Circuit Symbols
Drawing style

Relay symbol

A relay symbol pairs a coil with the contacts it moves. In the relay drawn here the contacts are at rest, with the coil de-energised: COM on NC. Energise the coil and COM moves to NO; the printed symbol and its labels do not change.⁠Source 1Source 2Source 3Source 4

Reference Designator K⁠Source 5

On this sheet

Symbol and what it is doing

US style

IEC style

Fig. 1 — Relay (coil and SPDT contact), coil de-energised: COM–⁠NC conducts Relay (coil and SPDT contact), coil energised: COM–⁠NO conducts
COMNCNOA1A2
Fig. 1a — Relay (coil and SPDT contact), coil de-energised: COM–⁠NC conducts
COMNCNOA1A2
Fig. 1b — Relay (coil and SPDT contact), coil energised: COM–⁠NO conducts
COMNCNOA1A2
Fig. 1a — Relay (coil and SPDT contact), coil de-energised: COM–⁠NC conducts
COMNCNOA1A2
Fig. 1b — Relay (coil and SPDT contact), coil energised: COM–⁠NO conducts

Energise the coil. The contact drawn in ink stays at rest; the highlight shows which pair is joined now.

Coil

COM–⁠NC conducts. Under the single-stable relay model, the coil is de-energised and settled: COM–NC is closed and COM–NO is open. This is the drawn resting state.

COM–⁠NO conducts. Under the single-stable relay model, the coil is energised and settled: COM–NO is closed and COM–NC is open. The printed contact stays at rest; only the highlight shows the present position.

In the single-stable changeover relay shown here, energising the coil transfers COM from NC to NO after the operating delay. The printed symbol and its NO/NC labels remain unchanged.

Terminals

COM
COM is the common contact, the one the moving arm belongs to.⁠Source 1
NC
NC is the normally-closed contact: it is connected to COM in the resting, de-energised state of the single-stable relay shown here.⁠Source 1Source 3Source 6
NO
NO is the normally-open contact: it is disconnected from COM at rest and connected after the coil has energised the single-stable relay shown here.⁠Source 1
A1A2
The two coil terminals are the control side of the relay; the current that flows through them moves the contacts.⁠Source 1

Parts of the drawing

  • Relay symbol in US style, with numbered leaders to the coil, the mechanical link and the resting position
1 Resting position
For the non-latching relay shown here, normal means the coil is de-energised. NO contacts are drawn open and NC contacts closed; these labels describe their resting positions.⁠Source 1Source 3Source 4
2 Coil
A relay symbol combines a coil with the contacts it moves, joined by a dashed mechanical link. US drawings show the coil as loops and IEC drawings as a rectangle; a plain switch has no coil.⁠Source 3Source 4
3 Mechanical link
The dashed line between coil and contact is the mechanical link; it carries no current.⁠Source 1
  • Relay symbol in IEC style, with numbered leaders to the coil, the mechanical link and the resting position
1 Resting position
For the non-latching relay shown here, normal means the coil is de-energised. NO contacts are drawn open and NC contacts closed; these labels describe their resting positions.⁠Source 1Source 3Source 4
2 Coil
A relay symbol combines a coil with the contacts it moves, joined by a dashed mechanical link. US drawings show the coil as loops and IEC drawings as a rectangle; a plain switch has no coil.⁠Source 3Source 4
3 Mechanical link
The dashed line between coil and contact is the mechanical link; it carries no current.⁠Source 1
Fig. 2 — Relay symbol, US style, its marks numberedRelay symbol, IEC style, its marks numbered
  • Relay (coil and SPDT contact) symbol, US style, turned 0°, with its terminal names attached

    0°

  • Relay (coil and SPDT contact) symbol, US style, turned 90°, with its terminal names attached

    90°

  • Relay (coil and SPDT contact) symbol, US style, turned 180°, with its terminal names attached

    180°

  • Relay (coil and SPDT contact) symbol, US style, turned 270°, with its terminal names attached

    270°

  • Relay (coil and SPDT contact) symbol, US style, mirrored, with its terminal names attached

    Mirrored

Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing.⁠Source 7

  • Relay (coil and SPDT contact) symbol, IEC style, turned 0°, with its terminal names attached

    0°

  • Relay (coil and SPDT contact) symbol, IEC style, turned 90°, with its terminal names attached

    90°

  • Relay (coil and SPDT contact) symbol, IEC style, turned 180°, with its terminal names attached

    180°

  • Relay (coil and SPDT contact) symbol, IEC style, turned 270°, with its terminal names attached

    270°

  • Relay (coil and SPDT contact) symbol, IEC style, mirrored, with its terminal names attached

    Mirrored

Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing.⁠Source 7

Fig. 3 — Relay (coil and SPDT contact) symbol, US style at 0°, 90°, 180° and 270°, and mirroredRelay (coil and SPDT contact) symbol, IEC style at 0°, 90°, 180° and 270°, and mirrored

Often confused with

    • Relay (coil and SPDT contact) symbol in US style; ringed: dashed mechanical link

      Relay (coil and SPDT contact)

      Dashed mechanical link

    • Inductor symbol in US style

      Inductor

    • Switch (SPDT) symbol in US style; ringed: no coil

      Switch (SPDT)

      No coil

    • Relay (coil and SPDT contact) symbol in IEC style; ringed: dashed mechanical link

      Relay (coil and SPDT contact)

      Dashed mechanical link

    • Inductor symbol in IEC style

      Inductor

    • Switch (SPDT) symbol in IEC style; ringed: no coil

      Switch (SPDT)

      No coil

    Fig. 4 — Relay (coil and SPDT contact), inductor and switch (SPDT), the mark that tells them apart ringedRelay (coil and SPDT contact), inductor and switch (SPDT), the mark that tells them apart ringed

    The sentence that tells these apart is in Fig. 2, the parts of the drawing.

Poles and throws

Single throwDouble throw
Single pole
SPST switch symbol, US style, single pole, single throw: 2 contact terminals

SPST

2 contact terminals
SPDT switch symbol, US style, single pole, double throw: 3 contact terminals

SPDT

3 contact terminals
Double pole
DPST switch symbol, US style, double pole, single throw: 4 contact terminals

DPST

4 contact terminals
DPDT switch symbol, US style, double pole, double throw: 6 contact terminals

DPDT

6 contact terminals

Each pole has a common terminal plus one terminal for each throw. So an SPST switch has 2 contact terminals, SPDT 3, DPST 4 and DPDT 6.⁠Source 1Source 8

Single throwDouble throw
Single pole
SPST switch symbol, IEC style, single pole, single throw: 2 contact terminals

SPST

2 contact terminals
SPDT switch symbol, IEC style, single pole, double throw: 3 contact terminals

SPDT

3 contact terminals
Double pole
DPST switch symbol, IEC style, double pole, single throw: 4 contact terminals

DPST

4 contact terminals
DPDT switch symbol, IEC style, double pole, double throw: 6 contact terminals

DPDT

6 contact terminals

Each pole has a common terminal plus one terminal for each throw. So an SPST switch has 2 contact terminals, SPDT 3, DPST 4 and DPDT 6.⁠Source 1Source 8

Fig. 5 — SPST, SPDT, DPST and DPDT switch symbols, US style, set out by poles and throwsSPST, SPDT, DPST and DPDT switch symbols, IEC style, set out by poles and throws ⁠Source 4Source 8

Notes

The contact drawn here is Form C, a changeover

Form A is another name for a normally-open contact and Form B for a normally-closed one. A single-pole, double-throw contact that has both, sharing a common terminal, is called Form C or a changeover contact.⁠Source 1Source 8 A DPDT relay has two Form C contact sets moved together by one coil. The two poles are electrically isolated from each other, so each can switch a separate circuit.⁠Source 1Source 3 The switch symbol page draws the same forms as hand-worked switches, with the common terminal on the moving arm there too.

A latching relay is drawn in its reset state

A latching relay has no spring-return resting position: it stays in its last position until its coil is signalled again. Its contacts are drawn in the reset state, as a single-stable relay's contacts are drawn at rest.⁠Source 9 The cases on this sheet model the single-stable relay only.

The relay’s own diagram says which number is which

Terminal numbers are printed names, not part of the symbol: relays from different makers can number the same common, normally-open and normally-closed contacts differently. A relay's own diagram says which number is which.⁠Source 1Source 10 The IEC-style 11, 12 and 14 and the automotive 30, 87 and 87a are common schemes, and a given relay may follow either one or neither.

NC can also mean not connected

NC has two unrelated meanings. At a switch or relay contact it means normally closed; on an integrated-circuit pin diagram, nc marks a pin that is not connected.⁠Source 1Source 11 Beside a relay contact, read NC as normally closed, the partner of normally open.

Check your reading

More questions on the practice page

Pick an answer to see the reason.

  1. Question 1

    The coil is de-energised. Which contacts are joined?

    COMNCNOA1A2

    Upper part: a lead labelled COM comes in from the left and ends in a hinged arm. On the right are two contacts, the upper labelled NC and the lower NO, and the arm is drawn against the upper one. Lower part: a row of loops between leads labelled A1 and A2. A dashed line runs from the loops up to the arm.

    COMNCNOA1A2

    Upper part: a lead labelled COM comes in from the left and ends in a hinged arm. On the right are two contacts, the upper labelled NC and the lower NO, and the arm is drawn against the upper one. Lower part: a rectangle between leads labelled A1 and A2. A dashed line runs from the rectangle up to the arm.

    Not this one Right Answer

    The answer is “COM and NC”. For the non-latching relay shown here, normal means the coil is de-energised. NO contacts are drawn open and NC contacts closed; these labels describe their resting positions.COM is the common contact, the one the moving arm belongs to.NC is the normally-closed contact: it is connected to COM in the resting, de-energised state of the single-stable relay shown here. Under the single-stable relay model, the coil is de-energised and settled: COM–NC is closed and COM–NO is open. This is the drawn resting state.

  2. Question 2

    The coil is now energised. What happens to the printed NO and NC labels?

    COMNCNOA1A2

    The relay as printed: COM on the left, NC upper right, NO lower right, the arm drawn against NC, and a row of loops between A1 and A2 with a dashed line up to the arm. A highlight marks the coil as energised and shows COM joined to NO; the printed arm and labels are unchanged.

    COMNCNOA1A2

    The relay as printed: COM on the left, NC upper right, NO lower right, the arm drawn against NC, and a rectangle between A1 and A2 with a dashed line up to the arm. A highlight marks the coil as energised and shows COM joined to NO; the printed arm and labels are unchanged.

    Not this one Right Answer

    The answer is “Nothing: they name the resting positions”. For the non-latching relay shown here, normal means the coil is de-energised. NO contacts are drawn open and NC contacts closed; these labels describe their resting positions.In every case the printed relay contact stays drawn in its resting, de-energised position, and the NO and NC labels stay where they are. Only the highlight shows the present position. In the single-stable changeover relay shown here, energising the coil transfers COM from NC to NO after the operating delay. The printed symbol and its NO/NC labels remain unchanged.

  3. Question 3

    The contact labels are hidden. What is the terminal on the moving arm called?

    ???A1A2

    Upper part: a lead labelled ? comes in from the left and ends in a hinged arm. On the right are two contacts, each labelled ?, and the arm is drawn against the upper one. Lower part: a rectangle between leads labelled A1 and A2. A dashed line runs from the rectangle up to the arm.

    Not this one Right Answer

    The answer is “COM”. NO is the normally-open contact: it is disconnected from COM at rest and connected after the coil has energised the single-stable relay shown here.NC is the normally-closed contact: it is connected to COM in the resting, de-energised state of the single-stable relay shown here.The two coil terminals are the control side of the relay; the current that flows through them moves the contacts. COM is the common contact, the one the moving arm belongs to.

  4. Question 4

    What does the dashed line between the coil and the contact carry?

    COMNCNOA1A2

    Upper part: a lead labelled COM comes in from the left and ends in a hinged arm, drawn against the upper of two contacts labelled NC and NO. Lower part: a row of loops between leads labelled A1 and A2. A dashed line runs from the top of the loops up to the arm.

    Not this one Right Answer

    The answer is “No current: it is a mechanical link”. A dashed line joining parts of a symbol shows a mechanical link: the parts move together, but the line is not a wire and carries no current.The electromechanical relay shown here uses a coil to move contacts. Its coil circuit is electrically separate from the switched contact circuit. The dashed line between coil and contact is the mechanical link; it carries no current.

  5. Question 5

    Automotive relays often number their terminals 85, 86, 30, 87 and 87a. Which number names the common contact?

    Not this one Right Answer

    The answer is “30”. Automotive relays often carry numbers from the German DIN 72552 terminal scheme instead of COM, NO and NC: 85 and 86 are the coil terminals, 30 is the common contact, 87 the normally-open contact and 87a the normally-closed contact.

Answer key

  1. 1

    COM and NC

    COMNCNOA1A2
    COMNCNOA1A2
  2. 2

    Nothing: they name the resting positions

  3. 3

    COM

  4. 4

    No current: it is a mechanical link

  5. 5

    30

Questions

What do NO and NC mean on a relay?
Normally open and normally closed, where normally means with the coil de-energised. At rest NC is joined to COM and NO is not; once the coil is energised, COM joins NO.⁠Source 1Source 3Source 6
What do 11, 12, 14, A1 and A2 mean on a relay?
They are IEC-style terminal names. A1 and A2 are the coil. Contact terminals have two digits: the first counts the contact set and the second gives its function, so 11 is common, 12 normally closed and 14 normally open.⁠Source 10Source 12Source 13Source 14
What do 85, 86, 30, 87 and 87a mean on a relay?
They are automotive terminal names from the DIN 72552 scheme: 85 and 86 are the coil, 30 is the common contact, 87 normally open and 87a normally closed. They are names only; the relay's own diagram decides.⁠Source 6Source 15Source 16

Print and files

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Sources

17 sources, numbered as cited
  1. ModEL — Electromechanical Relays, §§3.2–3.3 and §5.1 (normal and present contact status)

    Tony R. Kuphaldt, retrieved 2026-09-22.

  2. Relay technology — structure, operation and contact forms

    Omron, retrieved 2026-09-22.

  3. ModEL — Components and Symbols, §3.11 (relay symbol, p. 21)

    Tony R. Kuphaldt, retrieved 2026-09-23. The schematic diagram symbol for a relay (shown on the left) is a combination of symbols – a solenoid shown mechanically linked to a switch.

  4. ModEL — Components and Symbols, §3.8 (switch symbols, poles, throws and dashed links, pp. 15–16)

    Tony R. Kuphaldt, retrieved 2026-09-23. Note the use of dashed lines to represent a mechanical connection between moving pieces of a component without implying an electrical connection between the same.

  5. Design to Manufacturing Standards — Reference Designators (slide 33)

    Dieter Bergman, IPC, retrieved 2026-09-22. BT battery … CB circuit breaker … DS display, lamp, light emitting diode … RT thermistor

  6. AT121 course notes — Relays: ISO relay contact numbers

    Community College of Philadelphia (D. Reed), reproducing with permission an MG Car Club article by Rick Astley, retrieved 2026-09-23. 85 Coil Low 86 Coil High 87 NO contact 87A NC contact 30* Common

  7. Electrical Schematics, §§1.3.1–1.3.5 — nodes, crossings, references and congruent drawings

    Tufts University, retrieved 2026-09-22.

  8. ModEL — Electrical Switches, §§3.1–3.3 (pp. 16–19)

    Tony R. Kuphaldt, retrieved 2026-09-22.

  9. ModEL — Electromechanical Relays, §3.7 (latching relays, p. 41)

    Tony R. Kuphaldt, retrieved 2026-09-23. Latching relay contacts are always drawn in their reset states, much like regular relay contacts are always drawn in their resting states.

  10. Info Byte: What’s the Reason Behind Relay Terminal Numbering? (23 February 2022)

    David Peterson, Control.com, retrieved 2026-09-23. for the first contact set, the common would read 11 … the N.C would read 12 … and the N.O. would read 14

  11. Lessons In Electric Circuits, Vol. IV — §12, shift-register pin diagram (nc pins, p. 356)

    Tony R. Kuphaldt, retrieved 2026-09-23. A number of pins are not connected (nc).

  12. ModEL — AC Induction Motor Starters, §2.1 (contactor coil terminals A1 and A2, pp. 7–9)

    Tony R. Kuphaldt, retrieved 2026-09-23. two small screw terminals (commonly denoted A1 and A2) providing connection points to the electromagnet coil actuating the contactor

  13. Motor Branch Circuits Basics, IEC & NEMA Devices — numbers on IEC relay terminals (slides 17 and 24)

    Tom Wylie, IND223 course module, hosted by ATE Central (NSF Advanced Technological Education), retrieved 2026-09-23. The first digit of each number is the contact number … 3 & 4, the contact is normally open … 1 & 2, the contact is normally closed … A1 & A2 is always the coil

  14. IEC 60947-5-1:2024 — control circuit devices; public preview contents, Annex M (preview p. 6)

    International Electrotechnical Commission, retrieved 2026-09-23. Annex M (normative) Terminal marking, distinctive number and distinctive letter for control circuit devices … M.2.2 Function digit … M.2.3 Sequence digit

  15. Electromechanical: Switches and Relays (30 May 2024)

    Steven McDermott, CSE Senior Design Knowledge Base, University of Texas at Arlington, retrieved 2026-09-23. Pins 85 and 86 are connected to the coil, pin 30 is the common, and pin 87 is the Normally Open (closed when energized) contact.

  16. DIN 72552-2:2014-07 — Terminal markings for vehicles, Part 2: Codes (status page)

    DIN Media, retrieved 2026-09-23. This part of the standard series DIN 72552 specifies codes of terminal markings.

  17. ModEL — Components and Symbols, §3.20 (wire crossings and dashed links, p. 36)

    Tony R. Kuphaldt, retrieved 2026-09-23. use the new convention (dot) to show connections between wires, and the old convention (“loop”) to show wires crossing over each other without connection