Industrial Electrical Symbols

Barish Pump Company Inc. offers this guide to common industrial electrical symbols to help you correctly identify components and spot potential hazards. Bookmark this page as a handy reference for future electrical projects. Safety first!

Partial Glossary

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 reference.

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.