Electric distribution delivery systems comprise primary devices that deliver power and secondary devices that protect and allow control of the primary devices. This chapter covers the selection of this primary and secondary equipment, starting with the primary switch. The primary switchgear service duty is designated by current breaking capacity, current making capability, normal current rating, operating cycle and voltage class. Circuit breakers are provided to connect the secondary side of each transformer to the busbar, to supply the outgoing feeders and to divide the busbar into two sections. Most manufacturers now offer nonisolatable switchgear for primary substations. A number of manufacturers use compressed gas as their energy storage instead of mechanical energy stored in a spring, and this is more common in pole-mounted switchgear. Depending on the type of fault passage indicator (FPI) fitted to any particular substation, it may be possible to replace the FPI sensors with the instrument transformers.