Industrial Electrical Symbols
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Industrial Symbols for Transforms Industrial Symbols for Metering
Partial Glossary for Selectors
Resistor: Resistors restrict the flow of current. Used with a capacitor in a timing circuit.
Ground: Connection to the actual ground or other “grounding” structure. Used to provide electrical shock protection and for zero potential references.
Capacitor: Stores electric charge. Can be used to filter or block DC signals while passing AC signals. Used with a resistor in a timing circuit.
Battery: Generates constant voltage and supplies electrical energy.
Fuse: Sacrificial overcurrent protection device. This symbol represents low power/low voltage fuses.
Inductor: Coil of wire that generates a magnetic field when electrical current is passed through it. Passive two-terminal electrical component used to store energy in the resulting magnetic field. Can also be used as a transducer to convert electrical energy into mechanical energy.
Iron Core Inductor: Same as above, but with an iron core beneath the coiled wire.
Circuit Breaker: Automatically operated electrical switch that protects electrical circuits from damage caused by short circuits or overloads.
Voltmeter: Very high resistance device used to measure electrical voltage. Must be connected in parallel.
Ammeter: Zero resistance device used to measure electrical current. Must be connected serially.
Wattmeter: Device used to measure electric power.
Bell: Electric bell, makes a single tone or repeated ringing sound when activated.
Buzzer: Similar to an electric bell, an electric buzzer makes a constant buzz when activated.
SPST (Single-Pole, Single-Throw): A simple switch with one input and one output. Switch will be either closed or completely disconnected. Requires only two terminals. Ideal for on/off switching.
SPDT (Single-Pole, Double-Throw): A switch utilizing three terminals: one common pin, two pins vying for connection to the common (only one can be connected at a time). Ideal for selecting between two power sources or swapping inputs. Can be made into an SPST switch by simply leaving one of the throw pins unconnected.
DPST (Double-Pole, Single-Throw): Essentially a doubled SPST. A switch with two inputs and two outputs; each input corresponds to one of the outputs. DPST switches provide versatility, as they can accept two inputs and drive two different outputs to the same circuit.
DPDT (Double-Pole, Double-Throw): Essentially two SPDT switches, controlling two different circuits, and always switched on together from a single actuator. Require six terminals.
NO (Normally Open): The “normal” state for a switch is its nonactuated position. Depending on its construction, a switch’s normal state can produce an open circuit or a short circuit. When open until actuated, a switch is a normally open (NO) switch; when activated, a NO switch closes the circuit.
NC (Normally Closed): Essentially the “opposite” of an NO switch. A switch that creates a short circuit when not actuated. Normally closed (NC) switches create a short circuit when actuated.