Contactor NC Contact Symbol

Q: What does the contactor NC contact symbol look like?

The NC contact symbol in IEC 60617-07 shows two short horizontal bars (the fixed contacts) with a diagonal bridging line and a perpendicular marker across it indicating the normally-closed state. In ANSI/IEEE 315 it is drawn as two parallel lines with a diagonal slash through the gap. The symbol is labelled with the parent contactor designator, for example KM1 NC.

Q: What does NC mean on a contactor contact?

NC means Normally Closed: the contact is closed (electrically conducting) when the contactor coil is de-energised (the rest or normal state). When the coil is energised and the armature moves, the NC contact opens and becomes non-conducting. If the coil is de-energised again, the contact returns to its closed state.

Q: What is the difference between NC and NO contacts on a contactor?

A Normally Closed (NC) contact is closed at rest and opens when the coil energises. A Normally Open (NO) contact is open at rest and closes when the coil energises. In a contactor, both NC and NO contacts operate simultaneously from the same coil; energising the coil opens all NC contacts and closes all NO contacts at the same moment.

Q: What are NC contacts used for in motor control circuits?

NC contacts are most commonly used for interlocking (preventing conflicting operations), feedback monitoring, and safety switching. In reversing motor starters, the NC contact of each direction contactor is wired in series with the opposite direction coil to prevent both contactors from energising simultaneously, which would cause a three-phase short circuit.

Q: What is the current rating of a contactor NC auxiliary contact?

Standard IEC auxiliary contacts are rated 6 A to 10 A at AC-15 (230 V AC inductive load, per IEC 60947-5-1) and 6 A at DC-13 (24 V DC inductive). They are not rated for high-current power loads. Gold-plated low-energy contacts used for PLC inputs are rated as low as 1 mA at 24 V to ensure reliable switching of milliampere-level sensor circuits.

Q: What standard defines the contactor NC contact symbol?

IEC 60617-07 (Switching devices and protective devices) defines the normally-closed contact symbol for use in schematic and wiring diagrams. ANSI Y32.2 / IEEE 315-1975 defines the equivalent symbol for North American drawings. IEC 60947-5-1 specifies the electrical ratings and performance requirements for the physical auxiliary contacts.

Q: How do I tell if a contactor contact is NC or NO from a wiring diagram?

In an IEC wiring diagram, a NC contact is identified by the perpendicular bar crossing the diagonal bridging line on the contact symbol — visually suggesting the contact bridge is 'held in' across the gap. A NO contact has no such bar, showing the bridge is open. In ANSI diagrams, the diagonal slash through the gap for NC vs the open gap for NO provides the same distinction. The designator label (KM1 NC or KM1 NO) also confirms the contact type.

The Contactor NC Contact schematic symbol. Standard-specific details are listed below where available.

Definition: The Contactor NC Contact symbol represents a normally-closed (NC) auxiliary contact of a contactor, drawn as two terminal bars with a diagonal bridging line and a perpendicular stroke indicating the closed default state, used in control-circuit wiring diagrams to denote a contact that is closed when the contactor coil is de-energised and opens when the coil is energised, as specified under IEC 60617-07 and ANSI/IEEE 315.

Also known as: normally closed contact, NC auxiliary contact, contactor NC contact, closed contact symbol, break contact, b-contact.

What the Contactor NC Contact symbol means

The contactor NC contact symbol represents one auxiliary contact element that is physically closed (conducting) in the rest (de-energised) state of the contactor and opens (becomes non-conducting) when the coil is energised and the armature moves. In relay and contactor terminology this contact is also called a 'break contact' or 'b-contact' in IEC standards, or a 'normally closed' contact in NEMA/IEEE convention.

NC contacts are essential for control-circuit interlocking, safety monitoring, and feedback signalling. They appear in motor-control circuits to prevent conflicting operations — for example, the NC contact of a forward contactor inserted in series with the reverse contactor coil prevents both directions from being energised simultaneously. They are also used to provide a 'running' indicator signal (the NC contact opens when the motor starts) or to de-energise a downstream device when the main contactor picks up.

How to identify the Contactor NC Contact symbol

The IEC 60617-07 normally-closed contact symbol consists of two short horizontal bars (the fixed and movable contact elements) connected by a diagonal or angled bridging line, with a short perpendicular bar or slash crossing the bridging line to indicate the normally-closed (closed at rest) state. The two terminal connections enter and exit vertically above and below the contact symbol. In ANSI/IEEE 315 the NC contact is drawn as two parallel horizontal lines with a diagonal slash through the gap — a common-sense shorthand for 'the gap is closed'. The symbol is labelled with the parent contactor's designator plus 'NC', for example KM1 NC.

Function and usage boundary

The NC auxiliary contact provides a low-current (typically < 10 A) control-circuit switching element that mirrors the contactor's mechanical state. When the coil is de-energised (contactor open), the NC contact spring-holds the contact bridge against both contact pads, completing the control circuit through the contact. When the coil energises and the armature moves, the NC contact opens, breaking the control circuit. The contact reverts to closed when the coil de-energises. NC contacts are not rated for power-circuit loads; they handle only the milliampere to low-ampere currents of control circuits, PLC inputs, indicator lamps, and safety relay coils.

Standards: IEC vs ANSI

IEC 60617	IEC 60617-07 defines the NC contact symbol as the 'normally-closed switching function' with the closed-state indicator (perpendicular bar across the contact gap). IEC 60947-5-1 covers auxiliary contact blocks for contactors, specifying rated current (typically 10 A AC-15 or DC-13), voltage, and endurance.
ANSI/IEEE 315	ANSI Y32.2 / IEEE 315-1975 depicts the NC contact as two parallel lines with a diagonal line through the contact gap. NEMA ICS 2 specifies NC contact ratings consistent with IEC auxiliary contact standards.
Key difference	IEC and ANSI symbols convey the same meaning but use slightly different graphical conventions. The IEC symbol uses a diagonal bridge with a perpendicular 'closed' marker; the ANSI symbol uses two parallel short lines with an oblique slash. Both unambiguously indicate a contact that is closed when the operating device is in its normal (de-energised) state.

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Logical terminals

Logical ID	Editor terminal name
in	In
out	Out

Where the Contactor NC Contact symbol is used

Motor direction interlocking — the NC contact of a forward contactor (KM1 NC) is wired in series with the reverse contactor coil (KM2), and the NC contact of KM2 is in series with KM1 coil, creating a hard-wired interlock that prevents simultaneous energisation of both contactors.
Control-circuit feedback to PLC — the KM NC contact wired to a PLC digital input signals the processor that the contactor is currently de-energised (motor not running), enabling the PLC to detect welded contacts or failure to open.
Star-delta transition monitoring — in a star-delta starter, the NC contact of the delta contactor (KD) in series with the star contactor coil (KY) ensures the star contactor cannot remain energised once the delta contactor picks up.
Safety relay monitoring — the NC contact of a safety relay in series with the motor contactor coil provides an automatic de-energisation path when the safety relay opens due to a light curtain, door interlock, or emergency stop actuation.
Indicator lamp circuits — an NC contact energises a 'stopped' or 'ready' indicator lamp when the contactor is open, providing visual confirmation that the motor is de-energised before maintenance access.
Sequencing in automation — in multi-motor systems, the NC contact of motor 1's contactor (KM1 NC) prevents motor 2 from starting until motor 1 is proven to be running (KM1 picks up, its NC contact opens, and a timer-controlled logic change permits motor 2's coil to energise).

Key facts

The Contactor NC Contact symbol represents a contact that is CLOSED in the normal (coil de-energised) state and OPENS when the contactor coil is energised; this is the opposite behaviour from a NO contact.
NC contacts are auxiliary low-current contacts (typically 6–10 A, AC-15 rated per IEC 60947-5-1), not main power contacts; they are used only in control circuits, indicator circuits, and PLC input circuits.
The IEC term for a normally-closed contact is 'b-contact' (break contact); the NEMA/IEEE term is 'normally closed' (NC). Both describe the same behaviour: closed at rest, open when actuated.
NC auxiliary contacts share the same mechanical linkage as the main power contacts and the contactor coil; when KM1 coil energises, ALL KM1 NO contacts close and ALL KM1 NC contacts open simultaneously.
Contact bounce (chatter) on NC contacts during armature movement can cause false signals in PLC inputs; this is mitigated by input filter times (typically 10–20 ms) configured in the PLC.
Pins on this symbol: In (x=10 y=0) — top terminal; Out (x=10 y=50) — bottom terminal. Current flows In → Out when the contact is closed (coil de-energised).
Standard auxiliary contact blocks can be added to most IEC contactors as plug-in or screw-on modules providing additional NC and NO contacts beyond the contacts built into the contactor body.
Welded contacts (a contact that has fused closed due to an overcurrent event) on an NC contact mean the contact fails to open when the coil energises — this is detected by a PLC as the NC feedback input remaining high after the coil signal is given.

Frequently asked questions

What does the contactor NC contact symbol look like?

The NC contact symbol in IEC 60617-07 shows two short horizontal bars (the fixed contacts) with a diagonal bridging line and a perpendicular marker across it indicating the normally-closed state. In ANSI/IEEE 315 it is drawn as two parallel lines with a diagonal slash through the gap. The symbol is labelled with the parent contactor designator, for example KM1 NC.

What does NC mean on a contactor contact?

NC means Normally Closed: the contact is closed (electrically conducting) when the contactor coil is de-energised (the rest or normal state). When the coil is energised and the armature moves, the NC contact opens and becomes non-conducting. If the coil is de-energised again, the contact returns to its closed state.

What is the difference between NC and NO contacts on a contactor?

A Normally Closed (NC) contact is closed at rest and opens when the coil energises. A Normally Open (NO) contact is open at rest and closes when the coil energises. In a contactor, both NC and NO contacts operate simultaneously from the same coil; energising the coil opens all NC contacts and closes all NO contacts at the same moment.

What are NC contacts used for in motor control circuits?

NC contacts are most commonly used for interlocking (preventing conflicting operations), feedback monitoring, and safety switching. In reversing motor starters, the NC contact of each direction contactor is wired in series with the opposite direction coil to prevent both contactors from energising simultaneously, which would cause a three-phase short circuit.

What is the current rating of a contactor NC auxiliary contact?

Standard IEC auxiliary contacts are rated 6 A to 10 A at AC-15 (230 V AC inductive load, per IEC 60947-5-1) and 6 A at DC-13 (24 V DC inductive). They are not rated for high-current power loads. Gold-plated low-energy contacts used for PLC inputs are rated as low as 1 mA at 24 V to ensure reliable switching of milliampere-level sensor circuits.

What standard defines the contactor NC contact symbol?

IEC 60617-07 (Switching devices and protective devices) defines the normally-closed contact symbol for use in schematic and wiring diagrams. ANSI Y32.2 / IEEE 315-1975 defines the equivalent symbol for North American drawings. IEC 60947-5-1 specifies the electrical ratings and performance requirements for the physical auxiliary contacts.

How do I tell if a contactor contact is NC or NO from a wiring diagram?

In an IEC wiring diagram, a NC contact is identified by the perpendicular bar crossing the diagonal bridging line on the contact symbol — visually suggesting the contact bridge is 'held in' across the gap. A NO contact has no such bar, showing the bridge is open. In ANSI diagrams, the diagonal slash through the gap for NC vs the open gap for NO provides the same distinction. The designator label (KM1 NC or KM1 NO) also confirms the contact type.

Related symbols

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