Properties:

An item used specifically to perform functions such as controlling, protecting, measuring and switching for interior communication systems. May include such items as switch units, switches, variable resistors, relays, meters, fuses, synchro overload indicating devices, terminal boards, and wiring and may be sectionalized. (for the purpose of this definition, a section is defined as a self-contained structure mounted on a common base consisting of a complete framework with all required inclosures.)