[ SINGLE LINE DIAGRAM SYMBOLS · STANDARD ]
ANSI single line diagram symbols
US one-line diagrams use the symbols of IEEE 315, also published as ANSI Y32.2, and name protective functions with the device numbers of IEEE C37.2. The result looks different from an IEC drawing: breakers are boxes marked 52, relays are circles with numbers such as 50/51, and low voltage breakers are arcs.
- Symbol standard
- IEEE/ANSI 315-1975, Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters)
- Status
- Reaffirmed 1993, Inactive-Reserved since November 2019. Still the reference for US drawing practice
- Earlier name
- ANSI Y32.2, first published as USA Standard Y32.2-1967
- Device numbers
- IEEE C37.2-2022: 95 device function numbers and 22 acronyms
- Used in
- The US, much of the Americas and projects that follow US practice
Sources and machines ANSI / IEEE
About sources and machinesTransformers ANSI / IEEE
About transformersSwitching devices ANSI / IEEE
About switching devicesProtection and metering ANSI / IEEE
About protection and meteringBusbars and connections ANSI / IEEE
About busbars and connectionsLoads and power electronics ANSI / IEEE
About loads and power electronicsWhat sets ANSI one-lines apart
- Medium voltage circuit breakers are a square in the line, often marked 52, the device number for an AC circuit breaker. Draw-out breakers add a chevron on each side.
- Low voltage breakers are a curved arc between two contacts, with frame and trip ratings beside them.
- Protective relays are circles with the device numbers of their functions: 50/51 overcurrent, 87T transformer differential, 27/59 under and overvoltage.
- Fuses are often an S-shaped curve, and contactors two parallel lines marked M.
- Transformers are drawn as two facing coils or as two overlapping circles. Both are common.
Side by side drawings of every symbol are on the IEC vs ANSI comparison.
About this legend
IEEE 315 allows several forms for many symbols, and companies add their own. The drawings here are the forms most common on US one-line diagrams. The legend sheet of the project drawing set is always the final word.
Frequently asked questions
What are ANSI electrical symbols?
The graphic symbols of IEEE 315, also published as ANSI Y32.2, used on US electrical drawings. On one-line diagrams they are combined with the ANSI device numbers of IEEE C37.2 to name protective functions.
Is IEEE 315 still valid?
IEEE 315-1975 was reaffirmed in 1993 and has been Inactive-Reserved since November 2019. It is no longer maintained, but it remains the reference for US drawing practice.
How is a circuit breaker drawn on an ANSI one-line?
Medium voltage breakers are a square in the line, often marked 52. Low voltage breakers are a curved arc between two contacts.
What does 52 mean on a single line diagram?
52 is the ANSI device number for an AC circuit breaker. See the full list of ANSI device numbers.
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The symbols on this page were drawn by Deskely and are free to use. Standards are revised and every project issues its own legend sheets, which take precedence.