Section 1—Introduction
Inspection and Testing
The service life of molded case circuit breakers depends on proper application, correct installation, environmental conditions and preventive maintenance. Two levels of investigation can ensure that a circuit breaker is able to operate properly:
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Inspection and preventive maintenance.
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Performance and verification tests.
To ensure continued suitable performance, periodically inspect the circuit breakers following the procedures outlined in this document. These test procedures will help diagnose operational problems and are provided as an aid or as follow-up to an inspection that reveals potential problems. The inspection, preventive maintenance, and field-testing instructions provided in this document are intended for use with electronic-trip molded-case circuit breakers with the MicroLogic trip system, thermal-magnetic circuit breakers, and magnetic-only circuit breakers.
Circuit Breaker Inspection and Testing
| Circuit Breaker Type | Inspection | Performance Tests |
|---|---|---|
| Thermal-Magnetic Circuit Breakers | Section 2 | Section 3 |
| Magnetic-Only Circuit Breakers | Section 2 | Section 3 |
| PowerPacT Circuit Breakers | Section 2 | Section 4 |
| Electronic Trip (Except for MasterPacT and PowerPacT) Circuit Breakers | Section 2 | Section 5 |
For information on maintenance and testing of insulated case MasterPacT circuit breakers, see bulletin 0613IB1202, Maintenance and Field Testing Guide for MasterPacT NT and NW Circuit Breakers.
The standard generally used as a basis for field-testing requirements is the National Electrical Manufacturers Association Standard, NEMA AB 4, “Guidelines for Inspection and Preventive Maintenance of Molded Case Circuit Breakers Used in Commercial and Industrial Applications.” If additional information or assistance is required, contact your local field sales office. For on-site service, contact the Customer Information Center twenty-four hours a day at 1-888-778-2733.
The inspection and preventive maintenance procedures outlined in this publication may be useful in setting up a routine inspection program. Conduct performance tests only if inspection or daily operation indicates that a circuit breaker may not be adequately providing the protection required by its application.
If questionable results are observed during inspection or performance tests, consult your local field sales office. If it is necessary to return a circuit breaker to the manufacturing facility, use proper packaging and packing materials to avoid shipping damage.
This publication is not intended, nor is it adequate, to verify proper electrical performance of a molded case circuit breaker that has been disassembled, modified, rebuilt, refurbished, or handled in any manner not intended or authorized by Schneider Electric.
Thermal-Magnetic Circuit Breaker Testing Inaccuracies
During the last few years there have been increasing incidents of inaccurate field testing. Major obstacles to accurate field testing of circuit breakers are the variables present in modern installations, such as variations in enclosures, bussing, cabling and proximity to other equipment.
Another obstacle is Vac vs. Vdc test currents for direct current applications. Most manufacturers have tested and certified ac circuit breakers for use in low-voltage dc applications (250 Vdc or less). When applying thermal-magnetic circuit breakers, 1000 A frame or less, on low-voltage (< 250 Vdc systems) the circuit breaker’s thermal characteristics remain unchanged. But the magnetic (instantaneous) characteristics do change and require a multiplier to determine the dc current necessary to trip the circuit breaker. The multipliers for use with Square D™ equipment are shown in the Determining Current Carrying Capacities in Special Applications data bulletin.
For circuit breakers above 1000 A and 500 Vdc circuit breakers, the correlation between ac current and dc current is not predictable. For accurate results, these circuit breakers must be tested using dc current. See Field Testing Special 500 Vdc Circuit Breakers for testing information.
Safety Precautions
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Only qualified electrical workers with training and experience on low-voltage circuits should perform work described in these instructions. Workers must understand the hazards involved in working with or near low-voltage equipment. Such work should be performed only after reading this complete set of instructions.
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Some inspections or procedures require that certain parts of the electrical system remain energized at hazardous voltage during the procedure. Observe all specific safety messages (Danger, Warning, Caution) throughout this manual.
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Wear protective safety equipment, recognize potential hazard, and take adequate safety precautions when performing the procedures outlined in this manual.