Relay NO Contact Symbol
Definition: The Relay NO Contact symbol represents a Normally Open (NO) relay or contactor contact — defined in IEC 60617-07 and ANSI Y32.2 / IEEE 315 — a two-terminal switching element (In, Out) that is open (non-conducting) when its controlling coil or actuator is de-energised, and closes (completes the circuit) when the coil is energised.
Also known as: NO contact, normally open contact, make contact, a-contact, Form A contact, NO auxiliary contact.
What the Relay NO Contact symbol means
The Relay NO Contact symbol denotes a contact pair that is mechanically held in the open (non-conducting) state by spring pressure when no coil current flows. No current passes between In and Out in the normal (off) state. When the associated relay or contactor coil is energised, the armature overcomes the spring and the NO contact closes, completing the circuit between In and Out.
In wiring and control schematics, the NO contact symbol is used for load activation circuits: the load remains off until a control signal energises the relay coil, then the contact closes to switch the load on. This is the most common relay contact configuration for activation functions such as motor starting, lamp control, and solenoid actuation.
How to identify the Relay NO Contact symbol
The Relay NO Contact symbol is drawn as two short horizontal or vertical lines representing the fixed and moving contact terminals, with an open gap between them and no connecting slash — the gap indicates the contact is open (non-conducting) in the normal de-energised state. The absence of a diagonal slash distinguishes the NO symbol from the NC contact symbol, which has a slash bridging the gap.
Function in a circuit
The NO contact functions as a normally-open switch in a relay or contactor assembly. In the de-energised (normal) state, the moving contact is held away from the fixed contact by spring pressure, leaving an open gap between In and Out. When the coil is energised, the armature closes the gap, completing continuity from In to Out and allowing current to flow through the load circuit. The contact returns to open when coil power is removed, disconnecting the load.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-07 (switching devices) defines the NO contact symbol as an open gap between two contact lines, with no bridging diagonal. IEC 60947-5-1 specifies auxiliary NO contacts for low-voltage control circuits. IEC 61810 covers elementary relays with NO contacts. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 Section 13 defines the NO contact (Form A) as an open gap between two contact lines, identical in appearance to the IEC representation. IEEE 315 terms it a 'make contact' or 'Form A contact'. |
| Key difference | IEC 60617 and ANSI Y32.2 / IEEE 315 use the same NO contact symbol — an open gap with no bridging element. The Form A (ANSI/IEEE) and NO (IEC) designations are equivalent. Both standards position the moving contact arm to show the open rest-state gap. |
Terminals / pins
| Pin | Name |
|---|---|
| in | In |
| out | Out |
Typical values
Contact ratings vary by relay/contactor type. Typical auxiliary NO contact (IEC 60947-5-1): 10 A at 240 V AC, 10 A at 24 V DC. Main contactor NO contact: up to 800 A at 690 V AC (large contactors). Operating time: typically 10–50 ms. Bounce time: 1–5 ms. Endurance: 1–10 million mechanical operations for relay-type contacts.
Where the Relay NO Contact symbol is used
- Motor starter circuits where the NO main contacts close to connect three-phase power to the motor when the contactor coil is energised
- Control panel lamp indication circuits where an NO contact closes to illuminate a 'running' indicator when a machine starts
- Solenoid valve actuation circuits where the NO contact closes to energise the solenoid and open the valve
- PLC output relay contacts in NO configuration connecting to the load that must activate on command
- Holding (seal-in) circuits where an NO contact in parallel with the start button latches the coil on after the button is released
- Alarm circuits triggering on abnormal conditions — the alarm relay NO contact closes to energise a horn or indicator
Example
In a direct-on-line (DOL) motor starter circuit, the main contactor K1 has three NO main contacts that close simultaneously when K1 is energised, connecting the three-phase supply to the motor terminals; a fourth NO auxiliary contact of K1 in parallel with the Start button forms the seal-in (hold-on) circuit that keeps K1 energised after the Start button is released.
Key facts
- The Relay NO Contact has two pins: In and Out; current flows from In to Out only when the relay coil is energised and the contact has closed.
- An NO contact is open (non-conducting) when the relay coil is de-energised, and closes (conducting) when the coil is energised — the opposite of a Normally Closed (NC) contact.
- IEC 60617-07 and ANSI Y32.2 / IEEE 315 both represent the NO contact as an open gap between two contact lines with no bridging slash — the gap itself indicates the normal open state.
- NO contacts are designated Form A in ANSI/IEEE contact form terminology; NC contacts are Form B; changeover (SPDT) contacts are Form C.
- In self-holding (seal-in) circuits, an NO auxiliary contact in parallel with the start push-button maintains coil energisation after the button is released, a fundamental control circuit building block.
- NO contacts experience less electrical wear in applications where the load is off most of the time — the contact is open at rest and only carries current briefly during the energised period.
- The relay coil designator is K (e.g. K1); the associated NO contact is labelled K1-NO or shows the K1 reference against the NO contact symbol on the schematic.
Frequently asked questions
What does the relay NO contact symbol mean in a schematic?
The Relay NO (Normally Open) Contact symbol represents a contact that is open (non-conducting) when the relay coil is off and closes (conducting) when the coil is energised. It is drawn as an open gap between two contact lines with no bridging element, indicating the circuit is interrupted in the normal de-energised state.
What does the NO contact symbol look like?
The NO contact symbol shows two short lines (representing fixed and moving contact terminals) with an open gap between them and no diagonal slash. The absence of any bridging line across the gap indicates the contact is open (non-conducting) in the normal (coil-off) state. This distinguishes it from the NC symbol, which has a diagonal slash bridging the gap.
What is the difference between NO and NC relay contacts?
An NO (Normally Open) contact is open when the coil is off and closes when the coil is energised — used to activate a load. An NC (Normally Closed) contact is closed when the coil is off and opens when the coil is energised — used for fail-safe and interlock circuits. Both are defined in IEC 60617-07 and ANSI Y32.2 / IEEE 315.
What is a Form A contact?
Form A is the ANSI/IEEE designation for a Normally Open (NO) contact — a single-pole contact that is open in the de-energised (normal) state and closes when the coil is energised. Form B is Normally Closed (NC); Form C is SPDT (changeover with both NO and NC positions referenced to COM).
What standard defines the NO relay contact symbol?
IEC 60617-07 (switching devices) and ANSI Y32.2 / IEEE 315 Section 13 both define the NO contact symbol as an open gap between two contact lines with no bridging element. The two standards use essentially the same graphical symbol. Electrical performance of NO contacts is specified in IEC 61810 (relays) and IEC 60947-5-1 (auxiliary contacts).
What is a seal-in contact in relay control?
A seal-in (hold-on) contact is an NO auxiliary contact wired in parallel with the start push-button; when the button is pressed and the coil energises, the NO contact closes, providing an alternative current path that keeps the coil energised after the push-button is released. This is a standard DOL motor starter circuit technique.
How many terminals does an NO relay contact have?
An NO relay contact has two terminals — In and Out — which are open-circuit in the normal state and become connected when the relay coil energises. A full SPDT changeover contact has three terminals: COM, NO, and NC, where COM transfers from the NC position to the NO position on coil energisation.
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