Overload Contact NO Symbol
Definition: The Overload Contact NO symbol represents a normally-open (NO) auxiliary contact of a thermal or electronic overload relay — standardised in IEC 60617-07 and ANSI Y32.2/IEEE 315 — which is open under normal (non-tripped) conditions and closes when the overload relay trips due to excess motor current, with terminal designations In (pin 97) and Out (pin 98) per IEC 60947-4-1.
Also known as: overload NO contact, OL NO, normally open overload contact, overload alarm contact, 97-98 contact, overload trip signal contact.
What the Overload Contact NO symbol means
The Overload Contact NO (normally open) symbol represents the auxiliary alarm or signal contact of an overload relay that is open during normal motor operation and closes when the overload relay trips due to detected overcurrent. Unlike the NC contact (95-96) which directly interrupts the contactor coil circuit, the NO contact (97-98) is primarily used for signalling, fault indication, and monitoring purposes.
In IEC industrial control circuit diagrams, the overload NO contact is connected to pilot lights, alarm bells, PLC digital inputs, or SCADA systems to indicate a trip event. When the overload relay trips — due to sustained overcurrent, phase loss, or thermistor input — the NO contact closes, completing the alarm or monitoring circuit. The contact remains closed until the overload relay is manually or automatically reset.
How to identify the Overload Contact NO symbol
The Overload Contact NO symbol is drawn as two horizontal parallel lines with a gap between them (representing the open contact blades), combined with an overload trip indicator — a diagonal line, small rectangle, or 'OL' annotation above the contact symbol. In IEC 60617-07 notation, the make-contact symbol is shown with a trip actuator qualifier marking it as the NO auxiliary contact of an overload relay. ANSI schematics use a make-contact symbol with an OL designator or separate overload coil reference.
Function in a circuit
The overload NO contact provides a signal output when the overload relay trips. During normal motor operation, the NO contact is open and does not conduct. When the overload relay detects a current exceeding its set trip level for the required trip time, the internal mechanism simultaneously opens the NC contact (95-96, stopping the motor) and closes the NO contact (97-98). This closure of the NO contact can energise a fault indicator light, trigger a PLC alarm input, activate an audible warning, or log the trip event in a SCADA system. The NO contact indicates the trip state but does not itself stop the motor.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-07 defines the normally-open (make) contact symbol. IEC 60947-4-1 specifies overload relay auxiliary contacts and assigns terminal numbers 97 (In) and 98 (Out) to the NO auxiliary contact. The IEC symbol combines the make-contact with a trip actuator qualifier. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 uses a make-contact symbol (two lines with a gap) plus an overload designator or coil reference for the NO overload contact. NEMA ICS standards govern the contact rating and performance requirements for North American overload relays. |
| Key difference | IEC 60617-07 and ANSI Y32.2/IEEE 315 NO overload contact symbols differ in detail: IEC uses the make-contact with a trip actuator marker; ANSI uses the make-contact with an 'OL' annotation or reference to the overload relay coil. Both indicate the same function — a contact that closes 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: 97 (In) and 98 (Out) per IEC 60947-4-1. Trip current range: adjustable, same range as the associated overload relay (0.1 A to 100 A). Reset: manual or automatic (same reset mechanism as NC contact). Contact voltage rating: typically 250 V AC / 24 V DC.
Where the Overload Contact NO symbol is used
- PLC digital input wiring: overload NO contact connected to PLC input module to signal trip event for alarm and logging
- Pilot fault light: NO contact in series with a panel-mounted red fault indicator lamp energised on overload trip
- SCADA and BMS: NO contact wired to monitoring system input for remote trip status display
- Audible alarm: NO contact closes to activate a buzzer or horn on motor overload trip
- DOL starter fault circuit: NO contact provides latched fault indication alongside the NC stop-circuit contact
- Multi-motor coordination: NO contact signal from one motor overload relay used to stop an associated upstream or downstream machine
Example
In a pump control panel wiring diagram, the overload relay NO contact (terminals 97-98) is wired in series with a 24 V DC PLC input module channel (I1) and the +24 V supply: when the pump motor overloads and the overload relay trips, the NO contact closes, energising the PLC input and triggering a fault alarm message on the HMI panel while the NC contact (95-96) simultaneously de-energises the contactor coil to stop the pump.
Key facts
- The Overload Contact NO (normally open) represents the signal/alarm auxiliary contact of an overload relay; it is open during normal motor operation and closes when the relay detects an overcurrent trip condition.
- IEC 60947-4-1 assigns terminal numbers 97 (In) and 98 (Out) to the normally-open (NO) auxiliary contact of an overload relay, standardised across all IEC-compliant overload relay manufacturers.
- The overload NO contact (97-98) is used for signalling and alarm purposes; it does not itself stop the motor. The NC contact (95-96) de-energises the contactor coil to stop the motor.
- When the overload relay trips, both contacts change state simultaneously: the NC contact (95-96) opens and the NO contact (97-98) closes — this is the standard operation of IEC thermal and electronic overload relays.
- The NO contact is commonly wired to a PLC digital input, a fault indicator lamp, or an audible alarm to notify operators of a motor overload trip event.
- IEC 60617-07 defines the normally-open (make) contact symbol; combined with an overload actuator qualifier, it distinguishes the overload NO contact from a plain switch or relay make-contact in industrial schematics.
- The reference designator for an overload relay in IEC schematics is F or OL (e.g. F1, OL1); both the NC contact (95-96) and NO contact (97-98) are associated with the same overload relay designator.
Frequently asked questions
What does the overload contact NO symbol look like?
The Overload Contact NO symbol is drawn as a normally-open contact — two short parallel lines with a gap between them representing the open contact blades — with an overload trip actuator indicator (a small diagonal bar or 'OL' label) showing it belongs to an overload relay. In IEC 60617-07 schematics, the make-contact symbol is combined with a trip actuator qualifier.
What does the NO overload contact do in a motor control circuit?
The NO overload contact (terminals 97-98) is open during normal motor operation and closes when the overload relay trips. It is used to signal the trip event to a PLC, fault indicator light, or alarm system. The NO contact does not itself stop the motor — that function is performed by the NC contact (95-96) which interrupts the contactor coil circuit.
What are the terminal numbers for the overload relay NO contact?
IEC 60947-4-1 assigns terminal numbers 97 and 98 to the normally-open (NO) auxiliary contact of an overload relay. Terminal 97 is the input (In) and terminal 98 is the output (Out). These are standardised terminal numbers used across IEC-compliant overload relays and motor starter wiring diagrams worldwide.
What is the difference between the overload NO and NC contacts?
The overload NC contact (terminals 95-96) is closed during normal operation and opens on trip, interrupting the contactor coil circuit to stop the motor. The overload NO contact (terminals 97-98) is open during normal operation and closes on trip, used to signal the fault to a PLC, alarm, or indicator lamp. Both contacts change state simultaneously when the overload relay trips.
What standard defines the overload relay NO contact symbol?
IEC 60617-07 defines the normally-open (make) contact symbol used for overload relay auxiliary contacts in IEC schematics. IEC 60947-4-1 specifies overload relay terminal numbering (97-98 for NO contact) and performance requirements. ANSI Y32.2/IEEE 315 defines the equivalent make-contact symbol for North American motor control schematics.
Can the overload NO contact be used to latch a fault condition?
Yes. In motor control circuits, the overload NO contact (97-98) is commonly wired to a PLC input or a latching relay circuit so that a trip event is recorded and acknowledged by an operator before reset. The NO contact holds closed until the overload relay is manually reset (or auto-resets after cool-down), providing a sustained fault signal for monitoring and logging purposes.
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