Dielectric Test

Purpose:
To determine the effectiveness of electrical components insulation. The dielectric test verifies the integrity of all branch circuits.

Equipment:
AC or DC Dielectric Tester. The plant may choose to use either an AC or a DC test

Preparation:
The test is performed after all branch circuits and wiring work are completed. All circuit breakers and switches are kept in the “on” position. In the AC dielectric test, water heater, furnace, and any other similar appliances are kept disconnected. For the DC dielectric test, direct-wired appliances (except electric water heaters), smoke alarms, motion detectors and fluorescent light fixtures may remain connected. In order to ovoid electrocution, it is important to make sure no one is working on, or is in contact with any metal substance that may become energized.

Procedure:
The dielectric test is applied by injecting high voltage to the electrical system and monitoring current drop with the use of dielectric tester. The wiring system shall resist current drop when 1080 to 1250 volts-ac (1527 to 1768 volts-dc) is applied for a minimum of one second, not to exceed three seconds; or alternatively, when 900 to 1079 volts-ac (1273 to 1526 volts-dc) is applied for a minimum of 60 seconds, not to exceed two minutes. Fixtures and other appliances are not required to withstand the dielectric strength test. However, the test is performed after they are installed and branch circuits are complete.