Complete Solenoid Coil Symbol Reference Table
Use this table to identify the specific solenoid coil symbol on your schematic. Device tags and visual representations vary strictly by the governing standard body.
| Standard Body | Symbol Name | Visual Description | Typical Device Tag | Primary Region |
|---|---|---|---|---|
| IEC 60617 | Standard Solenoid | Empty rectangle | Y1, Y2, SOL1 | Europe, Global, Modern US |
| IEC 60617 | Latching Solenoid | Rectangle with a diagonal slash | Y1L, Y2L | Europe, Global |
| IEC 60617 | Proportional Solenoid | Rectangle with a diagonal arrow inside | Y1P, PROP1 | Global (Fluid Power) |
| NEMA ICS 19 | Standard Solenoid | Circle or hatched rectangle | SOL, S1 | US Industrial / Legacy |
| IEEE 315 / ANSI | Solenoid / Actuator | Rectangle with diagonal lines or 'S' label | S1, ACT1 | US Electronics / Schematics |
| BS 3939 (Legacy) | Solenoid Coil | Circle with a solid center dot | SOL | Old UK (Pre-1990s) |
Regional and Standard Variants: Which Applies to You?
When reading a schematic, the first step is identifying the drafting standard. Mixing up IEC and NEMA symbols can lead to catastrophic wiring errors, particularly when dealing with 120V AC versus 24V DC control circuits.
IEC 60617 (Global & Modern Standard)
The IEC 60617 standard dominates modern global automation, including newer US facilities built by European OEMs. IEC relies heavily on alphanumeric device tags rather than changing the shape of the symbol. A standard solenoid and a standard relay coil might both look like an empty rectangle; the difference is entirely in the prefix letter. Solenoids use 'Y' (or sometimes 'S' in fluid power), while relays use 'K'. Always trace the mechanical linkage line (a dashed line) exiting the rectangle to confirm it actuates a valve, clutch, or linear pin rather than electrical contacts.
NEMA and Legacy US Industrial
NEMA standards, widely used in older US manufacturing plants and heavy machinery, often depict a solenoid coil as a circle or a rectangle with distinct internal hatching. The NEMA standards directory outlines these legacy conventions. If you are working on a machine built in the US before 2005, expect to see circular coil symbols. NEMA schematics also frequently draw the solenoid coil directly in series with the limit switch or pushbutton on the line diagram, rather than separating the logic and power circuits like IEC ladder logic does.
IEEE 315 / ANSI Y32.2 (US Electronics)
For bench-level electronics, PCB schematics, and aerospace wiring diagrams in the US, the IEEE 315 standard applies. Here, solenoids are often drawn as rectangles with a diagonal strike-through or labeled explicitly with an 'S' inside the box to differentiate them from inductors (which use standard coil humps) and relays.
The 'Rows People Get Wrong' Notes
Even experienced technicians misread specific solenoid variations. Pay close attention to these common schematic traps:
- Missing the Latching Slash: In IEC schematics, a diagonal slash through the solenoid rectangle indicates a magnetic latching solenoid. Unlike a standard spring-return solenoid that requires continuous power to hold, a latching solenoid only needs a momentary pulse to change state, and a reverse-polarity pulse to reset. If you wire a continuous 24V DC hold to a latching solenoid, you will burn out the coil in minutes.
- Confusing AC Shading Rings: AC solenoids require a copper shading ring to prevent the armature from chattering at the zero-crossing of the AC sine wave. On detailed schematics, an AC solenoid coil symbol will feature a short parallel line or a specific hatch mark next to the rectangle. If you replace a symbol-matched AC solenoid with a DC equivalent, the coil will draw massive current and fail, or the valve will hum violently.
- Proportional vs. On/Off: A proportional solenoid (rectangle with a diagonal arrow) requires a PWM driver or a dedicated proportional amplifier card. Wiring it directly to a standard 24V DC relay output will result in the valve slamming open at 100% flow, completely defeating the purpose of the proportional control loop.
- Relay vs. Solenoid Tags: Never assume a rectangle is a relay just because it is in the control circuit. Always check the tag. 'K1' is a relay. 'Y1' is a solenoid. 'M1' is a motor contactor.
Safe Interpretation When Markings Are Faded or Missing
On legacy equipment, thermal transfer prints, or oil-stained blueprints, the device tags and internal symbol hatching often fade away. If you are left staring at a generic rectangle or circle, use this three-step bench verification process to safely determine if it is a solenoid coil or a relay coil before applying power.
- Trace the Mechanical Linkage: Look for a dashed or dotted line extending from the symbol. In both IEC and NEMA, a dashed line indicates a mechanical action. If that line terminates at a valve box (usually a square with arrows indicating flow paths), a brake, or a clutch, the coil is a solenoid. If the line terminates at a bank of electrical contacts (normally open/closed switches), it is a relay or contactor.
- Check the Upstream Protection: Look at the fuse or circuit breaker feeding the branch circuit. Control relays typically draw 20mA to 100mA. A branch circuit protected by a 0.5A or 1A fuse likely feeds relays. A branch circuit protected by a 3A, 5A, or 10A breaker is almost certainly feeding solenoids, which have high inrush currents (often 5 to 10 times their holding current) when the air gap is open.
- Measure the Coil Resistance: De-energize and lock out the panel. Disconnect one wire from the coil terminal and measure resistance with a multimeter. A standard 24V DC control relay coil will typically read between 800 ohms and 2.5k ohms. A 24V DC pneumatic solenoid coil will usually read between 15 ohms and 60 ohms. If your reading is in the low double digits, you are dealing with a solenoid.
Frequently Asked Questions
What is the difference between a solenoid coil symbol and a relay coil symbol?
In IEC 60617, the physical shape of the symbol (a rectangle) is identical for both. The difference lies in the alphanumeric device tag and the mechanical linkage. A relay coil is tagged with a 'K' (e.g., K1, K2) and its dashed mechanical line points to electrical switch contacts. A solenoid coil is tagged with a 'Y' (e.g., Y1, Y2) and its dashed line points to a mechanical device like a hydraulic valve spool, a pneumatic cylinder, or a physical latch.
How do you identify an AC solenoid coil symbol on a schematic?
On detailed schematics, an AC solenoid is indicated by a specific notation next to or inside the standard coil rectangle. This is often a short parallel line representing the copper shading ring, or the letters 'AC' explicitly written inside the box. Additionally, the power supply rails feeding the coil will be labeled with an AC voltage (e.g., 120V AC, 24V AC) and typically lack the flyback diode symbols that are mandatory for DC solenoid circuits.
What does a diagonal line through a solenoid coil symbol mean?
A diagonal line (slash) through the solenoid rectangle designates a latching or bistable solenoid. Unlike a standard monostable solenoid that requires continuous voltage to remain actuated and relies on a spring to return, a latching solenoid uses a permanent magnet or a mechanical detent to hold its position. It only requires a brief electrical pulse to change states, making it ideal for battery-operated systems or fail-safe applications where power loss must not change the valve state.
How is a proportional solenoid valve represented in IEC schematics?
A proportional solenoid is represented by the standard IEC rectangle, but it features a diagonal arrow drawn inside the box, or sometimes an arrow pointing into the side of the rectangle. This indicates that the solenoid's physical displacement (and thus the valve's flow rate) is directly proportional to the applied current or voltage, rather than being a simple binary on/off device. It signals to the technician that a proportional amplifier card or PWM output is required, not a standard discrete digital output.
