IBM 7012 300 Series Installation And Service Manual page 121

Step 3. Checking Customer Outlets
Note: For a translation of the following notices, see System Unit Safety Information , Order
CAUTION:
Do not touch the receptacle or the receptacle faceplate with anything other than your
test probes before you have met the requirement in step 8.
1. Have the customer locate and turn off the branch circuit CB (circuit breaker). (Attach tag
S229-0237, which reads "Do Not Operate.")
Note: All measurements are made with the receptacle faceplate in its normal installed
2. Some receptacles are enclosed in metal housings. On receptacles of this type, perform
the following steps:
a. Check for less than 1 volt from the receptacle case to any grounded metal structure in
b. Check for less than 1 volt from receptacle ground pin to a grounded point in the
Note: If the receptacle case or faceplate is painted, be sure the probe tip penetrates the
c. Check the resistance from ground pin of the receptacle to the receptacle case. Check
3. If any of the three checks made in step 2 are not correct, ask the customer to remove the
power from the branch circuit and make the wiring corrections; then check the receptacle
again.
Note: Do not use the digital multimeter to measure grounding resistance.
4. 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.
5. Check for infinite resistance between phase pins. This is a check for a wiring short.
CAUTION:
If the reading is other than infinity, do not proceed. Have the customer make
necessary wiring corrections before continuing. Do not turn on the branch circuit CB
until all the above steps are satisfactorily completed.
6. Have the customer turn on the branch circuit CB. Measure for appropriate voltages
between phases. If no voltage is present on the receptacle case or grounded pin, the
receptacle is safe to touch.
7. With an appropriate meter, verify that the voltage at the outlet is correct.
8. Verify that the grounding impedance is correct by using the ECOS 1020, 1023, B7106,
C7106, or an appropriately approved ground impedance tester.
Note: Do not use the 120-volt convenience outlets inside a machine to power the tester.
Number SA23-2652.
position.
the building, such as a raised floor metal structure, water pipe, building steel, or
similar structure.
building.
paint and makes good electrical contact with the metal.
resistance from ground pin to building ground. The reading should be less than 1.0
ohm, which indicates the presence of a continuous grounding conductor.
4-3
System Installation