To help ensure safety and reliable operation, you should
check the ac outlets. Use the procedure in this section to perform
this task.
Before you begin, ensure that you have a multimeter to check
voltages and an appropriately approved ground-impedance tester to
test the grounding resistances.
Note: Use only an appropriately approved
ground-impedance tester to test the grounding resistances. Do not
use a multimeter to measure grounding resistance.
Before plugging the rack into the ac power source, complete
the following checks on the ac power source:
- Turn off the branch circuit breaker for the ac power outlet
that the rack will plug into. To the circuit breaker switch, attach
tag S229-0237, which reads Do Not Operate.
Note: All
measurements are made with the receptacle faceplate in the usual installed
position.
- Some receptacles are enclosed in
metal housings. For this type of receptacle, complete the following
steps:
- Using a multimeter, check for less than 1 volt from the receptacle
case to any grounded metal structure in the building, such as a raised-floor
metal structure, water pipe, building steel, or similar structure.
- Using a multimeter, check for less than 1 volt from the receptacle
ground pin to a grounded point in the building.
Note: If the receptacle
case or faceplate is painted, be sure the probe tip penetrates the
paint and makes good electrical contact with the metal.
- Using a multimeter, check the resistance from the receptacle ground
pin to the receptacle case. Check resistance from the ground pin to
the building ground. The readings should be less than 1.0 ohm, which
indicates the presence of a continuous grounding conductor.
- If any of the checks made in step 2 are not correct, remove the power
from the branch circuit and make the wiring corrections. Recheck the
receptacle after the wiring is corrected.
- Using a ground-impedance tester, check for infinite resistance
between the ground pin of the receptacle and each of the phase pins.
This is a check for a wiring short to ground or a wiring reversal.
- Using a ground-impedance tester, check for infinite resistance
between the phase pins. This is a check for a wiring short.
- Turn on the branch circuit breaker.
- Using a multimeter, measure for the appropriate voltages
between phases. If no voltage is present on the receptacle case or
grounded pin, the receptacle is safe to touch.
- Using a multimeter, verify that the voltage at the ac outlet
is correct.
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