Coil Electrical Symbol Reference Chart: IEC, ANSI & Relay Pinouts

A coil electrical symbol represents a wound conductor designed to store energy in a magnetic field, filter frequencies, or actuate a mechanical switch. Because a coil can function as an inductor, a relay, a solenoid, or a transformer winding, the exact schematic symbol changes based on its specific job and the regional drafting standard (IEC vs. ANSI) used by the engineer. Below is the definitive bench reference for identifying, distinguishing, and testing these components in the wild.

Master Coil Electrical Symbol Reference Chart

Use this table to cross-reference the schematic symbol you are looking at with its physical real-world counterpart. The designators and resistance values provided are benchmarks for typical 12V to 120V control and power circuits.

Regional Standard Variants: IEC 60617 vs ANSI Y32.2

Before you can accurately read a coil symbol, you must identify which drafting standard the schematic follows. Mixing these up is the primary cause of miswiring control panels.

IEC 60617 (International / European / Modern Global): The International Electrotechnical Commission favors orthogonal, block-based geometry. Under IEC rules, a relay coil is almost always drawn as a simple rectangle. To prevent confusion with a resistor (which is also a rectangle under IEC), the relay coil rectangle will typically feature a diagonal line through it, or it will be explicitly labeled with a 'K' designator. Inductors and transformer windings retain the classic semi-circle 'humps', but the overall aesthetic of the schematic will be rigid and grid-aligned. If you are working on modern PLC panels, VFD enclosures, or equipment imported from the EU or Asia, expect IEC symbols.

ANSI/IEEE 315 & NEMA (North American / Legacy Industrial): North American standards historically relied heavily on circles and pictorial representations. An electromechanical relay coil is frequently drawn as a circle, sometimes with a diagonal line or an 'M'/'CR' (Control Relay) inside. Inductors use the same semi-circle humps as IEC, but older US schematics might draw transformer windings with loops rather than distinct humps. If you are troubleshooting a legacy US industrial panel built before the early 2000s, or dealing with NEMA-rated motor starters, you will encounter ANSI symbols.

Legacy UK BS 3939: While largely superseded by IEC 60617, you may still encounter BS 3939 in older British infrastructure. It heavily utilized circles for relays and specific loop notations for inductors. Treat these as you would ANSI, but verify the title block for regional origin.

For a deeper look into how magnetics behave in these circuits, review the foundational physics outlined by Analog Devices in their inductor basics guide, which bridges the gap between the schematic symbol and the physical magnetic field.

The "Rows People Get Wrong" and Safe Schematic Interpretation

When schematics are faded, poorly photocopied, or entirely missing, relying purely on visual memory of symbols leads to costly mistakes. Here are the most common misreads and the exact multimeter protocols to verify what you are actually looking at.

Misread 1: The IEC Relay Rectangle vs. The IEC Resistor

Because both are drawn as rectangles in IEC 60617, a faded diagonal line on a relay coil can make it look exactly like a standard resistor. The Fix: Look at the parallel wiring. A resistor is almost always in series with a load or in a voltage divider network. A relay coil will be wired directly across a DC supply (e.g., 12V or 24V) and a ground, usually driven by a transistor or PLC output. Furthermore, a resistor will read exact ohms on a DMM and exhibit no magnetic properties, whereas a relay coil will read a specific low resistance (e.g., 288Ω for a 12V Omron G5V-2) and will audibly click when energized.

Misread 2: Transformer Windings vs. Chokes

A single set of humps is a choke (inductor). Two sets of humps side-by-side with a line in the middle is a transformer. However, in tightly packed schematics, the core line is sometimes omitted, making a transformer primary look like a standalone inductor. The Fix: Check the node connections. An inductor has two terminals and passes DC. A transformer winding will have two terminals, but it will read as a near-dead short on a multimeter's DC resistance setting (often less than 1Ω for high-current secondaries) while completely blocking DC current in a live circuit. For more on testing magnetics safely, consult Fluke's field guide on inductor testing.

Safe Verification Protocol for Faded or Unmarked Coils

When you must reverse-engineer a board or panel without documentation, follow this DMM sequence to safely identify the coil type without blowing your meter's internal fuse:

1. De-energize and Discharge: Lock out the power source. Wait 5 minutes for large capacitors to bleed off. Coils themselves do not store voltage, but the circuits they inhabit often do.
2. Measure DC Resistance (DCR): Set your multimeter to the lowest Ohms range.
   • Reading 0.0Ω to 1Ω: Likely a high-current transformer secondary, a heavy solenoid, or a shorted inductor.
   • Reading 10Ω to 500Ω: Typical for control relay coils (e.g., 24VDC ice-cube relays usually sit between 400Ω and 1000Ω; 12V automotive relays sit around 75Ω).
   • Reading OL (Open Line): The coil wire is snapped internally, or an internal thermal fuse has blown. The component is dead.
3. Check for Inductance (if meter supports it): Switch to the Henry (H) setting. A true inductor/choke will read in microhenries (µH) or millihenries (mH). A relay coil will also show inductance, but its primary function is resistive actuation.