Switchboards, Busbars and Compartments

Switchgear is the assembly of switching and protective devices that distributes power and isolates faults. A switchboard houses those devices around a common busbar system.

Busbars

Copper or aluminium bars carrying the full board current. They are sized for continuous current, for the temperature rise permitted, and critically for the short circuit withstand — the mechanical force between busbars during a fault is enormous, and bracing and support spacing are what resist it. Busbar joints are the weak point: a joint with insufficient bolt torque or with oxidised surfaces develops resistance, heats, oxidises further and eventually fails as an arcing fault. This is why thermographic survey of switchgear is so valuable.

Forms of separation

Switchboards are classified by how far the busbars, the functional units and the terminals are separated from one another by barriers. Higher forms of separation allow work on one circuit while adjacent circuits remain live, and contain the effects of a fault. The form of separation is a design decision that determines what maintenance is possible without a full shutdown — it is worth knowing what your board actually provides before planning work on it.

Withdrawable and fixed

A withdrawable circuit breaker or motor starter can be racked out to a test or isolated position, giving a visible, verifiable isolation with shutters closing over the live busbar contacts. A fixed pattern unit requires the board or section to be isolated upstream. Withdrawable equipment is standard on medium voltage and on motor control centres, precisely because it makes safe isolation practical.

Ingress protection and environment

Switchgear in oilfield environments is attacked by dust, humidity, salt and temperature cycling. Enclosure sealing, anti-condensation heaters, filtered ventilation and clean, dry room conditions are not optional extras — condensation on insulation is a leading cause of switchgear failure, and a switchroom air conditioning failure is an electrical integrity issue.