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Two small circles of the same size on a circuit diagram, one filled and one hollow, meaning a permanent joint and a connection point.
A filled dot where conductors meet means they are joined; a hollow circle means a terminal, a point where an external conductor may be attached. The two are drawn the same size and differ only in whether the interior is inked, which is exactly why careful drafting avoids four-way crossings altogether and staggers them into two three-way junctions — a dot that is smudged, lost in reproduction or added by mistake changes the circuit rather than the drawing.
Filled means a joint; hollow means a terminal.
Drawn from the visual attributes recorded for each symbol. Only traits the two records disagree about are listed.
| Trait | Junction dot | Terminal symbol |
|---|---|---|
| Built from | lines and dots | circles |
| Junction dot | Terminal symbol | |
|---|---|---|
| Interior | Filled solid. | Left open. |
| What it asserts | The crossing conductors are electrically joined. | An external connection may be made here. |
| If it is missing | The conductors are read as crossing without touching. | The connection point is not offered to the reader at all. |
| Relationship (from Symbolwise's records) | Commonly confused with Terminal symbol — Filled means a joint; hollow means a terminal. | Commonly confused with Junction dot — Hollow means a terminal; filled means a joint. |
IEC 60617, Graphical symbols for diagrams
International Electrotechnical Commission · retrieved 2026-08-22
Maintained as an online database and NOT READ in full. Registered so a circuit-diagram record can say which body defines its symbol, and so the divergence between the IEC form and the older American form can be recorded as a real standards difference rather than a drawing preference. See docs/paywalled-standards.md.
ANSI Y32.2 / IEEE 315, Graphic Symbols for Electrical and Electronics Diagrams
IEEE / American National Standards Institute · retrieved 2026-08-22
Paywalled and NOT READ in full. Registered so the zig-zag resistor familiar from American schematics can be attributed to the standard that defines it, rather than described as the 'old' or 'wrong' form. See docs/paywalled-standards.md.
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the component is, how its symbol is conventionally drawn, and where the ANSI and IEC conventions differ. Not used for any claim about the text of IEC 60617, which is paywalled and was not consulted.
Alpha is a Greek letter and stands for a quantity — an angle, a coefficient, a significance level. The proportionality sign is an operator and stands between two quantities to say they keep a constant ratio. The drawings differ in that the proportionality sign's right-hand stroke runs out in an open curve rather than closing into the letter's tail.
Look at the left-hand edge. A straight flat back is an AND gate: the output is true only when every input is. A curved concave back is an OR gate: true when any input is. Everything else about the shapes is similar, which is why the back edge is worth checking deliberately rather than at a glance.
Equal-length lines mean a capacitor. Alternating long and short lines mean a battery, with the long line positive. If the second line is curved rather than straight it is a polarised capacitor — still a capacitor, but one that must be fitted the right way round.
Look at the pattern. Even short dashes throughout is a hidden line: an edge that exists but is concealed behind material. Long dashes alternating with dots is a centre line: an axis of symmetry or the centre of a circle, which is not a physical edge at all. Reading a centre line as an edge is the commonest beginner's error on a drawing.