These small cabins were provided where a signalman would be stationed regularly to operate a level crossing, points and signals but accomodating only a small number of levers.
The term 'ground frame' described a box which was not also a block post for the regulation of trains, such as at a wayside station on a single line railway to control a level crossing and goods siding or in a busy goods yard to control the movement of shunting engines between the arrival and departure of goods trains.