1000 type key list

1000 type keys contact layouts
1600, 1700 and 1800 assemblies -SD101 (Mark 1) and  SD131 (Mark 2).

ETL / Plessey
1000 type keys contact layouts:-
Single Lever - N9300 - N9900 - N24209, N24324
Double Lever - N95303MA1
Treble Lever - N95304MA1
Four Lever - N96790MA1

These keys are a miniaturised version of the standard lever key and are called the 1000 type.  Introduced in the late 1960's on new equipment and produced by ETL / Plessey.

The key mechanism is all plastic except for the mounting frame and the spring loaded lever saddle.

Contacts are mounted on both sides and are operated at the same time by a central lever mechanism.  The key can be in one of three positions and can be locking or non-locking in two positions.  The contacts are normal when the key is upright.  Keys can also be supplied that only have two positions.

The handle is held in place, on top of  two plastic formers, which are located on two metal pins (hidden under the handle) and which allow the handle to rock both ways.  The formers can also be supplied where they rock in one direction only.

The plastic formers rest on levers which operate the contacts.  The levers in turn rest on the central sprung loaded metal saddle and this keeps the whole mechanism under tension. 

The lower ends of the levers can be either angled or flat (or both).  An angled end will cause the key to lock when pushed in that direction, whilst a flat end will be non-locking (see single key picture below).

When operating these keys a handle should always by in place.  This ensures that the formers are held in place and stops them spreading outwards, due to the pressure of the spring.

These keys have been known to break in use.  Either the plastic spring holder fractures (replacement switch required) of the levers fall out (repairable).

The levers can be replaced but extreme care must be taken as they are under tension.

A method to replace the levers is as follows:-

  1. Replace the formers if damaged.

  2. Fit the formers onto the key frame making sure they are the correct sort and correctly located on the two pins.

  3. Replace the key top (important).

  4. Compress the spring loaded metal saddle on both sides, with pliers and insert a lever, holding the lever with another pair of long nosed pliers.

  5. Now compress the other side of the spring loaded saddle.  Whilst compressing it, hold the installed lever, upright and in place with your finger.

  6. Once compressed, insert the lever, holding the lever with a pair of long nosed pliers.


  • Small-frame keys with two sets of up to 12 springs per throw.

  • Large-frame keys with two sets of up to 24 springs per throw.

  • Small-frame keys with more than 12 and up to 24 springs. Single throw only.

  • Large-frame keys with more than 24 and up to 48 springs. Single throw only.

  • Longitudinal multiple units comprising two, three and four small-frame keys respectively.

Single                                                Large                                                                       Multiple

Switching Action
Keys are either single or double-throw with locking (L) and/or non-locking (N) actions.  A stop (S) action is provided for single-throw keys.

Contact Rating
Silver (suffixed MA)
300mA at 250Va.c. (r.m.s.)
100mA at 250V d.c.
300mA at 100V d.c.
Platinum (suffixed MC)
600mA at 250Va.c. (r.m.s.)
300mA at 250V d.c.
1.0A at 100V a.c. or d.c.

Note: Contact ratings given are for non-inductive loadings only.  Adequate spark quenching must be applied when connecting into inductive circuits.

Tag terminated and soldered.

Contact Units
Are in four categories: Make (M); Break (B); Changeover (C) and Make-before-break (K).
The 'changeover' unit can also serve as a 'make' or 'break' unit.

Uses Handles No. 18 which are available in various colours.  These handles can have coloured inserts in the top.  A linking handle can also be used to operate two keys simultaneously.  A single key locking handle is also available.

Spring Numbering
The chamfered end of the key denotes the start of the spring numbering.

Keys are designed to mount vertically with the keys chamfered end at the top.
Captive nuts allow the use of welded studs in lieu of fixing screws.
Minimum spacing between horizontal centres is 5/8in (16mm).

Single Key

Single Key Spring Numbering
Chamfered edge uppermost

Plessey N24209, N9300 and 9400

Plessey N9900


BACK Home page BT/GPO Telephones Search the Site Glossary of Telecom Terminology Quick Find All Telephone Systems

Last revised: February 27, 2023