 lines; the other a two-panel board with capacity for 100 lines. The six stock equipment's available are listed in the table.
The strong hardwood case is matt polished. It has removable panels at the rear and below the keyshelf. The plugshelf is protected by red fibre.
Plug-restored disc indicators are used for calling, and push-button restored disc indicators for clearing, the latter being mounted in the keyshelf. The clearing signal is operated from either end of the line.
The operator's telephone circuit incorporated in the board includes the latest anti-side-tone feature, which ensures satisfactory reception even in noisy situations. A moulded plastic handset with plug connection is supplied as standard, but a head and breast set or a lightweight headset can be substituted if specified.
Other components include an 'alnico' generator, a key for ringing back on the answering cords, and another for switching into circuit an external night alarm bell of certified safe type, which should be ordered separately if required.
Batteries for the bell and transmitter circuits are supplied only when specified. They should not be fitted inside the board.
Wiring is always provided for the full complement of circuits, to facilitate the extension of partial equipment's. Provision is also made for the connection of power ringing, and terminals are included to enable code ringing delay equipment to be used with up to 15 lines on the smaller switchboard and 18 lines on the larger, but these can be increased in either case for any requirements up to the 50 line or 100 line capacity.
The switchboard Circuits
Line and clearing indicator coils are normally of 1,000 ohms resistance, but 250 ohm coils can be supplied if specified.
Auto-to-magneto switching equipment can be used with these switchboards. When units for more than 4 lines are required they can be fitted on a special wooden mounting on either side of the board.
Circuit schematic and wiring diagrams are supplied with each board.
Dimensions of Casework:-
Last revised: October 12, 2019