Electrical Schematic Symbols and Abbreviations
Identify common circuit symbols, contact states, instrument marks, and drawing abbreviations using a visual legend with context and notation limits.
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Visual symbol legend
Use this legend for common circuit and control schematics and instrument marks. It is not a complete architectural floor-plan symbol standard. Symbol styles vary between drawing systems, manufacturers, and project legends.
| Symbol | Name | How to read it |
|---|---|---|
| Resistor, zigzag style | A resistive component; do not interpret the zigzag as conductor routing. | |
| Resistor, rectangular style | Another common schematic convention; use the drawing legend to choose the notation. | |
| Capacitor, unpolarized symbol | Does not identify capacitance, voltage rating, or polarity of a particular device. | |
| Normally open contact | Drawn open in the stated normal condition; an operating action closes it. | |
| Normally closed contact | Drawn closed in the stated normal condition; an operating action opens it. | |
| Relay / contactor coil, rectangular style | Associated contacts may be drawn elsewhere and linked by device identification. | |
| Earth / ground reference | A ground symbol requires context; it does not by itself specify a protective conductor size. | |
| Chassis / frame connection | A connection to a frame or chassis; not automatically the same node as every ground reference. | |
| Direct current / DC quantity | A straight line above a dashed line; a measurement-mode mark, not a wiring terminal number. | |
| Alternating current / AC quantity | A sinusoidal mark identifying an AC quantity or mode. | |
| Battery / DC source | Unequal plates identify a source symbol; read the polarity and rating labels on the actual drawing. | |
| Fuse, one common style | A protective component; its time-current characteristic is not specified by this symbol. | |
| Connected conductors | A connection dot explicitly joins the conductors. | |
| Crossing without connection, bridge style | The bridge shows one conductor passing another without a junction. |
Common drawing abbreviations
| Abbreviation | Common meaning | Context to confirm |
|---|---|---|
| NO / NC | Normally open / normally closed | The defined normal condition, including latching or trip state. |
| COM | Common terminal | Not necessarily a neutral or ground. |
| PE | Protective earth | Protective bonding function and the applicable drawing convention. |
| N | Neutral | The system drawing and the actual grounded-conductor function. |
| L1 / L2 / L3 | Line or phase identifiers | System voltage and phase sequence must be established separately. |
| TB | Terminal block | Numbered terminals and cross-reference to the terminal schedule. |
| M | Motor in many drawings | The project device tagging convention. |
| OL | Overload on many control drawings; over-limit on some instruments | The same abbreviation has different meanings on a meter and a motor-control diagram. |
Read the drawing context
- Start with the project legend, drawing type, revision, and scope.
- Identify the normal state used for contacts and the cross-references linking a coil to its contacts.
- Check labels at crossing conductors. An explicit bridge means no connection; a junction dot means connected. A crossing without either convention needs the drawing legend.
- Separate symbols, device tags, terminal numbers, and ratings. None substitutes for the others.
The graphics above are original simplified illustrations of common conventions. The Fluke manual supplies instrument-mark examples; ABB documentation supplies contact and coil context. Use the exact product schematic for a connection decision.
Continue with terminal markings or the mechanical switch topology diagrams.