Electrical Testing of Low Voltage Switchgear, Panelboards & Switchboards (PEARL)

This "How To" electrical testing document is based on PEARL Reconditioning Standard Section 1300, Revision 5 Low Voltage Panelboards, Switchboards & Switchgear, and discusses relevant test equipment as well as suggested procedures and practices to ensure the quality, safety, and speed of your test-for-reconditioning practices.

Introduction:
The section of the PEARL Reconditioning standards covers the following several low-voltage devices including circuit breaker panelboards, switchboards and switchgear, and motor control centers. Although these devices are different in function, the inspection, reconditioning, and testing of all of these devices have enough in common that PEARL believes in appropriate to group them together under section 1300.

Test Equipment:
The following test equipment is required to perform the testing portion PEARL standards related to low voltage circuit breakers:

1. Insulation Resistance Test Set (Megohmeter) 1000 Vdc minimum
2. High Current Test Set

One of the following pieces of test equipment may be required to perform the testing requirements of this reconditioning standard:

1. AC Voltage Supply
2. AC Current Supply
3. AC 3-Phase Voltage Supply
4. DC Voltage Supply
5. Digital Low Resistance Ohmmeter (DLRO - 10 amp unit is sufficient.)
6. DC Current Source and a Millivoltmeter

Test Reference Tables:
To adequately test the electrical properties of the switchgear, panelboards or switchboards, you will also need the following technical reference documents, which can be found in the PEARL Reconditioning Standards:

1. US Standard bus connection bolt torque values (PEARL Reconditioning Standard 6001, Table 1)
2. Insulation resistance and test values for electrical apparatus (PEARL Reconditioning Standard 6002, Table 2)
3. Insulation resistance and test temperature conversion to 20°C value (PEARL Reconditioning Standard 6011, Table 11)

Testing TIPS:

• Panelboards are tested very much like a disconnect switches are tested, including the test of resistance along current carrying path.
• It is very that the insulation between the current carriers and enclosure is solid and that nothing is escaping to a ground outside the carrying path.
• Don't trust visual inspection as the sole inspection of insulation; a shaving, or crack in a fiberglass or epoxy insulator that is hidden from view can result in a short circuit and leave users exposed to danger.
• Occasionally, new replacement insulators can have hidden cracks, resulting in hours of troubleshooting of a completed panelboard or switchgear. It is prudent to test replacement insulators before installation.
• For motor controls, test each component and subassembly, including transformers, circuit breakers, magnetic contactors, and starters, which can also include integral overload devices that require testing.

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