Overload Contact NC Symbol
Definition: The Overload Contact NC symbol represents a normally-closed (NC) auxiliary contact of a thermal or electronic overload relay — standardised in IEC 60617-07 and ANSI Y32.2/IEEE 315 — which is closed under normal (non-tripped) conditions and opens when the overload relay trips due to excess motor current, with terminal designations In (pin 95) and Out (pin 96) per IEC 60947-4-1.
Also known as: overload NC contact, OL NC, normally closed overload contact, thermal overload NC, overload relay trip contact, 95-96 contact.
What the Overload Contact NC symbol means
The Overload Contact NC (normally closed) symbol represents the auxiliary trip contact of an overload relay that is closed during normal motor operation and opens when the overload relay detects an overcurrent condition (motor overload). In a motor starter control circuit, this NC contact is wired in series with the contactor coil control circuit: when the overload relay trips, the NC contact opens, de-energising the contactor coil and disconnecting the motor from the supply.
In IEC industrial control circuit diagrams, the overload NC contact is identified by terminal numbers 95 (In) and 96 (Out) per IEC 60947-4-1. In the de-energised (normal) state, the contact is closed; the motor runs normally. When a thermal or electronic overload relay detects sustained overcurrent, the bimetallic or electronic trip mechanism causes the NC contact to open, interrupting the control circuit and stopping the motor. The contact remains open until manually or automatically reset.
How to identify the Overload Contact NC symbol
The Overload Contact NC symbol is drawn as two horizontal parallel lines (representing the contact blades) with a diagonal slash or trip indicator line crossing through the contact gap, or as a standard NC contact symbol (two lines with a bar indicating the closed state) with an additional thermal trip indicator — commonly a small rectangle or 'OL' label above the symbol. In IEC 60617 notation, the symbol shows a normally-closed contact with a trip actuator indicator. ANSI schematics use a similar representation with a break contact symbol plus an overload designator.
Function in a circuit
The overload NC contact provides the protective trip function in motor starter control circuits. Under normal conditions, the contact is closed (conducting), keeping the contactor coil circuit energised and the motor running. When the overload relay detects a current exceeding the relay's set point for longer than the relay's trip time characteristic, the internal mechanism opens the NC contact, de-energising the contactor coil, which then opens the main contactor power contacts and stops the motor. This protects the motor windings from thermal damage due to sustained overcurrent, locked rotor, or phase loss.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-07 defines the normally-closed contact symbol used for overload relay contacts. IEC 60947-4-1 specifies overload relay requirements and assigns terminal numbers 95 (NC contact input) and 96 (NC contact output) for the trip contact. The IEC symbol for the NC overload contact includes the break-contact symbol with a trip actuator qualifier. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 uses a normally-closed contact symbol (horizontal lines with a bar) combined with a thermal element indicator for the overload relay NC contact. NEMA ICS standards govern motor starter overload relay performance in North American practice. |
| Key difference | IEC 60617-07 and ANSI Y32.2/IEEE 315 overload NC contact symbols differ in detail: IEC shows a break-contact with a specific thermal or electronic trip actuator marker; ANSI uses a break-contact symbol with a separate overload coil symbol or 'OL' annotation. Both indicate the same function — a contact that opens on overload trip. |
Terminals / pins
| Pin | Name |
|---|---|
| in | In |
| out | Out |
Typical values
Contact rating: typically 6 A AC-15 or 10 A AC-1 at 230/400 V AC (IEC 60947-5-1). Terminal numbers: 95 (In) and 96 (Out) per IEC 60947-4-1. Trip current range: adjustable, typically 0.1 A to 100 A depending on overload relay model. Reset: manual or automatic (selectable). Trip class: Class 10, 10A, 20, or 30 per IEC 60947-4-1.
Where the Overload Contact NC symbol is used
- DOL (Direct-On-Line) motor starter control circuit: NC contact in series with contactor coil, stops motor on overload trip
- Star-delta starter: overload NC contact monitors motor current during run condition, trips contactor coil if overloaded
- Conveyor belt drives: overload NC contact protects conveyor motor from jam-induced locked-rotor overload
- Pump control panels: overload NC contact stops pump on motor overload to prevent winding damage
- HVAC compressor control: overload relay NC contact in compressor contactor circuit provides thermal protection
- PLC-controlled motor starters: overload NC contact wired to PLC input for fault monitoring and alarm generation
Example
In a standard IEC DOL motor starter wiring diagram, the overload relay NC contact (terminals 95-96) is wired in series between the Stop push button (NC, terminals 11-12) and the main contactor coil (A1-A2). Under normal operation the contact is closed and the motor runs; when the motor overloads (e.g. from a mechanical jam), the overload relay trips, opening the 95-96 NC contact, de-energising the contactor coil, and disconnecting the motor from the 3-phase supply.
Key facts
- The Overload Contact NC (normally closed) represents the trip contact of a thermal or electronic overload relay; it is closed during normal motor operation and opens when the relay detects an overcurrent condition.
- IEC 60947-4-1 assigns terminal numbers 95 (In) and 96 (Out) to the NC auxiliary trip contact of an overload relay; these are the standard terminal designations used in IEC motor starter wiring diagrams.
- In a DOL motor starter control circuit, the overload NC contact is wired in series with the Stop push button and the contactor coil: opening the NC contact (on trip) de-energises the coil and stops the motor.
- The overload NC contact remains open after tripping until the overload relay is reset — either manually (by pressing the reset button) or automatically after a cool-down period (if set to auto-reset mode).
- IEC 60617-07 defines the normally-closed contact symbol used for overload relay contacts; the symbol includes a break-contact with a trip actuator marker distinguishing it from a plain NC switch contact.
- Overload relay trip classes (IEC 60947-4-1): Class 10 trips in ≤10 s at 7.2× rated current; Class 20 trips in ≤20 s; Class 30 in ≤30 s — the class is chosen to match motor starting characteristics.
- The reference designator for an overload relay in IEC schematics is OL or F (e.g. F1, OL1); in ANSI/NEMA practice the designator is OL or the thermal overload relay is designated as part of the motor starter assembly (MS1).
Frequently asked questions
What does the overload contact NC symbol look like?
The Overload Contact NC symbol is drawn as a normally-closed contact — two short parallel lines representing contact blades in the closed position — with an additional trip actuator indicator (a small diagonal line or 'OL' label) showing it is the trip contact of an overload relay. In IEC 60617-07 schematics, the NC break-contact symbol is combined with a thermal element qualifier.
What does the NC overload contact do in a motor starter circuit?
The NC overload contact is wired in series with the motor contactor coil control circuit. Under normal operation it is closed, keeping the contactor energised and the motor running. When the overload relay trips (detecting excess motor current), the NC contact opens, de-energising the contactor coil, which disconnects the motor from the power supply and stops it safely.
What are the terminal numbers for the overload relay NC contact?
IEC 60947-4-1 assigns terminal numbers 95 and 96 to the normally-closed (NC) trip contact of an overload relay. Terminal 95 is the input (In) and terminal 96 is the output (Out). These terminal numbers are standardised across IEC-compliant overload relays from all manufacturers and appear in IEC motor starter wiring diagrams.
What is the difference between the overload NC contact and overload NO contact?
The overload NC contact (terminals 95-96) is closed during normal operation and opens when the relay trips. The overload NO contact (terminals 97-98) is open during normal operation and closes when the relay trips. The NC contact is used in the contactor coil circuit to stop the motor on trip; the NO contact is used to signal the trip condition to a PLC or annunciator panel.
What standard defines the overload relay NC contact symbol?
IEC 60617-07 defines the normally-closed contact symbol used for overload relay trip contacts in IEC schematics. IEC 60947-4-1 specifies the performance, terminal numbering (95-96 for NC), and trip class requirements for overload relays. ANSI Y32.2/IEEE 315 defines the equivalent break-contact symbol used in North American motor starter schematics.
How do I reset an overload relay after it trips?
After an overload relay trips and opens the NC contact, pressing the relay's reset button (after the overload cause has been resolved and the relay bimetallic element or electronic circuit has cooled or reset) re-closes the NC contact, allowing the contactor coil to be re-energised and the motor restarted. Automatic reset mode (if enabled) closes the contact after a timed cool-down period without manual intervention — though manual reset mode is preferred for safety in most industrial installations.
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