The schematic symbol for a contactor is not a single icon. It is a distributed composite of an electromagnetic coil symbol and multiple switch contact symbols (main power and auxiliary control) linked by a mechanical dashed line or alphanumeric designation. Because a contactor physically separates high-amperage motor loads from low-voltage logic circuits, reading its schematic requires understanding both the power path and the control path. Below is the complete reference data you need to interpret these symbols on the bench or in the field.
Complete Contactor Schematic Symbol Reference Table
This table maps the physical components of a standard 3-pole industrial contactor to their schematic representations and terminal markings. Use this as your primary field reference when tracing ladder logic or IEC functional diagrams.
| Component | IEC 60617 Symbol Shape | NEMA / ANSI Symbol Shape | Standard Terminal Markings (IEC) | Practical Application & Ratings |
|---|---|---|---|---|
| Contactor Coil | Circle or rectangle with diagonal lines; labeled A1/A2 or KM1 | Circle labeled with ladder line numbers or device ID (e.g., 1M) | A1 (Positive/Line), A2 (Negative/Neutral) | Actuates the armature. Typical voltages: 24VDC, 120VAC, 240VAC, 480VAC. Draws 20VA to 100VA inrush. |
| Main Power Contacts (NO) | 3-pole NO switch symbol, mechanically linked. Marked 1L1/2T1, 3L2/4T2, 5L3/6T3 | 3-pole NO switch symbol. Marked L1/T1, L2/T2, L3/T3 | 1L1, 3L2, 5L3 (Line) 2T1, 4T2, 6T3 (Load) |
Switches the primary motor or heater load. Handles 9A to 800A+. Equipped with arc chutes. |
| Auxiliary NO Contact | Single NO switch symbol. Marked with a two-digit code ending in 4 | Single NO switch symbol, labeled with device ID (e.g., 1M-1) | 13 (Line), 14 (Load) | Used for PLC inputs, seal-in circuits, or indicator lights. Typically rated for 1A to 5A at 120VAC. |
| Auxiliary NC Contact | Single NC switch symbol. Marked with a two-digit code ending in 2 | Single NC switch symbol, labeled with device ID | 21 (Line), 22 (Load) | Used for electrical interlocks, fault indication, or safety relay feedback loops. Rated 1A to 5A. |
| Mechanical Interlock | Dashed mechanical line linking two adjacent coil symbols | Dashed line linking coils, often labeled 'MI' | N/A (Mechanical linkage, no electrical terminals) | Prevents two reversing contactors from closing simultaneously. Critical for forward/reverse motor control. |
Regional Standards: IEC vs. NEMA Symbol Variants
How a contactor is drawn and labeled depends entirely on the regional standard governing the schematic. Misinterpreting a NEMA ladder diagram as an IEC functional diagram will lead to severe wiring errors.
The IEC 60617 Approach (Global / Europe)
IEC schematics focus on terminal-level physical wiring. The standard relies heavily on a two-digit numbering system for auxiliary contacts. The first digit indicates the sequence or position of the contact on the contactor (1, 2, 3...). The second digit indicates the function:
- 1-2: Normally Closed (NC)
- 3-4: Normally Open (NO)
- 5-6: NC with time delay (late break / early make)
- 7-8: NO with time delay (late make / early break)
Therefore, if you see terminals 13 and 14 on a Schneider TeSys D contactor, you immediately know it is the first auxiliary contact (1), and it is Normally Open (3-4). If you see 21 and 22, it is the second auxiliary contact (2), Normally Closed (1-2).
The NEMA ICS 1 Approach (North America)
NEMA ladder logic abstracts the physical terminals in favor of logical flow. Contacts are rarely labeled with physical terminal numbers like 13/14. Instead, they are labeled with the device designation (e.g., 1M for Motor Starter 1) and placed on ladder rungs referenced by line numbers. To wire a NEMA schematic, you must cross-reference the logical line number with the manufacturer's physical wiring diagram to find which physical screw terminal corresponds to '1M-1'.
The 'Rows People Get Wrong' & Faded Label Troubleshooting
Even experienced technicians make specific errors when interpreting contactor schematics and mapping them to physical hardware. Here are the most common pitfalls and how to resolve them when the physical contactor label is degraded.
Mistake 1: Confusing Main Power NO with Auxiliary NO
On a schematic, a main power NO contact and an auxiliary NO contact look nearly identical—both are drawn as a standard NO switch symbol. The difference is the terminal designation and the physical hardware. Main contacts (L1/T1) are designed to break heavy inductive motor loads and feature internal arc chutes. Auxiliary contacts (13/14) are simple logic switches. Wiring a 15A motor load through a 13/14 auxiliary block will instantly melt the block and create an arc flash hazard. Always verify the terminal prefix (L/T vs. numeric) on the schematic.
Mistake 2: Assuming the Coil Symbol Dictates Voltage
The schematic symbol for a contactor coil tells you that it is a coil, but it does not tell you the required voltage. A coil drawn on a 480VAC 3-phase schematic might actually be a 120VAC coil fed by a step-down control transformer. Always check the physical coil label or the schematic's bill of materials (BOM) before applying control power.
Industrial environments destroy printed labels. If the wiring diagram on the cover of an Eaton XTCE or Square D contactor is rubbed off or missing, never guess the terminal functions. Miswiring a 480V main phase into a 24VDC PLC input will destroy the PLC and pose a lethal shock hazard.
The Multimeter Verification Protocol:
- De-energize and Lockout/Tagout (LOTO) the panel. Verify dead with a tested CAT III/IV meter.
- Find the Coil: Set your DMM to resistance (Ohms). Probe pairs of small terminals (usually A1/A2). A healthy 120VAC coil will read between 15Ω and 50Ω. A 24VDC coil will read much lower (typically 2Ω to 10Ω). An open reading (OL) means a blown coil.
- Map the Auxiliaries: Set the DMM to continuity. With the contactor de-energized, probe the smaller side-mount or front-mount terminals. Terminals that beep are your NC contacts (e.g., 21/22). Terminals that read OL are your NO contacts (e.g., 13/14). Manually press the armature down with a non-conductive tool; the continuity states should swap.
Mapping Schematics to Physical Hardware (TeSys & XTCE Examples)
To bridge the gap between the schematic symbol and the physical lugs, let us look at how modern manufacturers implement these standards on their most popular platforms.
Schneider Electric TeSys D (LC1D Series):
The LC1D series strictly follows IEC 60617. The main power lugs are clearly marked 1L1, 3L2, 5L3 on the top and 2T1, 4T2, 6T3 on the bottom. The coil is universally A1 and A2. However, the auxiliary contacts are often modular. If you need more NO/NC contacts than the base unit provides, you clip on a front-mount auxiliary block (like the LADN11 or LADN22). The schematic symbol for these added blocks remains identical to the base aux contacts, but physically, they add new terminal sets (e.g., adding 33/34 and 43/44) to the physical device.
Eaton XTCE Series:
Eaton's XTCE line bridges the gap between IEC physical sizing and NEMA market expectations. While the physical terminals use IEC numbering (L1/T1, A1/A2, 13/14), the documentation and schematics provided for North American markets often overlay NEMA-style ladder logic designations. When wiring an XTCE contactor for a reversing motor starter, pay close attention to the mechanical interlock symbol. On the schematic, it is a dashed line between KM1 and KM2. Physically, it is a plastic and metal blocking lever installed between the two contactors that physically prevents the second armature from pulling in if the first is already engaged. If you omit the physical interlock despite wiring the electrical interlock (using 21/22 NC contacts in the opposing coil circuits), a welded main contact can still result in a catastrophic phase-to-phase short circuit.
Mastering the schematic symbol for a contactor means looking past the simple switch icons and understanding the terminal numbering logic, the regional standard in use, and the physical limitations of the auxiliary versus main power paths. Always verify with a meter before terminating wires on unmarked industrial control gear.
