Grounding Systems

Power Distribution Safety Grounding

The power distribution safety grounding system consists of connecting various points in the power distribution system to earth ground using green (green/yellow) wire ground conductors. Having these ground connections tied to metal chassis parts that may be touched by computer room personnel protects them against shock hazard from current leakage and fault conditions.

Power distribution systems consist of several parts. Hewlett-Packard recommends that these parts be solidly interconnected to provide an equipotential ground to all points.

Main Building Electrical Ground

The main electrical service entrance equipment should have an earth ground connection, as required by applicable codes. Connections such as a grounding rod, building steel, or a conductive type service pipe provide an earth ground.

Electrical Conduit Ground

All electrical conduits should be made of rigid metallic conduit that is securely connected together or bonded to panels and electrical boxes, so as to provide a continuous grounding system.

Power Panel Ground

Each power panel should be grounded to the electrical service entrance with green (green/yellow) wire ground conductors. The green (green/yellow) wire ground conductors should be sized per applicable codes (based on circuit over current device ratings).

	NOTE: The green wire ground conductor mentioned above might be a black wire marked with green tape.

Computer Safety Ground

	WARNING! When dual power sources are used, always measure voltage potentials. Failure to do so can result in exposure of personnel to electric shock hazard and damage to the equipment.

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 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. Figure 2-1 “Raised Floor Metal Strip Ground System” 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.

Hewlett-Packard recommends the following approaches:

Figure 2-1 Raised Floor Metal Strip Ground System

Equipment Grounding Implementation Details

Connect all Hewlett-Packard equipment cabinets to the site ground grid as follows: