Raised floors

Learn how a raised floor environment improves data center operational efficiency.

A raised floor accomplishes the following major objectives:

• Improves operational efficiency and allows greater flexibility in the arrangement of equipment
• Permits the space between the two floors to be used to supply cooling air to the equipment or area
• Allows for future layout change with minimum reconstruction cost
• Protects the interconnecting cables and power receptacles
• Prevents tripping hazards

A raised floor should be constructed of fire-resistant or noncombustible material. The two general floor types are shown in the following figure. The first figure is of a stringerless floor, and the second figure is a floor with stringers.

Figure 1. Raised floors types

Raised floor factors:

• No metal or highly-conductive material that might be at ground potential should be exposed to the walking surface when a metallic raised-floor structure is used. Such exposure is considered an electrical safety hazard.
• The raised-floor height should be between 155 mm (6 in.) and 750 mm (30 in.). For processors with multiple channels, a minimum raised-floor height of 305 mm (12 in.) is recommended. Clearance must be adequate to accommodate interconnecting cables, fiber cable raceways, power distribution, and any piping that is present under the floor. Experience has shown that higher raised-floor heights allow better air-conditioning balance in the room.
• Caster point loads on some servers can be as high as 455 kg (1,000 lb.) concentrated load anywhere on the panel with a 2 mm (0.080 in.) maximum deflection .
• When a raised-floor panel is cut for cable entry or air supply, an additional panel support (pedestal) might be required to restore the structural integrity of the panel to the above requirement.
• Use protective covering (such as plywood, tempered masonite, or plyron panels) to prevent damage to floor tiles, carpeting, and panels while equipment is being moved into or is relocated within the installation. When the equipment is moved, the dynamic load on the casters is significantly greater than when the equipment is stationary.
• Concrete subfloors require treatment to prevent the release of dust.
• Use noncombustible protective molding to eliminate sharp edges on all floor cutouts to prevent damage to cables and hoses and to prevent casters from rolling into the floor cutout.
• Pedestals must be firmly attached to the structural (concrete) floor using an adhesive.
• Cable cutout size information is determined by the volume of cables passing through the cutout. See the server's documentation for recommendations on the cable cutout size.

Signal reference ground

To minimize the effects of high-frequency (HF) interference and other undesired electrical signals (commonly referred to as electrical noise), a Signal Reference System (SRS) may be recommended. An SRS may be made up of a Signal Reference Ground or Grid (SRG), or a Signal Reference Plane (SRP). A Signal Reference Ground or Grid may also be known as a Zero Signal Reference Ground (ZSRG). Regardless of the name used, the intent is to provide an equal potential point of reference for equipment installed in a contiguous area for a wide range of frequencies. This is accomplished by installing a network of low impedance conductors throughout the information technology room.

Access (raised) flooring systems that utilize bolted stringer construction can be used to provide a simple SRG. Floor systems that have either no stringer or snap-in stringers do not provide for an effective SRG, and other methods for installing a SRG should be used.

For safety requirements, the SRG must be connected to earth ground. SRG practices recommend that all metallic objects that cross the SRG area are to be bonded (mechanically connected) to the SRG.

For more information on Signal Reference Grounds, contact your IBM® Installation Planning Representative.

Figure 2. Signal reference ground