3-Pole Contactor Symbol

The 3-Pole Contactor schematic symbol. Standard-specific details are listed below where available.

Definition: The 3-Pole Contactor symbol represents a heavy-duty electromechanical switching device with three main power contacts (L1, L2, L3 → T1, T2, T3) operated by an electromagnetic coil, used in schematics to denote a device that makes or breaks three-phase AC power circuits under load, as defined in IEC 60947-4-1 (low-voltage contactors for motor applications) and ANSI/NEMA ICS 2.

Also known as: three-pole contactor, 3-pole motor contactor, AC contactor, magnetic contactor, KM symbol, motor starter contactor.

What the 3-Pole Contactor symbol means

The 3-pole contactor symbol denotes an electromagnetically-operated switch with three sets of main (power) contacts rated to carry and interrupt the full load current of a three-phase circuit. When the operating coil is energised, the armature closes all three main contacts simultaneously, completing the three-phase circuit to the load. When the coil is de-energised, a return spring opens all contacts, disconnecting the load.

In motor-control schematics the 3-pole contactor is the primary switching device for three-phase induction motors. It appears in Direct-On-Line (DOL) starters, star-delta starters, reversing starters, and Variable Frequency Drive bypass circuits. The reference designator for a contactor is KM (per IEC 60617) or M (NEMA convention). A complete contactor assembly also includes auxiliary contacts (NC and NO) drawn separately and a coil symbol.

How to identify the 3-Pole Contactor symbol

The 3-pole contactor symbol is drawn as three pairs of switching contacts arranged vertically or side by side, one pair for each phase (L1/T1, L2/T2, L3/T3). Each contact pair is shown as two horizontal bars with a bridging movable contact bar — the IEC convention uses a diagonal bridge across an open gap to indicate a normally-open main contact. The three contact pairs are grouped together by a dashed box or linked by a mechanical coupling line indicating that they operate simultaneously from a single coil. Incoming terminals are labelled L1, L2, L3 (line side) and outgoing terminals T1, T2, T3 (load side).

Function and usage boundary

The 3-pole contactor connects or disconnects a three-phase load (typically an induction motor) from the supply voltage in response to a control signal applied to the coil. When the coil voltage (A1–A2) is applied, the electromagnetic force pulls in the armature, closing all three main contacts at once. The contacts are designed with silver-alloy tips and an arc-quenching chamber so they can safely interrupt the inrush current of a motor start or the running current of up to several hundred amperes. The device is rated for high endurance (millions of operating cycles), unlike a circuit breaker, because it is intended for frequent operation as part of motor-control logic.

Standards: IEC vs ANSI

IEC 60617	IEC 60947-4-1 (Low-voltage switchgear — Part 4-1: Contactors and motor-starters) defines contactor ratings, utilisation categories (AC-1 through AC-4), and the schematic symbol. IEC 60617-07 specifies the switching element symbol with three mechanically-linked contacts and the coil symbol as a rectangle.
ANSI/IEEE 315	ANSI/NEMA ICS 2 and NEMA ICS 6 define contactor ratings and symbols for North American motor control. IEEE 315-1975 / ANSI Y32.2 specifies the contact symbols. NEMA contactors are rated in 'sizes' (Size 00 through Size 9) while IEC contactors are rated in amperes.
Key difference	IEC contactors use an ampere-based rating with utilisation categories (AC-3 for squirrel-cage motors, AC-4 for plugging/inching); NEMA contactors use a size-based rating. The schematic symbols are functionally identical — both show three normally-open main contacts with a mechanical linkage — but IEC drawings use the IEC 60617 bridge-contact style while NEMA drawings may use a simpler line-and-dot convention.

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Logical terminals

Logical ID	Editor terminal name
l1	L1
l2	L2
l3	L3
t1	T1
t2	T2
t3	T3

Where the 3-Pole Contactor symbol is used

Direct-On-Line (DOL) motor starters — a single KM contactor connects a three-phase induction motor directly to the supply, operated by start/stop push buttons through overload relay contacts.
Star-delta starters — two or three contactors (main KM, star KY, delta KD) work in sequence to reduce motor starting current by initially connecting the motor in star configuration then switching to delta.
Reversing starters — two 3-pole contactors wired with interlocks reverse two supply phases (L1/L3 swapped) to reverse motor direction; only one contactor may be closed at a time.
Capacitor bank switching — 3-pole contactors switch power-factor-correction capacitor banks on and off in response to reactive power demand, with AC-6b utilisation category rating for capacitive loads.
HVAC compressor control — large air-conditioning compressors (5 kW to 100 kW) are switched by 3-pole contactors controlled by thermostats or building management systems.
Pump and conveyor motor control — industrial water pumps, conveyor belts, and fan motors use 3-pole contactors in combination with thermal overload relays to provide protected motor switching and overload protection.

Key facts

The 3-pole contactor symbol shows three mechanically-linked normally-open main contacts with line-side terminals L1, L2, L3 and load-side terminals T1, T2, T3, operated by a separate electromagnetic coil (A1–A2).
The IEC reference designator for a contactor is KM; in North American NEMA drawings the designator M (for magnetic motor starter) is commonly used.
IEC 60947-4-1 defines utilisation categories for contactors: AC-3 (switching squirrel-cage motors during run) is the most common, while AC-4 (plugging and inching) requires a higher-rated contactor for the same motor.
A contactor is NOT a protective device — it cannot interrupt fault currents. It must always be used with a circuit breaker or fuse for short-circuit protection and a thermal overload relay for motor overload protection.
Contactor coil voltages are independent of the main circuit voltage; a 230 V coil contactor can switch a 400 V three-phase circuit, and a 24 V DC coil contactor is common in PLC-controlled systems.
Mechanical and electrical endurance ratings distinguish contactors from switches: a typical IEC contactor is rated for 10 million mechanical operations and 1 million electrical operations at rated current.
Pins on this symbol: L1 (x=10 y=0), L2 (x=25 y=0), L3 (x=40 y=0) on the line side; T1 (x=10 y=60), T2 (x=25 y=60), T3 (x=40 y=60) on the load side.
Auxiliary contacts (NO and NO) are drawn separately from the main contacts in IEC wiring diagrams; they share the same coil and mechanical linkage but are used for control-circuit interlocking and status indication.

Frequently asked questions

What does the 3-pole contactor symbol look like?

The 3-pole contactor symbol shows three sets of normally-open main contacts arranged in parallel (one per phase), with the line-side terminals labelled L1, L2, L3 at the top and load-side terminals T1, T2, T3 at the bottom. A dashed box or mechanical linkage line connects all three contact symbols to indicate they operate simultaneously. The coil symbol (a rectangle labelled A1–A2) is drawn separately.

What is the difference between a contactor and a circuit breaker?

A contactor is designed for frequent switching (millions of cycles) under normal load current but cannot interrupt fault or short-circuit currents. A circuit breaker is designed to interrupt fault currents but is not rated for frequent switching. In a motor-control circuit both devices are used together: the circuit breaker provides short-circuit protection, and the contactor provides the frequent start/stop switching.

What do L1, L2, L3, T1, T2, T3 mean on a contactor?

L1, L2, L3 are the Line-side terminals where the three-phase supply is connected. T1, T2, T3 are the Load-side (or Transformer-side) terminals connected to the motor or other load. When the contactor closes, L1 connects to T1, L2 to T2, and L3 to T3, completing the three-phase circuit.

What is the IEC standard for 3-pole contactors?

IEC 60947-4-1 (Low-voltage switchgear and controlgear — Part 4-1: Contactors and motor-starters) is the primary standard defining contactor ratings, utilisation categories, and test requirements. IEC 60617-07 defines the schematic symbols. The NEMA equivalent is ANSI/NEMA ICS 2 for North American contactors.

What is the reference designator for a contactor on a schematic?

The IEC reference designator for a contactor is KM (K for contactor, M for main). NEMA drawings often use M alone. Multiple contactors in the same panel are numbered KM1, KM2, etc. The coil and all auxiliary contacts associated with one contactor share the same KM number throughout the drawing.

What is the AC-3 utilisation category for a contactor?

AC-3 is the IEC 60947-4-1 utilisation category for making and breaking the stall current of a squirrel-cage induction motor during normal starting and stopping. Under AC-3, the contactor must close against motor inrush current (typically 6–8 times full-load current) and open the running current. AC-4 (plugging, inching) requires the contactor to make and break both inrush and running current in rapid succession and needs a higher-rated device.

Can a contactor work without an overload relay?

A contactor can operate without an overload relay, but doing so provides no motor overload protection. If the motor stalls or is overloaded, it will overheat and burn out. Best practice per IEC 60947-4-1 and NEC Article 430 is to always combine the contactor with a thermal or electronic overload relay sized to the motor's full-load current to provide Class 10 or Class 20 trip protection.

Related symbols

Physical components that use this symbol

A schematic symbol defines electrical intent; the physical profile adds package or panel dimensions and mounting data.

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