Overload Contact Symbol Guide: IEC vs NEMA Pinouts & Wiring

When reading a motor control schematic, the overload contact symbol dictates how the control circuit reacts to a thermal or electronic trip event. Unlike main power terminals, these auxiliary contacts handle low-current logic (typically under 10A at 120V AC or 24V DC) to drop out the contactor coil or signal a PLC. Below is the definitive reference for identifying, wiring, and troubleshooting these critical safety components.

Overload Relay Contact Symbols & Terminal Pinouts (IEC vs NEMA)

The table below maps the schematic symbols you will see on prints to the physical terminal numbers stamped on modern IEC-rated relays (like the Schneider TeSys LRD or Siemens SIRIUS 3RU2) and traditional NEMA-rated blocks.

Symbol / Function	IEC Terminal Numbers	NEMA Schematic Representation	Practical Application
NC Overload Trip	95-96	NC (Generic or labeled 'OL')	Wired in series with the contactor coil (A1-A2). Opens upon trip to break the control circuit and drop out the main contactor.
NO Overload Trip	97-98	NO (Generic or labeled 'OL')	Wired to a PLC digital input or a red fault indicator lamp. Closes upon trip to signal a fault condition to the operator or automation system.
Test / Reset Mechanism	N/A (Mechanical)	N/A (Mechanical)	Manual push-button to simulate a trip (Test) or clear the mechanical latch after the bimetallic strip cools (Reset).
Main Power (In/Out)	1-2, 3-4, 5-6 (or L1/T1...)	L1-T1, L2-T2, L3-T3	3-phase motor feed. These are the high-current load paths, not control contacts, but are frequently confused on schematics.

Regional Standard Variants: IEC 60947 vs NEMA ICS 2

How an overload contact symbol is drawn and numbered depends heavily on the governing standard in your region.

IEC 60947-4-1 (Global / Europe / Modern US):
The IEC standard uses a strict, function-specific numbering system. The prefix 9 is exclusively reserved for overload relay auxiliary contacts. Therefore, a 95-96 terminal is universally recognized by IEC-trained technicians as a Normally Closed overload trip contact, while 97-98 is Normally Open. This makes physical wiring and troubleshooting highly predictable, even without a schematic in hand.

NEMA ICS 2 (North America / Legacy):
Traditional NEMA standards (and older US schematics) rely less on physical terminal numbering and more on schematic context. On a NEMA drawing, the overload contact symbol is often just a standard relay contact symbol labeled with the device name (e.g., 'OL1'). The physical NEMA overload block might not even have '95' stamped on it; instead, it relies on the installer following the line numbers on the schematic. Modern NEMA-sized contactors (like Allen-Bradley Bulletin 193) now largely adopt IEC-style 9x stamping for global compatibility, but legacy panels still rely on schematic tracing.

The 'Rows People Get Wrong' Field Guide

When wiring or troubleshooting motor starters, misinterpreting the overload contact symbol leads to nuisance trips or, worse, unprotected motors. Watch out for these specific pitfalls:

• Confusing 13/14 with 97/98: Terminals 13-14 represent a standard Normally Open auxiliary contact on the contactor. Terminals 97-98 represent the NO contact on the overload relay. If the motor trips, the contactor drops out, causing 13-14 to open. However, the overload's 97-98 contact closes to signal the fault. Wiring your PLC fault input to 13-14 instead of 97-98 will result in a PLC logic fault every time the motor stops normally.
• Assuming 95/96 Can Handle Motor Loads: The 95-96 NC contact is rated for control circuit duty (typically 10A at 120V AC, categorized as AC-15). It is not designed to interrupt 30A+ motor starting inrush currents. Always ensure it is only switching the contactor coil (A1-A2), not the main power line.
• Wiring 95-96 in Parallel: The 95-96 NC contact must be wired in series with the contactor coil or the master control circuit. Wiring it in parallel creates a dead short across the coil or bypasses the safety interlock entirely.

Troubleshooting Faded or Missing Overload Markings

On a 15-year-old panel, the ink stamped on the plastic housing of a Furnas or Siemens overload relay often rubs off. If you cannot read the terminal numbers, you can safely identify the 95-96 and 97-98 contacts using a multimeter.

1. De-energize and Lock Out: Turn off the main breaker and verify the circuit is dead with a non-contact voltage tester and a CAT III multimeter.
2. Isolate the Wires: Remove the control wires from the auxiliary terminals to prevent back-feeding through the PLC or contactor coil.
3. Set Meter to Continuity: Use the diode/continuity setting on your multimeter (the one that beeps).
4. Test in 'Reset' State: Ensure the overload is in its normal, un-tripped state. Probe the unknown terminals. The pair that beeps (shows continuity) is your 95-96 NC contact.
5. Test in 'Tripped' State: Use a small flathead screwdriver to press and hold the 'Test' button on the front of the overload relay (this mechanically simulates a trip). Probe the terminals again. The pair that now beeps is your 97-98 NO contact. The pair that was previously beeping will now show open (OL).

Overload Contact Symbol FAQ