1. Apparatus for providing an interface between a programmable controller and a plurality of units controlled by the programmable controller comprising: a housing, a plurality of frames rigidly attached to the housing, a plurality of modular elements slidably disposed within the plurality of frames, each modular element comprising: first, second and third vertically disposed power plugs disposed at one end of the modular element, a vertically disposed modular element multibus connector disposed at one end of the modular element, a plurality of output terminals disposed at another end of the modular element, each frame comprising: first, second and third horizontally disposed frame supply buses, the first frame supply bus being aligned with and connected to the first power plug of each modular element within the frame, the second frame supply bus being aligned with and connected to the second power plug of each modular element within the frame, the third frame supply bus being aligned with and connected to the third power plug of each modular element with the frame, a frame multibus connector horizontally disposed adjacent to the first, second and third frame buses and being so positioned that it is aligned with and is connected to each modular element multibus connector disposed in the frame, a frame connector connected to the frame multibus connector, the housing comprising: a vertically disposed housing multibus aligned with and connected to each frame connector thereby providing a connection to each frame multibus connector, first, second and third vertically disposed housing power buses, the first housing power bus being aligned with and connected to each first frame supply bus, the second housing power bus being aligned with and connected to each second frame supply bus, the third housing power bus being aligned with and connected to each third frame supply bus, the housing multibus being connected to the programmable controller, the plurality of output terminals of the modular elements being connected to the plurality of units controlled by the programmable controller.