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 13 in. x 7 in. x 9 in. 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:-

1. On subscribers ccts.  connected to C.B., Auto., C.B.S. Nos. 2 and 3, & Magneto exchanges, and also on P.M.B.X.'s and P.A.B.X.'s.
2. On private-wires with generator signalling.
3. On private-wires with D.C. signalling, using the telephone in conjunction with “Unit, Signalling, No.6".
4. 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, Auto., S. S. No. 10 LA" is not suitable, a "Dial, Auto. , 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 Auto. subscribers' instruments.

4. Circuit

(a) The connexions are shown on Dgm. N 354;  a copy of each of the three panels is fixed inside the lid.

(b) A "Key No.303A" (with three plungers), arranged as per Fig. 2, Panel 3, Dgm. N 4301, provides switching according to requirements.

(c) "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
Dgm. N 354 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.