[ ELECTRICAL SYMBOLS · STANDARD ]
ANSI electrical symbols (IEEE 315)
IEEE 315, also published as ANSI Y32.2, is the US standard for graphic symbols on electrical and electronics diagrams. It is the reason US schematics draw resistors as zigzags and ladder diagrams draw contacts as two parallel lines.
- Full title
- IEEE 315, Graphic Symbols for Electrical and Electronics Diagrams (including reference designation letters)
- Also published as
- ANSI Y32.2 and CSA Z99
- Edition
- IEEE 315-1975, reaffirmed, with the supplement IEEE 315A-1986
- Used on
- US and Canadian schematics, ladder diagrams and one-lines
- Reference designators
- Letters such as R, C, L, Q, K, CR, CB, FU and M, by company and industry practice
Passive components IEEE 315
About passive componentsSemiconductors IEEE 315
About semiconductorsSwitches and relays IEEE 315
About switches and relaysPower, protection and ground IEEE 315
About power, protection and groundLoads, meters and wiring IEEE 315
About loads, meters and wiringHow US schematics draw things
- A resistor is a zigzag, and a fuse an S-curve or a rectangle.
- On ladder diagrams a normally open contact is two parallel lines, a normally closed contact adds a diagonal, and a relay coil is a circle with its designator.
- Push buttons are drawn with a bridging bar and a plunger: above the terminals for normally open, below them for normally closed.
- Transistors are usually drawn inside a circle.
- Every contact is shown in its normal state, with the coil de-energised and nothing pressed.
Compare each symbol with IEC 60617 on IEC vs ANSI electrical symbols. For power one-lines, see the single line diagram symbols.
Common US reference designators
| Designator | Device |
|---|---|
| R | Resistor |
| C | Capacitor |
| L | Inductor |
| D, CR | Diode (CR also used for diodes in older practice) |
| Q | Transistor |
| CR, K | Control relay |
| M | Motor starter or contactor coil |
| OL | Overload relay |
| PB | Push button |
| SW, S | Switch |
| FU | Fuse |
| CB | Circuit breaker |
| LT, PL | Pilot light |
| T | Transformer |
| TB | Terminal block |
Designators vary by company and industry, and the drawing legend is the final word.
Frequently asked questions
What is IEEE 315?
The US standard for graphic symbols on electrical and electronics diagrams, also published as ANSI Y32.2 and CSA Z99.
Is the ANSI resistor symbol a zigzag?
Yes. IEEE 315 draws a resistor as a zigzag line; IEC 60617 draws it as a rectangle.
How is a relay contact drawn on a US ladder diagram?
A normally open contact is two parallel vertical lines, and a normally closed contact the same with a diagonal line through it. The relay coil is a circle.
Is IEEE 315 still current?
It has been reaffirmed rather than revised, and remains the reference for US schematic symbols, alongside company and industry standards.
- In production since 2014
- Thousands of daily users
- On MODEC FPSO projects since 2016
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.