Switching and Protection Products Guides 55 technical guides for choosing Switching and Protection Products products: selection criteria, standards, common mistakes and frequently asked questions.
What is the difference between AC-1 and AC-3 utilization categories in contactors? — Compare AC-1 (resistive/non-inductive loads), AC-3 (squirrel-cage induction motors) and AC-4 (plugging/inching) contactor utilization categories under IEC 60947-4-1. What is the difference between Type AC, Type A and Type F/B residual current circuit breakers (30 mA vs 300 mA)? — Compare Type AC, Type A, Type F and Type B residual current circuit breakers (RCCB) by detected fault waveform (sinusoidal AC, pulsating DC, smooth DC) and 30 mA vs 300 mA thresholds. What is the difference between B, C and D curve miniature circuit breakers (MCB)? — Compare B, C and D tripping curve miniature circuit breakers (MCB) across instantaneous magnetic trip multipliers (3–5 In, 5–10 In, 10–20 In), inrush tolerance and applications. What Is a Phase Sequence Relay? Types and Selection Criteria — A phase sequence relay is a monitoring relay that watches the order of the phases in a three-phase supply and opens its contact when the order is reversed, preventing reverse motor rotation. What Is a Blade Fuse Base? NH Sizes and Selection Criteria — A blade fuse base is a fuse carrier that grips an NH blade fuse link with its spring contacts, secures it to the panel and connects it to the line. What Is an Arc Fault Detection Device? Types and Selection Criteria — An arc fault detection device recognises an electric arc from the current waveform or its light and trips the circuit; it comes as the building AFDD or the switchgear arc protection relay. What Is a Modular Switch? DIN Rail Switch-Disconnector Selection Criteria — A modular switch is a DIN rail switch-disconnector that mounts beside circuit breakers, switches a circuit manually under load and isolates it when open. What Is a Gas-Shielded Welding Machine Switch? Types and Selection Criteria — A gas-shielded welding machine switch is a cam switch that sets the welding voltage on step-controlled MIG/MAG machines by switching between the transformer's winding taps. How to Choose a Switch Enclosure: Current, Function and Size — A switch enclosure is a plastic housing that encloses a cam switch's body and terminals so the switch can be surface-mounted outside a panel. What Is a Secondary Overcurrent Protection Relay? Types and Selection — A secondary overcurrent protection relay measures phase and earth current from the CT secondary and sends a trip command to the circuit breaker when the setting is exceeded. What Is a Toroidal Current Transformer? Types and Selection Criteria — A toroidal current transformer is a ring-shaped sensor that detects earth leakage current in the phase and neutral conductors passing through it and feeds it to a residual current relay. What Is a Vertical Load Break Switch? Types and Selection Criteria — A vertical load break switch is a fuse switch disconnector that holds NH fuses in stacked carriers, mounts on the panel busbars and can be opened and closed under load. What Is a Cylindrical Cartridge Fuse? Sizes and Selection Criteria — A cylindrical cartridge fuse is a fuse link fitted in a fuse holder whose fusible element, inside a cylindrical body with metal end caps, opens the circuit on overcurrent and short circuit. What Is a Dahlander Switch? Two-Speed Motor Switch Types and Selection — A Dahlander switch is a cam switch that changes the winding connection of a single-winding three-phase motor to switch by hand between low and high speed in a 2:1 ratio. What Is a Current Protection Relay? Types and Selection Criteria — A current protection relay is an electronic relay that measures load current and, after a delay, switches its contact to open the contactor when current leaves the set upper or lower limit. What Is an Auxiliary Contactor? Contact Arrangements and Selection — An auxiliary contactor is an electromagnetic switch that carries only control contacts instead of main contacts, used in control circuits to multiply signals and build interlocks. What Is a Motor Starter? Types and Selection Criteria — A motor starter is a device that combines the switching element that connects a motor to the supply and the element that protects the motor against overload in one unit. What Is a Shunt Trip Coil? MX, MN, XF and Selection Criteria — A shunt trip coil is a breaker-specific auxiliary coil that opens a circuit breaker remotely on a signal from an emergency stop, fire alarm or protection relay. What Is a Mains Step Switch? Operation and Selection Criteria — A mains step switch is a single-phase step cam switch that Metop offers separately from its cumulative and selector types; its contact arrangement is in the manufacturer's diagram. What Is an RCBO? Types and Selection Criteria — An RCBO is a DIN-rail device that protects a circuit against overload, short circuit and current leaking to earth in a single unit. What Is a Step Switch? Types and Selection Criteria — A step switch is a rotary cam switch that brings heater, fan or transformer stages in one step at a time through positions such as 0-1-2-3. What Is a Load Break Switch? Types and Selection Criteria — A load break switch is a low-voltage switching device that can make and break a circuit under load current and safely isolates the line from the supply when open. What Is a Cam Switch Enclosure? Types and Selection Criteria — A cam switch enclosure covers the body and terminals of a cam switch so that it can be surface-mounted on a wall or machine outside a panel. What Is a Selector Step Switch? Uses and Selection Criteria — A selector step switch is a step-type cam switch that feeds only one output in each position and drops the previous output when the step changes.