Checking customer ground continuity with customer CB off (wired)

Procedure

  1. Prepare the multimeter to measure 1.0 V ac or less.
  2. Measure the voltage on the female ground pin  C  (single-phase, Figure 1) or "Ground" (three-phase, Figure 2) on each mainline power cable connector (at DC-UPS end) and building ground.

    Is the voltage less than 1.0 V ac?

    • Yes, go to step 4.
    • No, continue at the following step.
    Figure 1. Single-phase mainline power connector at DC-UPS end
    Single-phase mainline power connector at DC-UPS end
    Figure 2. Three-phase high voltage (380 - 415 V) mainline power connector at DC-UPS end
    Three-phase wye mainline power connector
  3. Voltage is present at a customer outlet with the customer circuit breakers off.
    DANGER
    Inform the customer that even though the circuit breaker is off, voltage higher than 1.0 V ac is measured at the failing customer voltage outlet pins.

    Do not continue until the voltage is less than 1.0 V ac.

  4. Prepare the multimeter to measure 1.0 ohm or less of resistance.
  5. Measure the resistance between the female connector ground pin on each mainline power cable and the building ground.

    Is the resistance 1.0 ohm or less?

    • Yes, continue with the next section.
    • No, inform the customer. Do not continue until the resistance is 1.0 ohm or less.