The Lincolnshire Heritage Exchange

Key and Lamp Unit

Featured left the working 20 line Key & Lamp Unit on display in our exchange. the top row has a telephone associated with it and we have the bottom row connected to a headset and pullout dial.

There are two main components of the key and lamp unit, the desktop switch with a telephone or headset and the relay sets which are wall mounted in a central area.

The key and lamp unit comes in two sizes, ten lines or twenty lines.  The relay sets are made up of two types, the first one has the relays for five lines and additional relays that produce the timing.  For a five line system only the first relay set is needed, and the system is expandable in multiples of five by using the second type of relay set, one for each group a five lines

The system allows a telephone to have access to a maximum of twenty lines, and there is virtually no limit on the amount of stations that can be added to the system, although twenty positions would cover ever line.  This system was ideal in a sales environment where customers can be dealt with by a team of people.

The down side of the system is that there is no intercommunication on the system so transfer is not possible between stations, though some one is in the same area could verbally ask someone to take the call on their unit.

When an incoming call presents it’s self to the system the lamp for that line will flash on all units and a central audible alarm will sound.  Any attendant can answer the call by moving the switch to the down position, the call may be put on hold by putting the key in the central position.

In practice people would often leave their own phone switched to a particular line and dedicate themselves to that line, if this was generally the case then one wonders if the key and lamp unit was the right choice of system.  In my experience, in a sales environment it worked well, but with a group of people sharing an office then the system had little purpose as people would adopt a line.  The only advantage here was that ten lines could be shared between twenty people saving on PABX lines in a low use area or an area that made more calls than they would normally receive.

Shaun