RELAY-SWITCH No. 3000 - 4000 TYPE

Introduced soon after 1936, these relay-switches are cased in cast iron with two interlocking covers for customer premises use or steel with a single cover for exchange use. The purpose of this relay-switch is to isolate low voltage telephony circuits from mains voltages.

The units consist of a 3000 type relay and up to two 15amp mercury switches (Tubes, Mercury. No. 1). These tubes can be Make, Break or Change-over actions (the make and break function are dependant on the angle by which the tubes are fixed). Where only one mercury tube is fitted, a Tube, Mercury, No. 1, Dummy is fitted in the spare position. The relay has a standard Change-over contact (pt) fitted but not wired.

Mercury tubes were used as they did not spark or wear out. They were also sealed and did not react to the surrounding air.

The relay and any additional components are fitted in the lower partition. The extra components are generally used when the relay is operated from a low voltage AC source, such as ringing current.

Nowadays a flashing lamp can all be done with discrete electrical components - click here for more information.

Safety Warning
The glass tubes have the metal Mercury in them. This is a dangerous liquid chemical and medical attention should be sought if any contact is made with ANY part of the human body. Never break a tube and always wear disposable gloves.

Title Description
There are numerous variations of the Relay-Switches and each is described by the title number.

The title number is interpreted as follows:-

Name - Type - locking (L) or non-locking (NL) - quantity and rating of mercury tubes
relay cover type

e.g. RELAY-SWITCH No. 3106 N.L. 1-15 AW - this describes a Relay-Switch, 3106 type, which is non-locking and includes one Tube, Mercury rated at 15amp and the unit is fitted with an AW cover.

Types Available

Relay-Switch Title No.	Relay No.	Tube Action	Fitted with	Use
3101 NL 1-15AX	3101	1M		70v DC
3101 NL 2-15 AX	3101	2M		70v DC
3102 L 1-15 AW	3102	1M		70v DC
3102 NL 1-15 AX	3102	1M		70v DC
3102 NL 2-15 AW	3102	2M		70v DC
3103 NL 2-15AX	3101	2M		70v DC
3104 NL 1-15 AW	3203	1M		70v DC
3106 L 1-15 AW	4309	1M		70v DC
3106 NL 1-15 AW	4309	1M		70v DC
3201 L 1-15 AW	3102	1M	Rectifier No. 1/12A	Operated by 50c/s AC ringing
3201 NL 1-15 AW	3102	1M	Rectifier No. 1/12A	Operated by 50c/s AC ringing
3301 NL 1-6 AP or AR		1M		Exchange use - 50v DC
3301 NL 2-6 AP or AR		2M		Exchange use - 50v DC
3401 NL 1-15	3201	1B or 2B	Rectifier No. 1/12A & Capacitor M.C. No. 102	Operated by 50c/s AC ringing
3503 NL 2-15 AX	3102	2M	Rectifier No. 1/12A & 3 x Resistor, Coils	DC mains 250v
3601 NL 2-30 BA	4514	1C or 2C	Uses Tubes, Mercury No. 4 (30 amps)	Exchange use - 50v DC
4001 NL 1-15 AX	3102	1B or 2B		70v DC
4001 NL 2-15 AX	3102	1B or 2B		70v DC

Covers
Relay Cover AW - Used in subscribers premises - cast iron casing.
Relay Cover AX - Used in exchanges - steel casing.

Operation
The unit is separated into two compartments by a partition across the middle. This partition has a sliding rod through it, which is operated by the relay armature. The relay is located in the lower compartment. The other side of the relay armature operates a standard contact set. The rod, when the relay is energised, moves upwards pushing a spring loaded lever, in the upper compartment, upwards. The end of the lever is located in a swinging arm which holds the mercury tubes. The swinging arm rotates and the mercury in the tubes cover the contacts, making an electrical circuit.

In the non-locking version, when the relay is de-energised, the spring in the upper compartment assists in restoring the swinging arm back to it's home position.

Drawings
Relay Cover AW - 62064
Relay Cover AX - 62065
Relay-Switch 3100 to 3900 AW assembly - 62066
Relay-Switch 3100 to 3900 AX assembly - 62067
Relay-Switch 3100 to 3900 AW arrangements - TP631
Tubes, Mercury No. 1 - CD240

The upper section is where the high voltage mains cables enter the unit and are terminated.		The lower section section are where the low voltage telephony cables enter the unit and are terminated. The relay and other components are fitted this section.
	AW type The picture above is dated 1938. This is a Siemens made Relay-Switch unit with two mercury tubes. It had two cast covers, one to cover the mains section and one to cover the telephony section. The steel partition in the middle segregates the two sections.


	AX type Used in exchanges with no cast iron container. A simple steel cover was fitted. This one is fitted with a single mercury tube.