General Site Preparation Guidelines
Electrical Factors
Chapter 2
23
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 and yellow) wire included in the branch circuitry. The
green (green and 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).
Dual Power Source Grounding
When dual power sources are utilized, strong consideration should be given to measure voltage potentials.
The use of dual power might create an electrical potential that can be harmful to personnel and might cause
performance issues for the equipment.
Dual power sources might originate from two different transformers or two different UPS devices. Voltage
potentials from ground pin to ground pin of these sources should be measured and verified to be at or near 0.0
volts. Voltage levels that deviate or are measured above 3.0 volts should be further investigated. Increased
voltages might be harmful to personnel, and should be further investigated.
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 and 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 3-1 illustrates a metallic strip grounding system.
NOTE
Regardless of the grounding connection method used, the raised floor should be grounded as an
absolute safety minimum.
HP 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
