Section 4—Performance Tests for PowerPacT Circuit Breakers

Severe environmental conditions can reduce the dielectric strength of molded case circuit breakers. Check insulation resistance during electrical system testing. To check the insulation resistance, perform the following steps:

1. De-energize and isolate the circuit breaker.

2. Clean the circuit breaker as described earlier.

3. Using a megohmmeter with a capacity of 500 -1000 Vdc, apply voltage from: a. Each phase-to-ground with the circuit breaker on (circuit breaker contacts closed). b. Phase-to-phase with the circuit breaker on (circuit breaker contacts closed). c. Between each line and load terminal with the circuit breaker off (circuit breaker contacts open).

4. Record resistance values. Resistance values of less than one megohm (1,000,000 ohm) should be investigated.

Circuit breakers with MicroLogic trip units can have their trip unit operation tested with secondary injection testing using the one of the available test kits. (See Section 6—Available Test Equipment for available test kits by circuit breaker.)

Secondary injection testing does not test the current transformers and connections. Primary injection testing can be used to ensure that all trip system connections have been correctly made.

If the circuit breaker is tested by the primary injection method, the PowerLogic™ system can remain connected to the circuit breaker during testing without affecting the results.

Zone-selective interlocking (ZSI) is a method of communication between electronic-trip overcurrent protective devices. ZSI allows interlocked devices at different levels to work together as a system in which a short circuit or ground fault is isolated and cleared with minimum time delay. The purpose of defeating ZSI is to verify the characteristics of the specific circuit breaker short-time and ground-fault trip delay functions.

MicroLogic electronic-trip circuit breakers with the integral ground-fault protection function require special attention when testing overload and short-circuit functions. The single-pole primary injection tests for the inverse-time overcurrent, short-time and instantaneous functions will cause ground-fault trips due to the return current path not going through the circuit breaker. To overcome this difficulty, use the Hand-Held, Full-Function, or UTA Test Kit to defeat the ground-fault function on PowerPacT circuit breakers equipped with MicroLogic trip units.

DANGER

Hazard of Electric Shock, explosion, or Arc Flash Apply appropriate personal protective equipment (PPE) and follow safe electrical work practices. See NFPA 70E or CSA Z462. This equipment must be installed and serviced by qualified electrical personnel. Turn off all power supplying this equipment before working on or inside equipment. Always use a properly rated voltage sensing device to confirm power is off. Replace all devices, doors and covers before turning on power to this equipment. Failure to follow these instructions will result in death or serious injury.

Ground-Fault Trip Test

The ground-fault function of a MicroLogic electronic-trip circuit breaker provides ground-fault protection for equipment with adjustable pickup and delay values. the ground-fault delay feature determines how long the circuit breaker waits before initiating a trip signal during a ground fault. Performance of the ground-fault functions of the circuit breaker can be tested using a high-current, low-voltage ac power supply.

Test Procedure

1. Completely de-energize and remove the circuit breaker from service.

2. Before testing, record pickup and delay setting for all functions. Reset the trip unit to these same settings after the test procedure is completed.

3. If testing a circuit breaker that is equipped with zone-selective interlocking, follow the procedure to defeat zone-selective interlocking on Procedure to Defeat Zone-Selective Interlocking. If you are using a secondary injection test kit for these tests, carefully read and follow the test kit instructions about zone-selective interlocking.

   NOTE: Failure to defeat zone-selective interlocking will result in trip time inaccuracy.

4. Use these settings for the test:

   Long-time Pickup/Ampere Rating = Max.

   Long-time/Overload Delay = Max

   Short-time/Short-circuit Delay = Max. (I²t IN or ON)

   Instantaneous = Max.

   Ground-fault Pickup = Min.

   Ground-fault Delay = 0.2

5. Follow the hookup procedure appropriate to the test application.

   For circuit breakers without a neutral current transformer, go to step 8.

   For circuit breakers with the integral ground-fault function in a three-phase, four-wire system, an externally-mounted neutral current transformer (CT) must be used. The neutral CT is connected to the circuit breaker by a shielded cable (14 AWG [2.1 mm²] wire is recommended).

   NOTE: When testing, disconnect or turn off 24 Vdc control power to F1 and F2, if equipped and disconnect the Hand-Held or Full-Function Test Kit from the trip unit, if connected.

   Test Hookup Diagram for Neutral CT Phasing Test See circuit breaker instructions bulletin for connections to circuit breaker and neutral CT.

   Test Hookup Diagram for Neutral CTSize Test See circuit breaker instructions bulletin for connections to circuit breaker and neutral CT.

6. Verify correct phasing of the neutral CT (three-phase, four-wire systems) by performing a No Trip Test as follows:

   1. Connect the circuit breaker and neutral CT as shown in Test Hookup Diagram for Neutral CT Phasing Test. The jumper must go from the load connection on the circuit breaker to the H1 connection on the neutral CT (or the side of the neutral CT that has the red dot). Connect the secondary of the neutral CT according to the circuit breaker instruction manual or the neutral CT instructions.

   2. Apply current above the ground-fault pickup level and maintain longer than the ground-fault delay.

   3. The circuit breaker must not trip. No trip indicates that both the phase CT and neutral CT are phased properly.

7. Test Hookup Diagram for Circuit Breaker Without Neutral CT

   Test Hookup Diagram for Ground-Fault Pickup and Delay Test

   Verify the correct size of the neutral CT (three-phase, four-wire systems) by performing a Trip Test as follows:

   1. Connect the circuit breaker and neutral CT as shown in Test Hookup Diagram for Neutral CTSize Test. Connect the polarity (+) terminal of the high current injection unit to the load side of the circuit breaker. The jumper must go from the line connection on the circuit breaker to the H1 connection on the neutral CT (or the side of the neutral CT that has the red dot). Connect the non-polarity (-) terminal of the high current injection unit to H2 on the neutral CT (on the line side of the circuit breaker). Connect the secondary of the neutral CT according to the circuit breaker instruction manual or the neutral CT instructions.

   2. Apply current.

   3. The circuit breaker must trip at half the value of the ground-fault pickup. Tripping indicates that both the phase CT and neutral CT have the same turns ratio (same size).

8. Test ground fault pickup and delay by performing a trip test as follows:

   1. Connect the circuit breaker as shown in Test Hookup Diagram for Circuit Breaker Without Neutral CT, (three-phase, three-wire systems) or Test Hookup Diagram for Ground-Fault Pickup and Delay Test (three-phase, four-wire systems).

      NOTE: The recommended method of testing ground-fault pickup and delay is the “pulse” method. This method will be the most accurate, but requires that the test equipment have a calibrated image-retaining oscilloscope or high-speed sampling rate digital ammeter. An accurate timer is needed to monitor delay time.

   2. After the circuit is properly connected and closed, apply current in short pulses of 10-cycle duration. Starting at 70% of the expected trip value, increase the current on each succeeding pulse until the circuit breaker trips.

   3. Reclose the circuit breaker and reduce the current level; pulse again to determine if the pickup level found was overshot.

   4. Repeat steps b and c to further isolate the pickup point.

   5. To determine delay time, test each pole of the circuit breaker individually at 150% of the ground-fault pickup setting. Monitor the time from this pickup point until the circuit breaker trips to obtain the delay time.

   6. Record pickup and delay values and compare the results to the trip curve.

The ground-fault test can also be done using secondary injection testing using the Full-Function Test Kit. Secondary injection testing does not test the current transformers and connections.

Contact Resistance Test

Circuit breaker pole resistance tests are not reliable indicators of circuit breaker performance because the resistance values are influenced by a number of transient factors including contact surface oxidation, foreign material between the contacts, and testing methods. NEMA AB 4 paragraph 6.4.1 states: “The millivolt drop of a circuit breaker pole can vary significantly due to inherent variability in the extreme low resistance of the electrical contacts and connectors. Such variations do not necessarily predict unacceptable performance and shall not be used as the sole criteria for determination of acceptability.”

High pole resistance may also be caused by eroded contacts, low contact force, and loose termination. The only one of these factors likely to be present on a new circuit breaker is a loose termination, since the contacts are new and there has been no opportunity for contact pressure to have drifted from the factory setting. A loose termination can be corrected in the field.

If a contact resistance test is done, it is important to do it after the contacts have been conditioned by instantaneous primary injection testing to ensure the contacts are clear of resistive films, oxidation and foreign material. If the circuit breaker has been in service with no performance issues, (overheating or nuisance tripping), contact resistance measurements are redundant and of little value.

Square D recommends that a DLRO (Digital Low Resistance Ohmmeter) be used, using a 10 A dc test current for circuit breaker ratings below 100 A, and using 100 A dc for circuit breakers rated 100 A and above. the median (middle) value of three readings (toggling the circuit breaker between each reading) should be recorded for each pole tested. If this value is equal to or less than the value listed in Maximum Micro-Ohms Per Pole, the pole is acceptable. If the reading is higher, the cause should be investigated and corrected if possible. Contact your local field office for more information.