HP 9000 Superdome SX2000 Generic Site Preparation Guide - Edition 6 - Page 14

Dual Power Source Grounding, Cabinet Performance Grounding (High-Frequency Intercabinet Ground)

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Dual Power Source Grounding The use of dual power might create an electrical potential that can be hazardous to personnel and might cause performance issues for the equipment. When using dual power sources, measure voltage potentials with a high impedance digital multi-meter (DMM). Dual power sources might originate from two different transformers or two different UPS devices. Measure voltage potentials from ground pin to ground pin of these sources and verify them to be at or near 0.0 V. Investigate voltage levels that measure above 3.0 V because increased voltages can be hazardous to personnel. Cabinet Performance Grounding (High-Frequency Intercabinet Ground) Some safety power distribution wires are too long and too inductive to provide adequate high-frequency return paths. For sufficient protection, signal interconnects between system cabinets might need high-frequency ground return paths in addition to the safety or power distribution system 50-60Hz grounding system. HP recommends the use of a properly installed signal reference grid (SRG) also bonded to the 50-60Hz grounding system. WARNING! Do not use cabinet-to-floor ground straps in place of a properly installed safety (50-60Hz) grounding system, nor in place of a properly installed Signal Reference Grid. An improperly installed grounding system can present a shock hazard to personnel. Connect any power panel(s) ground buses and transformers XO bond that are in close proximity to the computer equipment to the site grounding grid. Methods of achieving a sufficiently high-frequency ground grid are described in the next sections. Raised Floor "High-Frequency Noise" Grounding If you use a raised floor system, install a complete SRG to maintain equal potential over a broad band of frequencies. Connect the grid to the equipment cabinet and electrical service entrance ground at multiple connection points by using a minimum #6 AWG (16 mm) wire ground conductor. Figure 1-1 (page 15) illustrates a metallic strip grounding system. IMPORTANT: Regardless of the grounding connection method used, you must ground the raised floor as an absolute safety minimum. HP recommends the following approaches to create an effective and safe 2-foot by 2-foot signal reference grid: • 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-resistant 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. The structure needs to be mechanically bonded to a known good ground point. • Better-Add a grounded #6 AWG (16mm) minimum copper wire grid mechanically clamped to floor pedestals and properly bonded to the building or site ground. • Best-Add a grounding grid to the subfloor. Build the grounding grid with copper strips mounted to the subfloor. Use strips that are 0.032 inches (0.08 cm) thick and a minimum of 3.0 inches (8.0 cm) wide. Connect each pedestal to four (4) strips using 1/4-inch (6.0-mm) bolts tightened to the manufacturer's torque specification. 14 General Site Preparation Guidelines

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Dual Power Source Grounding
The use of dual power might create an electrical potential that can be hazardous to personnel
and might cause performance issues for the equipment. When using dual power sources, measure
voltage potentials with a high impedance digital multi-meter (DMM).
Dual power sources might originate from two different transformers or two different UPS devices.
Measure voltage potentials from ground pin to ground pin of these sources and verify them to
be at or near 0.0 V. Investigate voltage levels that measure above 3.0 V because increased voltages
can be hazardous to personnel.
Cabinet Performance Grounding (High-Frequency Intercabinet Ground)
Some safety power distribution wires are too long and too inductive to provide adequate
high-frequency return paths. For sufficient protection, signal interconnects between system
cabinets might need high-frequency ground return paths
in addition to
the safety or power
distribution system 50–60Hz grounding system. HP recommends the use of a properly installed
signal reference grid (SRG) also bonded to the 50–60Hz grounding system.
WARNING!
Do not use cabinet-to-floor ground straps in place of a properly installed safety
(50–60Hz) grounding system, nor in place of a properly installed Signal Reference Grid. An
improperly installed grounding system can present a shock hazard to personnel.
Connect any power panel(s) ground buses and transformers XO bond that are in close proximity
to the computer equipment to the site grounding grid. Methods of achieving a sufficiently
high-frequency ground grid are described in the next sections.
Raised Floor “High-Frequency Noise” Grounding
If you use a raised floor system, install a complete SRG to maintain equal potential over a broad
band of frequencies. Connect the grid to the equipment cabinet and electrical service entrance
ground at multiple connection points by using a minimum #6 AWG (16 mm) wire ground
conductor.
Figure 1-1 (page 15)
illustrates a metallic strip grounding system.
IMPORTANT:
Regardless of the grounding connection method used, you must ground the
raised floor as an absolute safety minimum.
HP recommends the following approaches to create an effective and safe 2-foot by 2-foot signal
reference grid:
•
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-resistant 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. The structure needs to be mechanically bonded to a known good ground point.
•
Better—Add a grounded #6 AWG (16mm) minimum copper wire grid mechanically clamped
to floor pedestals and properly bonded to the building or site ground.
•
Best—Add a grounding grid to the subfloor. Build the grounding grid with copper strips
mounted to the subfloor. Use strips that are 0.032 inches (0.08 cm) thick and a minimum of
3.0 inches (8.0 cm) wide.
Connect each pedestal to four (4) strips using 1/4-inch (6.0-mm) bolts tightened to the
manufacturer’s torque specification.
14
General Site Preparation Guidelines