if a wire with primary voltage on it is swapped with the ground wire, causing an electrical shock
hazard. Use the procedures for checking receptacles in Electrical Safety for IBM Service
Representatives, S229-8124.
6. For each unit, check continuity from a conductive area on the frame to the ground pin on the plug. Do
this at the end of the mainline ac power cable. The resistance must be 0.1 ohm or less.
7. Ground continuity must be present from each unit receptacle to an effective ground. Therefore, check
the following:
v The ac voltage receptacle for each unit must have a ground wire connected from the ground
terminal on the receptacle to the ground bar in the power panel.
v The ground bars in all branch circuit panels must be connected with an insulated ground wire to a
ground point, which is defined as follows:
– The nearest available metal cold water pipe, only if the pipe is effectively grounded to the earth
(see National Electric Code Section 250-81, in the United States).
– The nearest available steel beams in the building structure, only if the beam is effectively
grounded to the earth.
– Steel bars in the base of the building or a metal ground ring that is around the building under
the surface of the earth.
– A ground rod in the earth (see National Electric Code Section 250-83, in the United States).
Note: For installations in the United States only, by National Electrical Code standard, if more than
one of the preceding grounding methods are used, they must be connected together electrically.
See National Electric Code Section 250, for more information on grounding.
v The grounds of all separately derived sources (uninterruptable power supply, service entrance
transformer, system power module, motor generator) must be connected to a ground point as
defined above.
v The service entrance ground bar must connect to a ground point as defined above.
v All ground connections must be tight.
v Check continuity of the ground path for each unit that is using an ECOS tester, Model 1023-100.
Check continuity at each unit receptacle, and measure to the ground point as defined above. The
total resistance of each ground path must be 1.0 ohm or less. If you cannot meet this requirement,
check for faults in the ground path.
v Conduit is sometimes used to meet wiring code requirements. If conduit is used, the branch circuits
must still have a green (or green and yellow) wire for grounding as stated above.
Note: The ground bar and the neutral bar must never be connected together in branch circuit
power panels.
The ground bar and the neutral bar in the power panels that make up the electrical power network
for the server must be connected together. This applies to the first electrically isolating unit that is
found in the path of electrical wiring from the server to the service entrance power panel. This
isolating unit is sometimes referred to as a separately derived source. It can be an
uninterruptable power supply, the system power module for the system, or the service entrance
transformer. If the building has none of the above isolating units, the ground bar and the neutral
bar must be connected together in the service entrance power panel.
8. Look inside all power panels to ensure the following:
v There is a separate ground wire for each unit.
v The green (or green and yellow) ground wires are connected only to the ground bar.
v The ground bar inside each power panel is connected to the frame of the panel.
v The neutral wires are connected only to the neutral bar.
v The ground bar and the neutral bar are not connected together, except as stated in step 7 (See
page 111) of this procedure.
Analyze hardware problems 111
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