HP 9000 rp5400 Servers - Manual (Page 146)

NOTE: The green wire ground conductor mentioned above may be a black wire marked with
green tape. [LAHJ]
Computer Safety Ground
Ground all computer equipment with the green (green/yellow) wire included in the branch
circuitry. The green (green/yellow) wire ground conductors should be connected to the appropriate
power panel and should be sized per applicable codes (based on circuit over current device
ratings).
Cabinet Performance Grounding (High Frequency Ground)
Signal interconnects between system cabinets require high frequency ground return paths.
Connect all cabinets to site ground.
NOTE: In some cases power distribution system green (green/yellow) wire ground conductors
are too long and inductive to provide adequate high frequency ground return paths. Therefore,
a ground strap (customer-supplied) should be used for connecting the system cabinet to the site
grounding grid (customer-supplied). When connecting this ground, ensure that the raised floor
is properly grounded for high frequency.
Power panels located in close proximity to the computer equipment should also be connected
to the site grounding grid. Methods of providing a sufficiently high frequency ground grid are
described in the next sections.
Raised Floor "High Frequency Noise" Grounding
If a raised floor system is used, install a complete signal grounding grid for maintaining equal
potential over a broad band of frequencies. The grounding grid should be connected to the
equipment cabinet and electrical service entrance ground at multiple connection points using a
minimum #6 AWG (16mm2) wire ground conductor. The following figure illustrates a metallic
strip grounding system.
Hewlett-Packard recommends the following approaches:
•
Excellent—Add a grounding grid to the subfloor. The grounding grid should be made of
copper strips mounted to the subfloor. The strips should be 0.032 in. (0.08 cm) thick and a
minimum of 3.0 in. (8.0 cm) wide.
Connect each pedestal to four strips using 1/4 in. (6.0 mm) bolts tightened to the
manufacturer's torque recommendation.
• Better - A grounded #6 AWG minimum copper wire grid mechanically clamped to floor
pedestals and properly bonded to the building/site ground.
• Good—Use the raised floor structure as a ground grid. In this case, the floor must be designed
as a ground grid with bolted down stringers and corrosion resistive plating (to provide low
resistance and attachment points for connection to service entrance ground and hp computer
equipment). The use of conductive floor tiles with this style of grid further enhances ground
performance.
146 General Site Preparation Guidelines