Contactor NO Contact Symbol
Definition: The Contactor NO Contact symbol represents a normally-open (NO) auxiliary contact of a contactor, drawn as two terminal bars with an open gap and a diagonal bridging line showing the open default state, used in control-circuit wiring diagrams to denote a contact that is open when the contactor coil is de-energised and closes when the coil is energised, as specified under IEC 60617-07 and ANSI/IEEE 315.
Also known as: normally open contact, NO auxiliary contact, contactor NO contact, make contact, a-contact, seal-in contact, hold contact.
What the Contactor NO Contact symbol means
The contactor NO contact symbol represents an auxiliary contact that is physically open (non-conducting) in the rest state of the contactor — when the coil is not energised — and closes (becomes conducting) when the coil is energised and the armature moves. This contact is known as a 'make contact' or 'a-contact' in IEC 60617 terminology, and 'normally open' (NO) in NEMA/IEEE convention.
NO contacts are used in motor-control circuits primarily as seal-in (hold-in, self-latching) contacts, where one NO contact of the contactor is wired in parallel with the start push button. When the contactor picks up, this NO contact closes, holding the coil energised after the momentary start button is released. NO contacts are also used to start downstream sequences (the NO contact of motor 1 in series with the coil of motor 2 ensures motor 2 cannot start until motor 1 is running), and as running-status feedback inputs to PLCs.
How to identify the Contactor NO Contact symbol
In IEC 60617-07 the normally-open contact symbol consists of two short horizontal bars (fixed contacts) separated by a gap, with a diagonal bridging line that does not cross the gap — indicating the open state. The two terminal connections enter and exit vertically above and below. In ANSI/IEEE 315 the NO contact is drawn as two parallel short horizontal lines with a clear open space between them, and a diagonal line angled above the gap to indicate the movable contact bridge that will close the gap when actuated. The symbol is labelled with the parent contactor designator, such as KM1 NO.
Function in a circuit
The NO auxiliary contact provides a low-current control-circuit switching element that closes when the contactor energises. When the coil is de-energised, the contact spring holds the bridge away from one fixed contact, keeping the circuit open. When the coil energises, the armature movement forces the bridge to make contact with both pads, closing the control circuit. The NO contact is rated for auxiliary, not power, duties — typically 6 A–10 A at 230 V AC (AC-15 per IEC 60947-5-1). Common uses include sealing-in the contactor coil, proving the contactor state to a PLC, initiating timing sequences, and driving pilot indicators.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-07 defines the normally-open (make contact) symbol as the 'a-contact' with an open gap between the contact bars. IEC 60947-5-1 specifies auxiliary contact ratings: AC-15 (inductive AC load), DC-13 (inductive DC load), voltage ranges, and electrical endurance requirements. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315-1975 depicts the NO contact as two parallel lines with an open gap and an angled bridge above the gap. NEMA ICS 2 specifies NO contact ratings in NEMA size categories consistent with IEC AC-15 ratings. |
| Key difference | The IEC and ANSI symbols convey the same meaning but differ graphically: IEC shows a clean open-gap bridge symbol; ANSI shows a diagonal movable-contact line angled to the opening. Both are read as 'open at rest, closes when operated'. Both standards use the same terminal labelling (In/Out or numbered terminals). |
Terminals / pins
| Pin | Name |
|---|---|
| in | In |
| out | Out |
Typical values
Rated current: 6 A–10 A AC-15 (IEC 60947-5-1, 230 V AC inductive). DC rating: 6 A DC-13 (24 V DC inductive). Maximum voltage: up to 690 V AC / 250 V DC. Minimum current (gold-plated contacts): 1 mA at 24 V. Contact resistance: < 50 mΩ. Electrical endurance: 1–3 million operations at rated load. Mechanical endurance: 10–30 million operations.
Where the Contactor NO Contact symbol is used
- Seal-in (self-latching) contact — one NO contact of contactor KM1 is wired in parallel with the momentary start push button so that when KM1 picks up the NO contact seals in, keeping the coil energised after the start button is released.
- PLC running-status feedback — KM1 NO contact wired to a PLC digital input signals that the contactor is closed and the motor is running, enabling the PLC to confirm the motor started and detect a failed contactor (output energised but NO feedback remains open).
- Sequential motor starting — the NO contact of motor 1's contactor (KM1 NO) in series with the coil circuit of motor 2's contactor ensures motor 2 cannot start until motor 1 is confirmed running.
- Running indicator lamp — a NO contact powers a green 'running' pilot lamp when the contactor is closed, giving operators a visual confirmation that the motor is energised.
- Timer circuit initiation — the NO contact of a main contactor in series with a time-delay relay coil starts the timing sequence at the moment the contactor closes, automating timed transitions in star-delta and soft-starter bypass circuits.
- Safety relay output monitoring — safety relay modules use NO contacts to enable contactor coils; when the safety relay is de-energised (emergency stop or guard open), all NO contacts open, de-energising all motor contactors in the safety zone.
Example
In the control circuit of a DOL motor starter, one NO contact of contactor KM1 (KM1 NO) is connected in parallel with the start push button (PB1 NO). When PB1 is pressed, KM1 coil energises, KM1 main contacts close (motor starts), and KM1 NO auxiliary contact closes. When PB1 is released, current continues to flow through the KM1 NO contact, maintaining the coil energised and the motor running. The circuit is held in this latched state until the stop button (NC) is pressed, interrupting the coil circuit and dropping out KM1.
Key facts
- The Contactor NO Contact symbol represents a contact that is OPEN in the normal (coil de-energised) state and CLOSES when the contactor coil is energised — the opposite behaviour from a NC contact.
- The IEC term for a normally-open contact is 'a-contact' (make contact); the NEMA/IEEE term is 'normally open' (NO). Both describe the same behaviour: open at rest, closes when actuated.
- The most critical use of a NO auxiliary contact in a motor-starter circuit is as the 'seal-in' or 'hold-in' contact: it latches the contactor coil energised after the momentary start push button is released.
- NO auxiliary contacts are rated for low-current control circuits — typically 6 A at AC-15 (IEC 60947-5-1) — and must not be used as main power contacts for motor loads.
- All NO contacts on a contactor close simultaneously when the coil energises, regardless of which auxiliary contact block they are physically located on — they all share the same armature mechanism.
- Pins on this symbol: In (x=10 y=0) — top terminal; Out (x=10 y=50) — bottom terminal. Circuit is open (non-conducting) when the contactor is at rest.
- Additional NO contact blocks can be added to most IEC contactors as plug-on or clip-on auxiliary contact modules when more feedback points or interlock contacts are needed than the base contactor provides.
- A welded NO contact (fused closed due to an inrush or fault event) means the contact fails to open when the coil de-energises, causing the load to remain powered and the PLC to receive a spurious 'running' feedback signal.
Diagrams that use this symbol
- relay diagram
- dol starter diagram
- relay wiring diagram
- relay connection diagram
- 4 pin relay wiring diagram
- diagram what wires go to the starter solenoid
- 5 pin relay wiring diagram
- 3 phase induction motor diagram
Frequently asked questions
What does the contactor NO contact symbol look like?
The NO contact symbol in IEC 60617-07 shows two short horizontal bars separated by an open gap, with a diagonal bridging line positioned above or beside the gap — indicating the contact bridge is not yet touching. In ANSI/IEEE 315 it is two parallel lines with a clear gap and a diagonal line showing the movable bridge. The symbol is labelled with the parent designator, for example KM1 NO.
What does NO mean on a contactor auxiliary contact?
NO means Normally Open: the contact is open (electrically non-conducting) when the contactor coil is de-energised (the rest or normal state). When the coil is energised and the armature moves, the NO contact closes and becomes conducting. When the coil is de-energised again, the contact returns to its open state.
What is the difference between NO and NC contacts on a contactor?
A Normally Open (NO) contact is open at rest and closes when the coil energises. A Normally Closed (NC) contact is closed at rest and opens when the coil energises. Energising the contactor coil closes all NO contacts and opens all NC contacts simultaneously. In a wiring diagram NO and NC contacts from the same contactor share the same KM designator but are labelled NO or NC respectively.
What is a seal-in contact and why is it needed?
A seal-in contact (also called a hold-in or self-holding contact) is a NO auxiliary contact wired in parallel with the momentary start push button. When the contactor picks up from the start button press, the seal-in NO contact closes, providing an alternative current path to keep the coil energised after the start button is released. Without a seal-in contact, the motor would only run while the start button is held pressed.
What is the current rating of a contactor NO auxiliary contact?
Standard IEC auxiliary contacts (NO and NC) are rated at 6 A to 10 A at AC-15 (230 V AC inductive load per IEC 60947-5-1). DC-13 (inductive DC) rating is typically 6 A at 24 V. 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 signals.
How do I tell a NO contact from a NC contact in a wiring diagram?
In an IEC wiring diagram, a NO contact has an open gap with no perpendicular bar across the bridge — visually showing the contact is not touching. A NC contact has a perpendicular marker crossing the diagonal line, showing the contact is 'held in'. In ANSI diagrams, the NO contact has a clear open space between the two parallel contact bars, while the NC contact has a diagonal slash across that space. The label NO or NC alongside the designator also confirms the type.
What standard defines the contactor NO contact symbol?
IEC 60617-07 (Switching devices) defines the normally-open contact ('a-contact') symbol for use in schematic and wiring diagrams. ANSI Y32.2 / IEEE 315-1975 defines the equivalent ANSI symbol. IEC 60947-5-1 specifies the electrical ratings, endurance requirements, and performance standards for the physical auxiliary contact blocks.
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