Core concepts, equipment, ratings and configurations.
Switchgear ratings are declared for specified normal service conditions. When the installation is hotter, higher, dirtier, more humid or mechanically demanding, the product may require derating, special design measures or project-specific qualification. Learning objectives Translate environmental data into insulation, thermal, enclosure and maintenance decisions, and avoid applying one generic derating factor to unrelated phenomena. Core…
Circuit breakers are not the only switching devices used in MV assemblies. Load-break switches, switch-fuse combinations and contactors can be technically superior for defined duties when their switching capability, endurance and protection coordination are understood. Learning objectives Choose the device family from the protected load and operating duty, distinguish switching from fault interruption and coordinate…
Disconnectors and earthing switches create controlled electrical states for operation and maintenance. Their symbols can look simple, but the functions—isolating distance, current-carrying duty, induced-current switching and short-circuit making—must be specified precisely. Learning objectives Distinguish disconnection from load interruption, understand earthing-switch duties and design an interlocked sequence that prevents energising an earthed circuit. Core engineering principles…
A switchgear feeder is not complete until the project cable can be safely installed, tested, earthed and maintained. Cable compartments frequently become the critical interface because electrical ratings, connector standards and physical routing must all agree. Learning objectives Translate cable data into compartment space and interface requirements, coordinate CTs and surge arresters, and prevent late…
The protective circuit of an MV switchboard must provide a reliable path for fault current and maintain equipotential bonding of exposed conductive parts. A continuity beep is useful for workmanship, but it does not prove the thermal and mechanical duty of the earthing system. Learning objectives Trace every possible fault-current return path, distinguish protective bonding…
Busbar reliability depends on far more than conductor size. Joints create resistance and heat, supports carry electrodynamic forces, and the enclosure changes both cooling and electromagnetic behaviour. Most field hotspots originate at interfaces rather than along uniform copper. Learning objectives Design and review busbar systems by controlling current path, joint mechanics, thermal expansion, insulation spacing…
Internal Arc Classification (IAC) records the performance of a metal-enclosed switchgear assembly during a specified internal-arc test. A complete claim includes accessibility type, accessible sides, test current and duration. The letters IAC alone do not describe the result. Learning objectives Read an IAC designation correctly, understand the installation conditions that support it and separate product…
Partition class describes the nature of the barrier between opened accessible compartments and hazardous live parts of the main circuit. PM and PI are precise assembly classifications; they should not be used as vague synonyms for metal-clad or insulated switchgear. Learning objectives Distinguish metallic and non-metallic partitions, understand the role of shutters and connect partition…
Loss of Service Continuity (LSC) categories describe how much of the main circuit may remain energised when a defined accessible high-voltage compartment is opened. They are access and continuity classifications, not universal reliability scores. Learning objectives Interpret LSC1, LSC2A and LSC2B correctly, connect the category to the actual accessible compartment and avoid claims that exceed…
Compartment names are useful only when they describe physical boundaries and access conditions. Engineers must know which live parts are contained, how access is controlled and what remains energised when a cover or door is opened. Learning objectives Identify the principal MV switchgear compartments, distinguish access control methods and verify that maintenance assumptions match the…