TELEPHONE No. 254

P.O. ENGINEERING DEPT.
ENGINEERING INSTRUCTIONS
TELEPHONES
STATIONS
A3919
Issue 2, 8.9.47

TELEPHONE No. 254
PORTABLE TELEPHONE FOR 4-WIRE AND 2-WIRE WORKING

1. General
Telephone No.254 was introduced for use by engineering staff in the provision of private wires for the Services and for cases of emergency; it will now be retained for use by the engineering staff in providing temporary speaker facilities in special cases, e.g. 'setting-up' operations on new cable routes where the normal speaker facilities are not available.

2. Description
The telephone consists of a standard "Telephone No. 394LB", together with a generator and subsidiary items, mounted in a wooden case 13in. x 7in. x 9in. The case is provided with a carrying handle and is fitted with sliding-back flap hinges, so that the lid may be removed, if required. It is necessary to open the lid fully to give access for operating the telephone.

3. Facilities
The Telephone No. 254 provides the following facilities:-

(a) 4-wire working. For terminating 4-wire private-wires with generator-signalling over the phantom or (using the telephone in conjunction with "Unit, Signalling, No. 6") for terminating 4-wire private wires with D. C. signalling.

(b) 2-wire working. For use on 2-wire circuits as follows:-

On subscribers circuits connected to C.B., Automatic, C.B.S. Nos. 2 and 3, & Magneto exchanges, and also on P.M.B.X.'s and P.A.B.X.'s.
On private-wires with generator signalling.
On private-wires with D.C. signalling, using the telephone in conjunction with a 'Unit, Signalling, No.6'.
On trunk and junction terminations with generator signalling.

Stock provision of Telephone No. 254 has not been arranged to cater for exchange areas requiring dials of S, B, or W type. If a "Dial, Automatic, S. S. No. 10 LA" is not suitable, a "Dial, Automatic, S. S. No. 10" for the area concerned should be requisitioned and fitted locally.

(c) 2-wire working, with battery, feed to line. For feeding transmitter current to line for C. B. or Automatic subscribers' instruments.

4. Circuit

The connexions are shown on Diagram N354; a copy of each of the three panels is fixed inside the lid.
A "Key No.303A" (with three plungers), arranged as per Fig. 2, Panel 3, Diagram N 4301, provides switching according to requirements.
"Coils, Retardation, No. 3402" are arranged to give access to the phantom of the 4-wire circuit for signalling purposes.

5. Method of connecting the Telephone
Diagram N354 shows the method of connecting the telephone for all of the conditions referred to in par.3.

6. Requisitions
Including maintenance-exchange requisitions, should circulate through the normal channels.