ELECTRICAL TESTS MOLDED CASE CIRCUIT BREAKERS
VISUAL AND MECHANICAL INSPECTION
- Check circuit breaker for proper mounting, conductor size and feeder designation.
- Inspect case for cracks or other defects.
- Check tightness of connection with torque wrench in accordance with manufacturer’s recommendations.
- Operate circuit breaker to insure smooth operation.
ELECTRICAL TESTS MOLDED CASE CIRCUIT BREAKERS
- Measure contact resistance. For circuit breakers 600 amps and larger values in excess of 200 micro-ohms or deviation of more than twenty percent (20%) shall be investigated. For circuit breakers less than 600 amps values may be higher and deviation should not any greater than 50%.
- Perform time-current characteristic test by passing three hundred percent (300%) rated current through each pole separately. Record results on field data test sheet. All trip times shall fall within values listed in the attached table, or the circuit breaker shall be replaced.
- Check instantaneous (magnetic) pickup current by run-up of pulse method. Clearing time and pickup current levels should be within manufacturer’s published values.
- Insulation resistance should be determined pole to pole , line to load across pole the pole, and pole to ground. Test voltage shall be 1000 volts DC Insulation resistance shall not be less than (50) fifty megohms.
- Check auxiliary devices that may be supplied i.e., shunt trip, ground fault, under voltage.
RECOMMENDED OVER-CURRENT TRIP TEST VALUES
(at 300 Percent of Rated Continuous Current of Breaker)
| Rated Voltage,
Volts
|
Range of Rated
Continuous Current, Amperes |
Thermal Minimum Tripping Time
Seconds
|
Thermal Maximum Tripping Time Seconds |
Magnetic trip or MCP Trip (instantaneous)
Set and tested at 3X |
| 240 | 15-45 | 3 | 50 | — |
| 240 | 50-100 | 5 | 70 | — |
| 600 | 15-45 | 5 | 80 | — |
| 600 | 50-100 | 5 | 150 | — |
| 240 | 110-225 | 10 | 200 | — |
| 600 | 110-225 | 10 | 200 | — |
| 600 | 250-450 | 25 | 250 | — |
| 600 | 500-600 | 25 | 250 | — |
| 600 | 700-1200 | 25 | 450 | — |
| 600 | 1400-2500 | 25 | 600 | — |
Note: MCP’s only have magnetic pickup. Therefore, only the instantaneous trip is checked. Few circuit breakers rated less that 600 amps have thermal and magnetic trip units. Usually they contain only thermal trip units. Therefore, only the long delay or thermal trip time is checked.
MOLDED CASE CIRCUIT BREAKER TEST DATA
INSULATED CASE CIRCUIT BREAKER TEST DATA
