plessey2.gif (5108 bytes)PLESSEY Telephone Nl250A


CB Motorway
All-weather Telephone

This motorway telephone is based on the All weather instrument which has been extensively proved in situations calling for the utmost reliability and robustness. It is used on British and Australian motorways and offers the advantages of simple operation, durability with light weight, competitive cost, low maintenance liability and high quality transmission.

Supplied to the Dept. of the Environment (United Kingdom) as their 'Tele. 350' and the Australian Post Office permit No. C/72/31/22

Construction
The use of materials liable to corrosion is avoided. The enclosure, consisting of a base, a body and a hinged door, is of corrosion-resistant aluminium alloy; other parts are of brass, phosphor-bronze and high-quality stainless steel. The body is a robust aluminium-alloy casting, webbed to form a solid internal shelf for the handset. Two screws inside the body secure it to the base. This is of hard aluminium alloy and recessed in the body. It mounts all the circuit components.

The self-closing door- another aluminium-alloy casting - is equipped with spring-loaded brass hinges, a magnetic catch, and a stainless-steel grab handle. The door projects beyond the case side, allowing it to be knocked open if iced up. It is channelled to mate with the rim of the body, so that foamed Neoprene in the channel excludes moisture when the door is shut. Similar seals are provided between the body and base, and between the body and the post mounting adapter. Th is adapter accepts a 2in (51mm) diameter post.

In the parked position of the handset the receiver rests on a stainless steel cradle plate, the earpiece operating the internal cradle switch via a plunger. A bracket inside the lid prevents the handset being dislodged by vibration. To assist replacement of the handset at night the front compartment is painted white, and a self-energised light source is provided just below the cradle plate. This source, which is encased in clear plastic, has a useful life in excess of 20 years.

The recessing of the front compartment affords a degree of weather protection, particularly to the cradle switch plunger, even with the lid open. The rear of the telephone baseplate carries two 4in (102mm) stainless-steel bell gongs, actuated via a rocking shaft passing through a weatherproof sleeve to the interior of the body.

The post-mounting adapter affords complete protection to the rear of the telephone while still allowing an adequate calling signal. The adapter carries a 2-way terminal block having screw connections for the pin-ended leads from the telephone.

Installation and Maintenance
The telephone readily separates from the post mounting adapter by means of socket screws at the rear of the adapter. This allows the adapter to be separately mounted on the post and positively secured by two set screws in the adapter spigot. After terminating the cable all that is necessary is to screw the telephone connections into the terminating block and re-attach the telephone to the adapter.

Maintenance is facilitated by the telephone body being separated from the base. After releasing the body fixing screws the door is closed to protect the handset, and the body lifted down to hang suspended from the base by the nylon cord provided. Thus all components and wires are accessible.

Components and Finish
Components of proven reliability are used throughout. The circuit is the BPO approved Type 706B and the ringer is based on the BPO Type 59A incorporating a ceramic magnet. A 27 way terminal block moulded in glass-filled nylon is provided for terminations inside the telephone. The handset, with temperature resistant coiled cord, is moulded in high-impact plastic.

Apparatus finishes are suitable for the tropics, and connecting wires are insulated with PVC, which is impervious to moisture and not subject to mould growth or insect attack.

The standard external finish is a bright yellow epoxy resin stove enamel, but other colours can be supplied to quantity order.

Post-mounting adapter
The full size handset silhouette is displayed on both the front of the telephone door and on the rear of the post-mounting adapter, and is in black on a rectangular panel of high-reflectivity yellow-beaded material.

Dimensions (including adapter)
Height 16.5in (413mm)
Max. width 6in (152mm)
Depth (including handle) 9in (229 mm)

Weights (approx.)
Telephone (net) 10.5lb (4.77kg)
Post-mounting adapter (net) 41lb (1 .9 5 kg)

Motorway All Weather Telephone Nl250A with post-mounting adapter N 200134A

PUBLICATION No.7411, 1975

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Last revised: April 06, 2000