Electrical symbols are graphic marks used to represent components, connections, and functions in schematics and control diagrams. The same electrical function can look different depending on the drawing convention: a contactor coil may appear as a circle in a common ANSI/IEEE-style drawing and as a rectangle in an IEC-style drawing.
Αυτό το electrical symbols chart compares 29 commonly encountered industrial-control symbols in two columns: ANSI/IEEE style και IEC 60617 style. It covers contacts, timed contacts, operator devices, process switches, coils, actuators, signalling devices, terminals, circuit breakers, and fuses.
Use the chart to identify a symbol family, then confirm the project legend, device tag, terminal numbers, and applicable documentation before wiring or servicing equipment.
What This Electrical Symbols Chart Includes
| Κατηγορία | Symbols covered | Count |
|---|---|---|
| Basic contacts | Contactor N.O./N.C.; control relay N.O./N.C. | 4 |
| Timed contacts | N.O./N.C. on-delay and off-delay contacts | 4 |
| Operator devices | Selector switch; N.O./N.C. pushbuttons; mushroom-head pushbutton | 4 |
| Sensor and process switches | Liquid level, flow, pressure, temperature, limit, and proximity switches | 6 |
| Coils and actuators | Control relay, contactor, motor starter, timer, solenoid, and counter | 6 |
| Signal, connection, and protection | Indicating light, plug/socket, terminals, circuit breaker, and fuse | 5 |
| Σύνολο | 29 |
The chart is deliberately focused on industrial control and low-voltage panel drawings. Electronic-component symbols such as transistors, operational amplifiers, and logic gates belong to a different search intent and are not included here.
Read Four Things Together: Symbol, Tag, Terminal, and State
A symbol rarely gives enough information by itself. Accurate drawing interpretation depends on four separate layers.
| Drawing element | Τι σας λέει | Παράδειγμα |
|---|---|---|
| Graphical symbol | Device function or contact action | Coil, N.O. contact, fuse, circuit breaker |
| Reference designation | Which device instance the symbol belongs to | A project may use CR, KM, KA, QF, or another tag system |
| Terminal marking | Where conductors connect on the physical device | A1/A2, 13/14, 21/22, or manufacturer-specific terminals |
| Normal state and notes | The condition in which the symbol is drawn | De-energized, unactuated, pressure absent, or another defined rest condition |
Reference designations are not simply part of the symbol. Their structure may follow a company convention, a regional practice, or a system based on the IEC 81346 series. If an acronym is unfamiliar, use the project legend and VIOX’s αναφορά με πλήρεις ηλεκτρολογικούς όρους rather than guessing from the letters alone.
Basic Contact Symbols: N.O. and N.C.
Normally open (N.O.) and normally closed (N.C.) contacts are normally shown in their defined rest condition. For an ordinary relay or contactor, that usually means the coil is de-energized and the actuator is not operated.
The graphical shape identifies the contact state, but it does not always identify the complete physical device. A contactor auxiliary contact and a control-relay contact may use the same basic contact geometry. The reference tag connects that contact to the correct coil or device elsewhere in the drawing.
For changeover contacts with more than one pole, see the separate SPDT vs DPDT relay symbol guide.
Timed Contact Symbols: ON-Delay vs OFF-Delay
Timed contacts add a time-dependent action to the normal contact state:
- ON-delay: the timed action occurs after the timing input or coil is energized.
- OFF-delay: the timed action occurs after the initiating signal is removed or the timing condition changes, depending on the device design.
- N.O. or N.C.: describes the contact’s normal state, not the direction of the delay.
Always interpret the contact state and timing mark together. A symbol chart cannot tell you the actual delay range, reset behavior, trigger method, or supply arrangement. Those details come from the device diagram and datasheet. VIOX’s time relay guide explains how the symbol relates to on-delay, off-delay, and other timer functions.
Selector Switch and Pushbutton Symbols
Operator-device symbols combine a contact state with a manual actuator. The chart below compares selector switches, normally open and normally closed pushbuttons, and a general mushroom-head pushbutton.
A mushroom-shaped actuator does not automatically prove that a device is an emergency stop. Emergency-stop functions require the correct device, contact action, safety architecture, marking, and applicable machine requirements. Read the symbol together with the safety notes and equipment documentation instead of identifying the function from actuator shape alone.
Sensor and Process Switch Symbols
Process and position switches use a contact symbol plus a qualifier or actuator mark that indicates what operates the contact. The six examples below cover liquid level, flow, pressure, temperature, limit, and proximity switching.
When reading these symbols, ask two questions:
- What physical variable or movement operates the switch?
- What is the contact state under the drawing’s defined normal condition?
The drawing should also identify the setpoint, device location, process condition, or cross-reference when that information is necessary. The symbol alone does not define calibration range, sensing technology, output type, or environmental rating.
Coil and Actuator Symbols
Coils convert an electrical input into a switching or mechanical action. In common North American control drawings, a relay or contactor coil is often represented by a labelled circle. IEC-style drawings commonly use a rectangle, with a qualifier when the device has a specific action such as timing or solenoid operation.
The coil and its contacts may appear on different pages or in different ladder-diagram rungs. Match them using the reference designation and cross-reference information. Do not assume two similarly shaped coils belong to the same device.
Signal, Connection, and Protection Symbols
The final group covers devices that indicate status, connect conductors, or interrupt abnormal current.
Important boundaries include:
- Ένα indicating light symbol shows a signalling function; its voltage, color, and lamp technology require separate documentation.
- A plug and socket symbol indicates a separable connection, not the physical connector series or pinout.
- A terminal symbol identifies a connection point; terminal numbering and whether it is fused must be confirmed from the drawing and bill of materials.
- A διακόπτης κυκλώματος symbol identifies an interrupting and protection function but does not state the breaker’s rating, trip curve, breaking capacity, or certification.
- A fuse symbol does not by itself identify speed class or application category. For those distinctions, use the detailed fuse electrical symbols guide.
ANSI/IEEE Style vs IEC 60617 Style
The two columns should be treated as drawing languages, not competing levels of quality.
| Point | ANSI/IEEE-style drawings | IEC 60617-style drawings |
|---|---|---|
| Τυπικό πλαίσιο | North American industrial-control documentation and legacy drawing libraries | International electrotechnical diagrams and export-oriented machinery documentation |
| Common visual difference | Coils are often circular and may contain a device abbreviation | Coils are commonly rectangular, with separate qualifiers where needed |
| Ταυτοποίηση συσκευής | Often uses familiar North American abbreviations or project-specific tags | May use IEC-oriented tags or an IEC 81346 reference designation system |
| Final authority | Project legend, applicable documentation, and adopted company/industry practice | Project legend and the IEC 60617 database or adopted project standard |
Το Βάση δεδομένων IEC 60617 is the IEC’s official source for graphical symbols used in electrotechnical diagrams. It contains far more symbols and application metadata than can fit in a practical blog chart.
IEEE/ANSI 315-1975 is still widely referenced in legacy libraries and educational material, but IEEE currently lists it as Inactive-Reserved. For that reason, this article uses the bounded term ANSI/IEEE style rather than claiming that every left-column graphic is a current universal ANSI requirement. Always verify what the contract, customer, authority, or company drawing standard actually requires.
How to Read an Industrial Electrical Drawing
Use this sequence instead of interpreting isolated symbols one at a time.
1. Read the Title Block and Legend
Confirm the drawing type, revision, applicable convention, voltage system, and abbreviation list. If the drawing includes a project-specific legend, it takes priority over assumptions based on a generic chart.
2. Identify the Drawing Type
- A schematic emphasizes electrical function and control logic.
- A διάγραμμα καλωδίωσης emphasizes physical connection points and conductor routing.
- A single-line diagram reduces a multi-conductor power system to a functional overview.
- A panel layout shows physical placement and does not replace the schematic.
3. Establish the Normal Condition
Determine whether the drawing defines devices as de-energized, unpressurized, at rest, or in another normal condition. This is essential when interpreting N.O./N.C. contacts, pressure switches, limit switches, and timed contacts.
4. Trace Power and Control Paths Separately
Follow the main power path through isolation, protection, switching, and the load. Then trace the control path through pushbuttons, interlocks, relay contacts, coils, sensors, and indicators.
5. Match Coils with Contacts
Use tags and cross-references to find every contact operated by a relay, contactor, starter, or timer coil. Physical proximity on the page does not prove that symbols belong to the same device.
6. Verify Terminals Before Wiring
The schematic explains function; the manufacturer’s terminal diagram confirms the actual connection points. Check the device marking, datasheet, wire numbers, terminal plan, and bill of materials before making changes.
For commissioning-stage checks, use the VIOX guide to λάθη ηλεκτρικού πίνακα πριν από την ενεργοποίηση.
Common Electrical Symbol Reading Mistakes
- Treating a chart as a wiring instruction: a symbol comparison does not provide terminal assignments or product ratings.
- Assuming tags are universal: KM, KA, CR, QF, and similar designations depend on the selected reference system and project practice.
- Reading contacts in the operating state: most contact symbols are drawn in a defined normal condition.
- Calling every mushroom-head device an emergency stop: the actuator shape alone does not establish the safety function.
- Confusing a schematic with a panel layout: functional relationships do not show exact mounting position or cable route.
- Ignoring the legend when styles are mixed: imported equipment and modified drawings may contain more than one convention.
ΣΥΧΝΈΣ ΕΡΩΤΉΣΕΙΣ
What Is an Electrical Symbols Chart?
An electrical symbols chart groups graphical marks used to represent devices and functions in schematics. A useful chart also identifies the drawing convention and explains how symbols relate to tags, terminals, and normal states.
Are ANSI and IEC Electrical Symbols the Same?
Not always. Some functions look similar, while others—especially coils, contacts, timed devices, and operator mechanisms—may be drawn differently. The project legend and applicable documentation remain the final authority.
What Is IEC 60617?
IEC 60617 is the IEC database of graphical symbols for electrotechnical diagrams. It covers conductors, components, switchgear, controlgear, protective devices, instruments, signalling devices, and other categories.
What Is the Difference Between IEC 60617 and IEC 81346?
IEC 60617 addresses graphical symbols used in diagrams. The IEC 81346 series addresses system structuring, object classification, and reference designations. A drawing may therefore use an IEC 60617-style symbol and a separate IEC 81346-based device identifier.
Why Can a Contactor Contact and a Relay Contact Look the Same?
The contact symbol describes switching state and action. The associated coil, reference designation, circuit context, and documentation identify whether the contact belongs to a contactor, control relay, timer, or another device.
How Can I Tell Whether a Contact Is Normally Open or Normally Closed?
First establish the drawing’s normal condition. An N.O. contact is open in that condition; an N.C. contact is closed. Do not infer normal state from the equipment’s running condition.
Can I Wire a Component Using Only Its Schematic Symbol?
No. Use the schematic to understand function, then verify terminal markings, voltage, contact arrangement, ratings, and connection instructions from the product documentation.
Is IEEE/ANSI 315 Still an Active Standard?
IEEE lists IEEE/ANSI 315-1975 as Inactive-Reserved. Its graphical conventions remain common in legacy and North American documentation, but current project requirements should be verified rather than assumed.
Πηγές και Τεχνικές Αναφορές
- IEC 60617: Γραφικά σύμβολα για διαγράμματα
- IEEE/ANSI 315-1975 κατάσταση και πεδίο εφαρμογής
- IEC 81346-1:2022—basic rules for reference designations
- IEC 81346-2:2019—classification of objects and class codes
- NFPA 79: Electrical Standard for Industrial Machinery
- c3controls ANSI and IEC Electrical Symbols technical reference
This chart is a practical identification resource, not a substitute for licensed standards, project specifications, or manufacturer wiring instructions.
