Circuit Symbols
Drawing style

How to read a schematic

A schematic shows how parts connect, not where they sit. Wire that runs unbroken is one node. A dot or a T joins wires; in the convention used here a plain crossing does not. Letters such as R1 name the parts.⁠Source 1Source 2Source 3Source 4

On this sheet

Trace a node

Choose a node, or tap a wire in the drawing. Every conductor on that node lights up.

Circuit 1 Torch

No node selected.

Node 1: Cell positive to switch. Joins BT1 + and S1 terminal 1.

Node 2: Switch to lamp. Joins S1 terminal 2 and DS1 terminal 1.

Node 3: Lamp back to cell negative. Joins DS1 terminal 2 and BT1 −.

Fig. 1 — Torch: BT1, S1 and DS1

Nodes in Fig. 1

Parts

BT1
Cell
S1
Switch (SPST)
DS1
Lamp

Questions on Fig. 1

  1. Is the switch's right-hand terminal on the same node as the lamp's upper terminal?

    Check the answer

    Yes. One wire runs from S1 terminal 2 to DS1 terminal 1 with no part between them, so the two terminals are one node. ⁠Source 1Source 2

  2. How many nodes does this circuit have?

    Check the answer

    Three: cell + to the switch, the switch to the lamp, and the lamp back to cell −. Each part sits between two of them. ⁠Source 1Source 2

Four reading rules

  1. 1 Designators and values

    Reference designators identify parts with class letters and a number. Common letters used here are R resistor, C capacitor, D diode, Q transistor, L inductor, T transformer, S switch, K relay and F fuse; other naming systems exist.⁠Source 4

    Values printed beside a symbol may put the multiplier letter where the decimal point would be: 4k7 means 4.7 kΩ, 3R9 means 3.9 Ω, 47R means 47 Ω and 2M2 means 2.2 MΩ. IEC 60062 sets out this letter code.⁠Source 5Source 6Source 7

    Capacitor values use the same idea with p and n: 2p2 is 2.2 pF and 2n2 is 2.2 nF. Some makers write R instead on a capacitor, where 2R2 means 2.2 pF rather than 2.2 Ω.⁠Source 7Source 8

    A reading aid only; this site gives no advice on choosing values.

    R14k7C12n2K1
    R14k7C12n2K1
    Fig. 2 — Designators and printed values: R1 marked 4k7, C1 marked 2n2, and relay K1

  2. 2 Junctions and crossings

    In the drawing convention used here, a dot marks a wire connection and a plain four-way crossing without a dot is not connected. Older drawings may use another convention, so check their legend.⁠Source 1Source 3

    Wires that meet in a T are connected whether or not a dot is drawn there. Where four wires cross and connect, the dot is what shows it.⁠Source 1

    A small half-circle hop where one wire passes over another also means the wires are not connected. Some drawings put a hop at every unconnected crossing and a dot at every connection, so neither is left to guess.⁠Source 1Source 3Source 9

    JoinedDotT, dotT, no dotNot joinedNo dotHop
    Fig. 3 — Five ways wires meet or cross

  3. 3 Nodes

    In the ideal-wire schematic model, a node is the set of points connected by uninterrupted wire. Those points share one potential; real wire resistance and other wire effects are omitted.⁠Source 1Source 2

    BT1S1DS1Node 2
    BT1S1DS1Node 2
    Fig. 4 — The torch from Fig. 1 with Node 2 drawn heavy: S1 terminal 2, DS1 terminal 1 and the wire between them

  4. 4 Rails and references

    Within the drawing's stated scope, repeated supply or reference labels identify the same node without a drawn wire between them. Different labels or reference symbols must not be assumed connected.⁠Source 1

    A supply connection is often drawn as a short labelled stub or dot, such as +5 V, VCC or VDD, instead of a wire back to the source. The source's other side is taken to be the ground reference, and every stub with the same label is the same node.⁠Source 1Source 5Source 10

    A label such as GND, Gnd or 0 V at a reference symbol names the node that other potentials are measured from. A drawing may keep separate commons, such as an analog signal common and a digital logic common, so differently named references must not be assumed to be joined.⁠Source 1Source 2Source 5

    +5 V+5 VSame label: one node0 V0 VSame label: one node0 VEarthDifferent references: not assumed joined
    Fig. 5 — Two +5 V supply stubs, two 0 V reference marks, then a 0 V mark beside an earth mark

Five more circuits

Each one practises the rules above. Pick a circuit, trace it, then answer its questions.

Circuit

Circuit 2 Series chain

No node selected.

Node 1: Cell positive to R1 terminal 1. Joins BT1 + and R1 terminal 1.

Node 2: R1 terminal 2 to R2 terminal 1. Joins R1 terminal 2 and R2 terminal 1.

Node 3: R2 terminal 2 to lamp terminal 2. Joins R2 terminal 2 and DS1 terminal 2.

Node 4: Lamp terminal 1 back to cell negative. Joins DS1 terminal 1 and BT1 −.

Fig. 6 — Series chain: BT1, R1, R2 and DS1

Nodes in Fig. 6

Parts

BT1
Cell
R1
First resistor
R2
Second resistor
DS1
Lamp

Questions on Fig. 6

  1. Which node joins R1 to R2?

    Check the answer

    The wire from R1 terminal 2 to R2 terminal 1. Nothing else touches it, so that node joins only those two terminals. ⁠Source 1Source 2

  2. Are the cell negative terminal and the lower terminal of R2 on the same wire node, or is DS1 between them?

    Check the answer

    DS1 is between them. R2 terminal 2 shares a node with DS1 terminal 2, and DS1 terminal 1 shares a node with the cell's − terminal, so the two are on different nodes. ⁠Source 1Source 2

Circuit 3 Parallel branches

No node selected.

Node 1: Upper rail: cell positive and both resistor terminal 1 connections. Joins BT1 +, R1 terminal 1 and R2 terminal 1.

Node 2: Lower rail: cell negative and both resistor terminal 2 connections. Joins BT1 −, R1 terminal 2 and R2 terminal 2.

Fig. 7 — Parallel branches: BT1, R1 and R2, with two junction dots

Nodes in Fig. 7

Parts

BT1
Cell
R1
First branch resistor
R2
Second branch resistor

Questions on Fig. 7

  1. Do both upper resistor terminals share a node?

    Check the answer

    Yes. The upper rail joins R1 terminal 1, R2 terminal 1 and the cell's + terminal; the dot marks where R1's branch meets the rail. ⁠Source 1Source 3

  2. At each junction dot, which three conductor directions meet?

    Check the answer

    At the upper dot: the rail from the cell on the left, the rail on to R2 on the right, and R1 terminal 1 below. The lower dot is the same, with R1 terminal 2 above. ⁠Source 1Source 3

Circuit 4 Crossing paths

No node selected.

Node 1: Left continuation to R1 terminal 1. Joins R1 terminal 1.

Node 2: Horizontal link from R1 terminal 2 to R2 terminal 1. Joins R1 terminal 2 and R2 terminal 1.

Node 3: R2 terminal 2 to the right continuation. Joins R2 terminal 2.

Node 4: Upper continuation to C1 terminal 1. Joins C1 terminal 1.

Node 5: C1 terminal 2 to the lower continuation. Joins C1 terminal 2.

Fig. 8 — Crossing paths: R1, R2 and C1, with one crossing

Nodes in Fig. 8

Parts

R1
Left resistor
R2
Right resistor
C1
Capacitor on the vertical path

Questions on Fig. 8

  1. Does the horizontal resistor link join the upper capacitor lead at the crossing?

    Check the answer

    No. The vertical wire crosses the link with no dot, so R1 terminal 2 and C1 terminal 1 stay on different nodes. ⁠Source 3

  2. Which two resistor terminals share the horizontal link node?

    Check the answer

    R1 terminal 2 and R2 terminal 1. The wire that crosses the link has no dot there, so it adds nothing to that node. ⁠Source 3

Circuit 5 Labelled return

No node selected.

Node 1: Cell positive to R1 terminal 1. Joins BT1 + and R1 terminal 1.

Node 2: Shared signal-reference node: cell negative, R1 terminal 2 and both REF marks. Joins BT1 −, left REF mark, R1 terminal 2 and right REF mark.

Fig. 9 — Labelled return: BT1 and R1, with two reference marks

Nodes in Fig. 9

Parts

BT1
Cell
R1
Resistor
REF
Signal-reference mark labelled REF, under the cell
REF
Signal-reference mark labelled REF, on the right

Questions on Fig. 9

  1. Which two separated drawing fragments belong to REF?

    Check the answer

    The left fragment, the cell's − terminal with the REF mark under it, and the right fragment, the wire from R1 terminal 2 down to the second REF mark. The repeated REF label makes them one node. ⁠Source 1

  2. Do the cell negative terminal and R1 terminal 2 share a node even though no return wire is drawn between the REF marks?

    Check the answer

    Yes. Both marks carry the same REF label, so the drawing treats them as one node without a drawn wire between them. ⁠Source 1

Circuit 6 Relay separation

No node selected.

Node 1: BT1 positive to relay coil A1. Joins BT1 + and K1 A1.

Node 2: Relay coil A2 to BT1 negative. Joins K1 A2 and BT1 −.

Node 3: BT2 positive to R1 terminal 1. Joins BT2 + and R1 terminal 1.

Node 4: R1 terminal 2 to relay NC. Joins R1 terminal 2 and K1 NC.

Node 5: Relay COM to BT2 negative. Joins K1 COM and BT2 −.

Node 6: Relay NO continuation without another component. Joins K1 NO.

Fig. 10 — Relay separation: K1, BT1, BT2 and R1

Nodes in Fig. 10

Parts

K1
Relay with a coil and changeover contact
BT1
Cell in the coil circuit
BT2
Cell in the contact circuit
R1
Resistor in the contact circuit

Questions on Fig. 10

  1. Which two external wire nodes touch coil terminals A1 and A2?

    Check the answer

    One node joins BT1 + to A1; another joins A2 back to BT1 −. ⁠Source 1Source 2

  2. Does any contact-side conductor join a coil-side conductor?

    Check the answer

    No. No wire links A1 or A2 to COM, NC or NO, so the coil circuit and the contact circuit share no node. ⁠Source 11Source 12

  3. Which contact terminal ends without another component attached in this drawing?

    Check the answer

    NO. Its wire runs out to the right and stops; no other part is on that node. ⁠Source 1Source 2

Every convention on one drawing

  • A small relay circuit, drawn at rest with no values, its conventions numbered: the reference designators, two +5 V supply stubs, a junction dot, wires crossing with no dot, the signal-reference symbol with its 0 V label, and the relay's dashed mechanical link
  • A small relay circuit, drawn at rest with no values, its conventions numbered: the reference designators, two +5 V supply stubs, a junction dot, wires crossing with no dot, the signal-reference symbol with its 0 V label, and the relay's dashed mechanical link
1 Reference designators
As in rule 1.
2 Short labelled stub
As in rule 4.
3 Dashed line
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.⁠Source 9Source 13
4 Cross with no dot
In the newer convention used here, wires that cross with no dot are not connected. Older schematics drew connected wires as a plain crossing and made unconnected wires hop over each other with a small half-circle, so check a drawing's legend.⁠Source 3
5 Signal-reference symbol
The signal-reference symbol marks the chosen zero-volt reference for circuit voltages. It need not be connected to earth or chassis.⁠Source 1Source 14
6 0 V
As in rule 4.
7 Dot
As in rule 2.
  • A small relay circuit in IEC style, drawn at rest with no values, its conventions numbered: the reference designators, two +5 V supply stubs, a junction dot, wires crossing with no dot, the signal-reference symbol with its 0 V label, and the relay's dashed mechanical link
  • A small relay circuit in IEC style, drawn at rest with no values, its conventions numbered: the reference designators, two +5 V supply stubs, a junction dot, wires crossing with no dot, the signal-reference symbol with its 0 V label, and the relay's dashed mechanical link
1 Reference designators
As in rule 1.
2 Short labelled stub
As in rule 4.
3 Dashed line
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.⁠Source 9Source 13
4 Cross with no dot
In the newer convention used here, wires that cross with no dot are not connected. Older schematics drew connected wires as a plain crossing and made unconnected wires hop over each other with a small half-circle, so check a drawing's legend.⁠Source 3
5 Signal-reference symbol
The signal-reference symbol marks the chosen zero-volt reference for circuit voltages. It need not be connected to earth or chassis.⁠Source 1Source 14
6 0 V
As in rule 4.
7 Dot
As in rule 2.
Fig. 11 — A relay circuit drawn at rest, values left off, with its drawing conventions numberedA relay circuit drawn at rest, values left off, with its drawing conventions numbered

Notes

  1. A schematic describes electrical connections only, not where parts sit. Parts can be moved or redrawn anywhere on the page without changing the circuit, as long as every connection is kept.⁠Source 1
  2. 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 11Source 15

Check your reading

More questions on the practice page

Pick an answer to see the reason.

  1. Question 1

    In the torch circuit, are the cell's + terminal and the lamp's lower terminal on the same node?

    BT1S1DS1

    One loop of wire. On the left is a cell labelled BT1, drawn upright with its long line at the top. The wire from the top of the cell runs to a switch labelled S1 along the top, drawn open, and on to the top of a lamp labelled DS1, a circle with a cross, on the right. The wire from the bottom of the lamp runs along the bottom back to the bottom of the cell.

    BT1S1DS1

    One loop of wire. On the left is a cell labelled BT1, drawn upright with its long line at the top. The wire from the top of the cell runs to a switch labelled S1 along the top, drawn open, and on to the top of a lamp labelled DS1, a circle with a cross, on the right. The wire from the bottom of the lamp runs along the bottom back to the bottom of the cell.

    Not this one Right Answer

    The answer is “No: the switch and the lamp sit between them”. In the ideal-wire schematic model, a node is the set of points connected by uninterrupted wire. Those points share one potential; real wire resistance and other wire effects are omitted.

  2. Question 2

    These two wires cross with no dot. In the convention used here, are they connected?

    Two straight wires crossing at right angles, one horizontal and one vertical, with no dot where they cross.

    Not this one Right Answer

    The answer is “No: without a dot they are not connected”. A small half-circle hop where one wire passes over another also means the wires are not connected. Some drawings put a hop at every unconnected crossing and a dot at every connection, so neither is left to guess. In the newer convention used here, wires that cross with no dot are not connected. Older schematics drew connected wires as a plain crossing and made unconnected wires hop over each other with a small half-circle, so check a drawing's legend.

  3. Question 3

    A part on a schematic is labelled K1. What kind of part is it?

    Not this one Right Answer

    The answer is “A relay”. Reference designators identify parts with class letters and a number. Common letters used here are R resistor, C capacitor, D diode, Q transistor, L inductor, T transformer, S switch, K relay and F fuse; other naming systems exist.

  4. Question 4

    Two stubs on the same schematic are both labelled +5 V, with no wire between them. Are they the same node?

    Not this one Right Answer

    The answer is “Yes: stubs with the same label are one node”. Within the drawing's stated scope, repeated supply or reference labels identify the same node without a drawn wire between them. Different labels or reference symbols must not be assumed connected.A schematic describes electrical connections only, not where parts sit. Parts can be moved or redrawn anywhere on the page without changing the circuit, as long as every connection is kept. A supply connection is often drawn as a short labelled stub or dot, such as +5 V, VCC or VDD, instead of a wire back to the source. The source's other side is taken to be the ground reference, and every stub with the same label is the same node.

  5. Question 5

    A resistor on a schematic is labelled 4k7. What value does that give?

    Not this one Right Answer

    The answer is “4.7 kΩ”. Values printed beside a symbol may put the multiplier letter where the decimal point would be: 4k7 means 4.7 kΩ, 3R9 means 3.9 Ω, 47R means 47 Ω and 2M2 means 2.2 MΩ. IEC 60062 sets out this letter code.

Answer key

  1. 1

    No: the switch and the lamp sit between them

  2. 2

    No: without a dot they are not connected

  3. 3

    A relay

  4. 4

    Yes: stubs with the same label are one node

  5. 5

    4.7 kΩ

Questions

Do crossing wires connect?
Not where they cross without a dot. A dot joins them, and wires that meet in a T are joined with or without one. Older drawings may follow another rule, some using a small hop for wires that do not connect, so check the legend.⁠Source 1Source 3Source 9
What does R1 or K1 mean?
It is a reference designator: the letters give the kind of part and the number tells parts of that kind apart. R is a resistor and K a relay.⁠Source 4
Why are ground and supply labels not joined by wires?
A repeated label stands in for the wire. Within the drawing's scope, every mark with the same label, such as +5 V or GND, is the same node; marks with different labels are not assumed to be joined.⁠Source 1Source 5Source 10

Sources

15 sources, numbered as cited
  1. Electrical Schematics, §§1.3.1–1.3.5 — nodes, crossings, references and congruent drawings

    Tufts University, retrieved 2026-09-22.

  2. ModEL — Sources and Loads, Voltmeters and Ammeters, §§4.2–4.6 and §6.2

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

  3. Lessons In Electric Circuits, Vol. V — §9, Circuit Schematic Symbols (pp. 130–139)

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

  4. 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

  5. DC Electrical Circuit Analysis — resistive devices and schematic ground symbols (pp. 53, 59–64)

    James M. Fiore, Mohawk Valley Community College, retrieved 2026-09-22.

  6. ModEL — Ohm’s and Joule’s Laws, Resistor Ratings, and Electrical Safety, §6.2 (resistor labelling, p. 73)

    Tony R. Kuphaldt, retrieved 2026-09-23. a letter is used in place of a decimal point, the letter either being R (unit), K (kilo), M (mega), G (giga), T (tera), or L (milli). This is commonly referred to as the RKM code.

  7. IEC 60062:2016+AMD1:2019 — Marking codes for resistors and capacitors; public preview contents (preview p. 3)

    International Electrotechnical Commission, retrieved 2026-09-23. 4 Letter and numeral code for resistance and capacitance values … 4.2.1 The RKM code system … 4.3.1 The multiplier code system for capacitors

  8. ModEL — Components and Symbols, §4.3 (capacitor labelling, p. 49)

    Tony R. Kuphaldt, retrieved 2026-09-23. a lower-case letter “p” may be used as a decimal point; e.g. 2p2 would be 2.2 picoFarads. Similarly, the lower-case letter “n” may be used as a decimal point as well

  9. 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

  10. ModEL — Semiconductor Logic Gates, §3.4 (supply terminal labels VCC, VEE, VDD and VSS, p. 43)

    Tony R. Kuphaldt, retrieved 2026-09-23. On the bipolar gate the positive power supply terminal is labeled VCC because it is on the side of every transistor’s collector terminal

  11. ModEL — Electromechanical Relays, §§3.2–3.3 and §5.1 (normal and present contact status)

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

  12. Relay technology — structure, operation and contact forms

    Omron, retrieved 2026-09-22.

  13. 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.

  14. Where Is Ground? — local reference versus earth

    Analog Devices, retrieved 2026-09-22.

  15. 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).