Cooling fan
Common VFD, drive, UPS, and cabinet overheating failure point.
Square D Circuit Breaker Fault Codes - Quick Reference
Square D (Schneider Electric) Masterpact NT/NW and Powerpact H/J/L frame breakers use Micrologic trip units that display fault codes via LED indicators and the trip cause button. Older QO and QOB residential breakers use a mechanical trip indicator only.
| Fault / LED | Meaning | Quick Fix |
|---|---|---|
| Trip - Overload (OL) | Long-time overcurrent | Reduce load, reset after cooling |
| Trip - Short Circuit (SC) | Instantaneous fault current | Find and clear fault, inspect breaker |
| Trip - Ground Fault (GF) | Earth fault detected | Locate ground fault, test insulation |
| Trip - Earth Leakage | Micrologic 6/7 - leakage trip | Check for ground faults |
| Trip - Long Time Memory | Accumulated overload | Reduce load |
| ALARM: Overload warning | Load approaching trip threshold | Reduce current draw |
| ALARM: Maintenance | Breaker at contact wear limit | Schedule replacement |
| ALARM: Communication | Micrologic bus fault | Check wiring to building management |
| 50Hz / 60Hz mismatch | Wrong frequency setting | Adjust Micrologic frequency setting |
| Micrologic - No Communication | BSCM module fault | Check module and wiring |
Most Common Faults
Overload Trip
An OL trip on a Masterpact means load current exceeded the long-time protection setting (Ir × In) for the required time (tr). Check actual amperage on all three phases with a clamp meter. If all phases are within rated current, check the Ir and tr settings on the Micrologic unit - they may have been set incorrectly.
Short Circuit Trip
An SC trip is immediate and occurs on fault currents above the magnetic threshold (Im setting). After an SC trip, visually inspect the load-side wiring, the load itself, and the breaker contacts. Do not immediately reset without locating the fault - repeated SC trips damage the breaker arc chutes.
Ground Fault Trip
Micrologic 5, 6, and 7 trip units include ground fault protection. A GF trip indicates current flowing to ground - typically from insulation failure, a wet connection, or equipment with a shorted winding. Use a megohmmeter to test insulation resistance on connected cables and equipment.
Maintenance Alarm
Masterpact breakers track contact wear via operating cycles. When the contact wear limit is reached, a maintenance alarm signals that the breaker should be inspected by a qualified electrical technician. Do not continue running without service.
Parts Often Needed
| Part | Notes |
|---|---|
| Micrologic trip unit | Replacement when electronics fail |
| Arc chutes | Replace after multiple SC trips |
| BSCM communication module | Replace on communication fault |
| Auxiliary contact blocks | Replace on worn auxiliary contacts |
| Breaker body (NW/NT) | Replace at end of contact life |
Need Replacement Parts?
Before ordering, match the breaker part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
Circuit breaker maintenance and replacement in 400A–6300A switchgear requires a licensed electrician. Do not reset a breaker after a short circuit trip without inspecting the load circuit thoroughly.