Contactor Electrical Symbol Guide: IEC, NEMA, and Terminal Pinouts

The contactor electrical symbol represents an electrically controlled, heavy-duty switch used to make or break a power circuit. Unlike a standard control relay, a contactor is engineered to handle high-current loads—typically 15A to over 800A—such as three-phase motors, resistive heating banks, and high-bay lighting. The schematic symbol is universally divided into two functional blocks: the electromagnetic operating coil and the associated switch contacts (main power and auxiliary control).

The Complete Contactor Symbol & Terminal Reference Table

Before wiring or troubleshooting, you must map the schematic symbol to the physical terminal markings on the device. Below is the definitive reference for contactor symbols and their corresponding physical terminal designations under modern standards.

Regional Standard Variants: IEC vs. NEMA vs. Old UK

While the physical operation of a contactor is identical worldwide, the way it is drawn on a schematic and labeled on the chassis depends heavily on the regional standard your facility follows. Applying the wrong standard's logic can lead to miswired control circuits.

IEC 60617 / IEC 60947 (Global, Europe, Modern North America)

The IEC standard uses a rectangle for the coil. The defining feature of IEC is its strict numeric terminal designation system. Main power terminals use single digits (1, 3, 5 for line; 2, 4, 6 for load) or the L/T nomenclature. Auxiliary contacts use a two-digit system where the tens digit indicates the contact sequence and the units digit indicates the function (1/2 for Normally Closed, 3/4 for Normally Open). For example, 13 and 14 represent the first set of Normally Open auxiliary contacts.

NEMA ICS 2 (North America Legacy)

NEMA schematics traditionally use a circle (or sometimes a rectangle) for the coil. Instead of the IEC numeric logic, legacy NEMA drawings often rely on letter designations for auxiliary contacts (e.g., NO and NC, or a and b contacts). Main power terminals are almost exclusively labeled L1, L2, L3 (Line) and T1, T2, T3 (Load). Modern NEMA-rated contactors (like the Eaton XTCE or Allen-Bradley 100-C series) often blend NEMA physical sizing with IEC terminal numbering to accommodate global supply chains.

Old UK BS 3939 (Obsolete but present in legacy plants)

If you are troubleshooting a panel in an older British Commonwealth facility, you may encounter the BS 3939 standard. The coil is represented by a circle with a diagonal cross inside it. Contacts are drawn with specific mechanical linkage lines. While superseded by IEC 60617 in the UK since the late 1980s, maintenance electricians still encounter these on original schematics for machinery built prior to 1990.

Rows and Markings People Get Wrong

Even experienced bench technicians and sparkies make assumptions that lead to blown fuses or dropped control logic. Here are the most common contactor symbol and terminal misinterpretations:

• Confusing Main and Auxiliary Ratings: A schematic might show a contact labeled "13-14" switching a 24VDC solenoid valve, while another shows "1-2" switching a 400VAC motor. The physical 13-14 auxiliary contacts on a standard TeSys D-line contactor are rated for roughly 10A at 600V, but they are not designed to break high inductive motor starting currents. Never use aux contacts for main power routing.
• Assuming Coil Polarity Doesn't Matter: If you are wiring an AC coil (e.g., 120VAC or 24VAC), polarity is irrelevant; A1 and A2 are interchangeable. However, if you are using a DC coil (e.g., 24VDC) with a built-in flyback diode or surge suppressor module, A1 must be positive and A2 must be negative. Reversing DC polarity on a diode-equipped coil will create a dead short, instantly blowing the control circuit fuse.
• The "14/13" vs "13/14" Directionality Myth: The IEC standard dictates that the lower number (13) is the input and the higher number (14) is the output. In practice, for a dry, potential-free auxiliary contact, current can flow in either direction. Do not waste time rewiring a control circuit just because the physical wire landed on 14 instead of 13, provided the schematic logic is maintained.
• Misreading the Tens Digit: If a contactor has multiple aux blocks, the tens digit changes (13-14, 43-44, 83-84). The units digit (3 and 4) always means Normally Open. If you see a 3 and a 4, it is NO, regardless of the first digit.

Safe Interpretation When Markings Are Faded or Missing

In harsh industrial environments—especially near CNC coolant, mining dust, or high-heat ovens—the printed terminal markings on a contactor chassis will fade or burn off. When you face an unmarked contactor and no schematic, you must safely map the terminals using a digital multimeter (DMM).

Step 1: Locate the Coil (A1/A2)
Set your DMM to the Ohms (Ω) setting. Probe pairs of smaller terminals. The coil will show a specific resistance. A 24VDC coil typically reads between 15Ω and 50Ω. A 120VAC coil will read much higher, often between 100Ω and 300Ω. If you read 0.0Ω (short) or OL (open), the coil is burned out and the contactor must be replaced. Terminals showing resistance are your A1 and A2.

Step 2: Map the Main Power Contacts (L/T)
Identify the three largest terminal pairs. With the contactor de-energized, place your probes across the top and bottom of each pair. They should read OL (open). Using a non-conductive tool (like a plastic spudger or an insulated screwdriver), firmly press down on the contactor's armature plunger. The meter should drop to < 0.5Ω, confirming these are the main Normally Open power contacts.

Step 3: Identify Auxiliary NO and NC
Probe the smaller side-mounted or front-mounted terminal pairs. - If the pair reads < 0.5Ω at rest, and goes OL when you press the plunger, you have found a Normally Closed (NC) set (IEC 21-22). - If the pair reads OL at rest, and drops to < 0.5Ω when you press the plunger, you have found a Normally Open (NO) set (IEC 13-14).
Label them immediately with a fine-tip permanent marker or adhesive terminal tape.

Frequently Asked Questions