This industrial electrical symbols reference chart gives you a quick way to review common schematic and control panel symbols used in automation, PLC systems, relay logic, motor circuits, sensors, pushbuttons, overloads, transformers, and safety devices.
If you work with electrical prints, ladder diagrams, panel layouts, machine wiring, or troubleshooting documents, understanding symbols helps you trace circuits faster and avoid wiring mistakes. This page is meant to be a practical reference for industrial maintenance, controls engineers, electricians, technicians, PLC programmers, and machine builders.
If you're troubleshooting a PLC input, relay circuit, control panel problem, sensor issue, or machine wiring question, I can help point you in the right direction or connect you with an integrator.
Find Help / Connect With an IntegratorThese symbols are used to show system power, common references, and grounding points. In industrial controls, they often appear around incoming power, control transformers, 24VDC supplies, and field device circuits.
Shows a connection to earth ground or system reference ground, depending on drawing style and application.
Common for 24VDC control power, sensors, PLC modules, and instrumentation circuits.
Used for machine power feeds, transformers, branch circuits, and some control voltage sources.
Protection and switching components are used to isolate power, protect equipment, and control whether power is allowed to pass through a circuit. These are common around disconnects, branch protection, and control power distribution.
Protects a circuit against overcurrent and is often used on control power, transformers, and branch circuits.
Provides resettable overcurrent protection and may serve as a branch isolation device.
Used for machine isolation, service access, and lockout/tagout points.
Relays and contactors are everywhere in industrial electrical drawings. Their coils change the state of associated contacts, which then switch loads, send status signals, or create control logic sequences.
The coil is the actuating element. When energized, it changes the state of related contacts shown elsewhere in the print.
Open in the normal state and closes when actuated or when the linked coil energizes.
Closed in the normal state and opens when actuated or when the linked coil energizes.
These symbols show power conversion and driven equipment. They are common on motor starter circuits, transformer-fed controls, and machine distribution sections.
Represents a motor load such as a conveyor, fan, pump, or driven machine axis.
Steps voltage up or down and often feeds machine control voltage or auxiliary circuits.
Protects motors against overload conditions and often provides an auxiliary fault contact for logic interruption or alarm status.
These are the devices people interact with and the components machines use to detect position, presence, and status. They are common in operator stations, guard doors, workholding, conveyors, and assembly equipment.
Used for start, stop, reset, cycle start, manual commands, and station control functions.
Used for machine status indication such as power on, cycle active, fault, or safety status.
Represents a non-contact sensor for part detection, cylinder position, machine homing, or interlock confirmation.
PLC-related symbols are especially useful for beginners learning how field devices connect to controller inputs and outputs. These symbols help tie prints back to the actual terminal and I/O hardware in the panel.
Used to organize field wire landings, simplify troubleshooting, and separate panel wiring from machine wiring.
Represents a controller input receiving a signal from a switch, sensor, relay contact, or interlock device.
Represents a controller output driving a relay coil, contactor, solenoid valve, indicator, or other electrical load.
Safety circuits use special devices and logic paths to reduce risk when hazardous motion or stored energy is present. These symbols are common on guarded cells, robot systems, presses, conveyors, and automated machinery.
Used to command a rapid safe stop or energy removal condition when an emergency exists.
Monitors safety devices and helps validate dual-channel safety inputs, reset logic, and output monitoring.
Used on access doors, safety gates, or removable guards to detect whether a protective barrier is closed and monitored.
This symbol legend table gives you a text-based reference for what each common industrial electrical symbol usually means and where you are likely to see it in real machine prints. This also helps make the page more searchable for people looking for relay symbols, motor symbols, PLC wiring symbols, or control panel references.
| Symbol | Typical Meaning | Where You Usually See It |
|---|---|---|
| Ground | Earth ground or common electrical reference point | Main panels, power supplies, shields, machine grounding points |
| DC Supply | Direct current control power, often 24VDC | Sensors, PLC I/O, instrumentation, valve manifolds |
| AC Supply | Alternating current power source | Incoming power, control transformers, auxiliary devices |
| Fuse | Overcurrent protection device | Branch circuits, transformer protection, control power circuits |
| Circuit Breaker | Resettable protective switching device | Incoming feeders, motor branches, control branches |
| Disconnect Switch | Isolation point for power removal | Machine main disconnects, service access points |
| Relay / Contactor Coil | Actuating coil that changes contact state | Motor starters, interposing relays, control logic |
| Normally Open Contact | Contact closes when actuated | Start circuits, permissives, relay logic, PLC interlocks |
| Normally Closed Contact | Contact opens when actuated | Stop circuits, faults, overload trips, safety loops |
| Motor | Electric motor load | Conveyors, pumps, fans, tooling drives, machinery |
| Transformer | Voltage conversion device | Control voltage circuits, isolation power sections |
| Overload Relay | Motor overload protection | Motor starters, reversing starters, protection circuits |
| Pushbutton | Operator command device | Stations, HMIs with hard controls, machine panels |
| Pilot Light | Status indicator lamp | Operator panels, stacklights, fault/status indication |
| Proximity Sensor | Non-contact detection device | Part presence, cylinder position, homing, interlocks |
| Terminal Block | Field wire termination point | Control panels, junction boxes, I/O marshalling |
| PLC Input | Controller signal input point | Switches, sensors, safety monitoring, feedback signals |
| PLC Output | Controller-driven load output point | Relays, solenoids, indicators, contactor coils |
| E-Stop | Emergency stop device | Stations, guard perimeters, hazardous machine zones |
| Safety Relay | Monitored safety logic device | Guard circuits, dual-channel safety, monitored outputs |
| Guard Door Switch | Detects guard or gate closure | Robot cells, machine guards, access doors |
No. Many symbols are similar across standards, but print styles still vary by company, OEM, industry, and drawing package. The function is usually more important than tiny differences in appearance.
They can look very similar in prints. In practice, a contactor is usually used for switching larger loads like motors, while relays are often used for lighter-duty control logic and interposing functions.
Because “normally” means the device’s unactuated or de-energized state, not the machine’s everyday running condition. That trips people up all the time.
No. Use it as a fast reference, but always go back to the actual machine drawing legend and customer standards when making wiring or troubleshooting decisions.
Work through common PLC, HMI, network, and device communication issues.
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Review common conductor sizes and current ranges for practical electrical planning.
Convert raw PLC analog values into useful engineering units.
Understand how fast-changing signals can be missed and how to handle them correctly.
Browse the full collection of calculators, charts, and troubleshooting tools.
The best follow-up to this page is either a Control Panel Components Guide or a PLC I/O Wiring Basics Guide. That would give you better internal linking and make this symbols page more useful to beginners.