10 + 100
Lamp Signalling
with Automatic or C.B. exchange lines

n376.jpg (22547 bytes)This switchboard employs lamp signalling on all circuits, and is arranged with positive supervision on all calls. Each board has capacity for 10 exchange and 100 extension lines with 15 cord circuits. For installations of from 100 to 200 extensions, two units may be bolted together to form a two-position, non-multiple switchboard. For such application, each unit is equipped with longer connecting cords and double pulley weights.

Exchange lines are normally for connection to an automatic exchange, but alternatively can be C.B. Each cord circuit has a speak/ring key and a dial/ring-back key.


  1. Through dialling and clearing.
  2. Automatic exchange-line hold.
  3. Separate positive supervision on local calls: double positive supervision on exchange calls.
  4. Visual ringing indication.
  5. Ring back.
  6. Visual and audible fuse alarm.
  7. Audible alarm.
  8. Panel pilot signal.
  9. Cord test.

Night-service working on cord circuits 1 to 11.

Note. Additional plug-ended through-cords to connect extra circuits for night-service working can be supplied.

A welded, pressed-steel frame with integral plinth forms the main structure and component mounting, and is enclosed with laminated-wood panels. These are surfaced with hard-wearing, buff-coloured plastic, edged and secured by metal trims finished in glossy elephant grey stove enamel. In contrast, the face panel is coloured black and the key shelf buff linette.

When units are installed en suite, adjacent intermediate side panels are removed and the frames bolted together. Similarly, the front panel below the key shelf and the rear door can both be removed for convenience of access.

The face panel has exchange and extension signalling lamps and associated jacks arranged in alternate rows. Provision is made for night-extension keys, fuse and night alarm keys and the cord-test jack.

The key shelf is arranged with supervisory lamps and switching keys for cord circuits and miscellaneous facilities.

Internal equipment is positioned and mounted for maximum accessibility. Incoming cables enter via covered apertures in the open constructed plinth, and terminate on soldered terminal fields at the bottom of the unit.

For convenience of handling (e.g. during installation) the hinged key shelf can be raised and its apron lowered to reduce the depth by 8!in (21 6mm).

Switching keys are of miniature type, the wedge-shaped ivory coloured handles being tipped in a contrasting colour, rendering operated keys instantly discernible.

Operating equipment, supplied as standard, includes a lightweight plug-in handset with capsule receiver, a manually operated ringing-current generator and a dial adjusted to transmit 10 pps with 2:1 break/make pulse ratio and with standard numbering, i.e. 1 to 0.

Alternative equipment, available in lieu of, or in addition to, includes a lightweight plug-in headset, a transistor ringing unit powered from a 24V source, and a dial with any desired numbering and adjustment.

Internal components, including relays and relay retards, are to British Post Office specifications, and are afforded tropical finish, i.e. with coils suitably impregnated and metal parts specially finished. Conductors are heavily insulated with p.v.c., giving protection against moisture, fire, attack by insects and fungoid growth. Connecting cords are additionally protected with p.v.c. sleeving and nylon braiding.

The switchboard operates on 24V d.c., the busy-hour current drain being approximately 2A. Power is normally derived from the local mains supply via a battery eliminator unit. Alternatively, batteries with charging equipment can be supplied if preferred.

Line Limits
Using Plesseyphones type N2020 (auto) or N1520 (C.B.) or Etelphones type N1900 (auto) or N1340 (C.B.) as extension instruments, the maximum permissible loop resistance between the public exchange and extension is 1000 ohms.

Height. 48in (1220mm)
Width. 30in (772mm)
Depth. 32in (813mm)

Weights (approx.)
3101b (140.8kg) net.

Plessey Publication No. 7138 (1970)

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Last revised: October 12, 2019