A relay symbol represents an electromechanical or solid-state switch controlled by an electromagnetic coil. Because schematics are the universal language of electrical work, misinterpreting these symbols leads to miswired control circuits, blown fuses, or damaged PLC outputs. The two dominant global standards you will encounter are IEC 60617 (International/European) and ANSI/IEEE 315 (North American). Below is the direct reference data you need to read, wire, and troubleshoot relay circuits accurately.
The Complete Relay Symbol & Pinout Reference Table
The table below maps the most common relay components to their schematic representations and physical pinouts. Note that IEC standards typically separate the coil and contacts spatially on the drawing, linking them with a dashed line or alphanumeric tag (e.g., K1), while ANSI often groups them more closely.
| Component / Function | IEC 60617 Symbol Description | ANSI/IEEE 315 Symbol Description | Common Pin Mapping (8-Pin / 14-Pin) |
|---|---|---|---|
| Standard Coil | Rectangle with diagonal lines or empty rectangle labeled 'K' | Circle or rectangle with 'CR' (Control Relay) inside | 8-pin: 2 & 7 14-pin: 13 & 14 |
| Polarized / Latching Coil | Rectangle with a permanent magnet symbol (crossed box) or latch indicator | Circle with a magnetic latch indicator or 'L' designation | Varies by manufacturer (e.g., Omron G2RK uses specific set/reset pins) |
| NO Contact (Form A) | Two parallel lines, one with a hinged diagonal line pointing away | Two parallel lines, one with a hinged line pointing away, often marked 'NO' | 8-pin: 1 & 3 14-pin: 1 & 9 |
| NC Contact (Form B) | Two parallel lines, one with a hinged diagonal line crossing over | Two parallel lines, one with a hinged line crossing over, marked 'NC' | 8-pin: 1 & 4 14-pin: 1 & 11 |
| Changeover (Form C) | Combination of NO and NC sharing a common pivot point | Combination of NO and NC sharing a common pivot, marked 'COM' | 8-pin: 1, 3, 4 14-pin: 1, 9, 11 |
| Time-Delay (On-Delay) | Standard coil symbol with an 'X' or hourglass inside, or 'ON' arrow | Circle with a clock face or 'TD' designation, arrow pointing up | Typically 8-pin base, pins match standard Form C layout |
| Time-Delay (Off-Delay) | Standard coil symbol with an inverted arrow or 'OFF' designation | Circle with clock face, arrow pointing down | Typically 8-pin base, pins match standard Form C layout |
Regional Standard Variants: IEC vs. ANSI vs. Legacy UK
When searching for a specific symbol relay chart, the first step is identifying which regional standard the schematic was drawn under. Mixing these up is a primary cause of troubleshooting errors in imported machinery.
IEC 60617 (International / European / Modern Global)
The IEC standard treats a relay as a collection of separate functional blocks. The coil is drawn in the control circuit, and the contacts are drawn in the power or logic circuit, sometimes pages apart. They are linked purely by an alphanumeric designator (e.g., coil K1 operates contact K1). This keeps complex schematics uncluttered but requires you to trace tags across multiple pages.
ANSI/IEEE 315 (North America)
North American schematics traditionally use the ANSI/IEEE 315 (formerly ANSI Y32.2) standard. Here, relay coils are often drawn as circles containing letters like CR (Control Relay), M (Motor Starter), or T (Timer). Contacts are drawn using the 'ladder logic' format, with vertical power rails and horizontal rungs. The physical proximity of the coil and its contacts on the drawing is often closer than in IEC drawings.
Legacy BS (British Standard / Old UK)
Before harmonizing with IEC, the UK used BS 3939. You will still see this in older British industrial panels. It uses a mix of pictorial representations (drawing the actual physical outline of the relay) and abstract symbols. If you encounter a relay drawn as a literal rectangle with physical pin numbers printed directly next to the contacts inside the symbol, you are likely looking at a legacy BS or early manufacturer-specific diagram.
When retrofitting or troubleshooting imported CNC machines or packaging equipment, never assume the panel follows local standards. A machine built in Germany will use IEC 60617 and IEC 60446 wire colors (Brown/Blue/Green-Yellow), while a US-built machine uses ANSI and NEC colors (Black/White/Green). Always verify the schematic legend block before probing live terminals.
Rows and Pins People Get Wrong (And How to Fix Them)
Even experienced technicians make specific, repeatable errors when interpreting relay schematics and wiring physical bases. Here are the most common failure points.
1. Misidentifying the Common (COM) Pin on Form C Contacts
The most frequent wiring error occurs on 8-pin "ice cube" relays (like the ubiquitous Omron G2R-2-S or Finder 55.34). Technicians often wire the load to pin 2 or 7, assuming they are the common terminals because they are centrally located. Pins 2 and 7 are almost always the coil on an 8-pin relay. The common pins for the contacts are 1 and 8 (or 1 and 4 on some 14-pin layouts). Always verify the pinout diagram printed on the side of the physical relay housing, not just the schematic.
2. Confusing Solid-State Relay (SSR) Symbols with Electromechanical
An SSR symbol does not use a coil and hinge representation. Instead, the IEC symbol for an SSR features an input side drawn as an LED/diode symbol inside a box, and an output side drawn as a TRIAC or MOSFET symbol, separated by an optical isolation barrier (usually two small arrows pointing away from each other). If you wire an AC load to the DC control pins of an SSR because you misread the symbol as a standard coil, you will instantly destroy the internal optocoupler.
3. Safe Interpretation When Markings are Faded or Missing
In harsh industrial environments, the pinout diagrams printed on relay housings fade, melt, or get painted over. Never guess the pinout based on physical placement alone. Use this safe verification procedure:
- De-energize and Lockout: Turn off the control power, apply LOTO, and verify the circuit is dead using a CAT III or CAT IV multimeter.
- Identify the Coil: Set your multimeter to the Ohms (Ω) setting. Probe pairs of pins. The coil will typically read between 50Ω and 800Ω (for 12V to 120V DC coils). If you read infinite resistance (OL), it is not the coil (or the coil is burnt open). If you read near 0Ω, you are measuring a closed contact.
- Identify Contacts: Switch the meter to Continuity mode. Manually press the relay's test button (if equipped) or use a bench power supply to briefly energize the coil. Listen for the click and observe which pins transition from open (OL) to closed (continuity) to map the NO and NC contacts.
Relay Symbol and Wiring FAQs
What does the dashed line mean in a relay symbol?
In both IEC and ANSI schematics, a dashed or dotted line connecting a coil symbol to a contact symbol (or connecting multiple contacts together) represents a mechanical linkage. It indicates that when the coil is energized, the physical armature moves and actuates all the contacts connected by that dashed line simultaneously. In IEC drawings where the coil and contacts are separated by distance on the page, the dashed line is often replaced by an alphanumeric cross-reference tag (e.g., '/K1.3' meaning page K, column 1, line 3).
How do I identify a relay coil symbol if the schematic has no legend?
If you are handed an unmarked legacy schematic, look for the standard alphanumeric designators. In IEC, coils are almost always designated with K (e.g., K1, K2). In ANSI/NEMA ladder logic, control relays are CR, motor starters are M, and timing relays are TR or T. The symbol itself will be a rectangle (IEC) or a circle (ANSI) placed directly across the two control power rails (L1 and L2, or +24V and 0V).
Why do IEC and ANSI relay symbols look completely different?
The divergence stems from historical drafting philosophies. ANSI/NEMA developed alongside the US motor control industry, prioritizing "ladder logic" where the physical layout of the drawing mimics the physical flow of power from top to bottom. IEC developed later with a focus on functional modularity; it separates the function of the component from its physical location, allowing a single relay's contacts to be drawn across three different pages of a complex PLC schematic without cluttering the drawing with long, crossing lines.
What is the symbol for a time-delay relay, and how do I read the timing arrow?
A time-delay relay symbol includes the standard coil representation but adds a timing indicator. An On-Delay (Delay-on-Energize) symbol features an arrow pointing upward or toward the contact, indicating the delay happens as the coil receives power. An Off-Delay (Delay-on-De-energize) symbol features an arrow pointing downward or away from the contact, indicating the delay happens when power is removed. Always verify the exact timing function (e.g., Interval, One-Shot, Repeat Cycle) in the manufacturer's datasheet, as schematic symbols for advanced timing functions can vary wildly between brands like Macromatic and Schneider Electric.
Can I use an AC coil symbol interchangeably with a DC coil symbol?
Schematically, the basic coil symbol is often identical for AC and DC. However, some detailed schematics will add a sine wave (~) inside or next to the rectangle for AC, and a solid line with a dashed line beneath it (⎓) for DC. Physically, they are not interchangeable. An AC relay coil relies on inductive reactance to limit current; if you apply DC to it, the coil will draw excessive current and burn out. Conversely, a DC relay coil relies on wire resistance; if you apply AC, it will chatter violently and overheat due to eddy currents, unless it has a built-in rectifier bridge.
