Static electricity and floor resistance

Use these guidelines to minimize static electricity buildup in your data center.

Floor covering material can contribute to buildup of high static electrical charges as a result of the motion of people, carts, and furniture in contact with the floor material. Abrupt discharge of the static charges causes discomfort to personnel and might cause malfunction of electronic equipment.

Static buildup and discharge can be minimized by:

• Maintaining the relative humidity of the room within the server operating limits. Choose a control point that normally keeps the humidity between 35 percent and 60 percent. See the Air conditioning determination for further guidance.
• Providing a conductive path to ground from a metallic raised floor structure including the metal panels.
• Grounding the raised floor metallic support structure (stringer, pedestals) to building steel at several places within the room. The number of ground points is based on the size of the room. The larger the room, the more ground points are required.
• Ensuring the maximum resistance for the flooring system is 2 x 10¹⁰ ohms, measured between the floor surface and the building (or an applicable ground reference). Flooring material with a lower resistance will further decrease static buildup and discharge. For safety, the floor covering and flooring system should provide a resistance of no less than 150 kilohms when measured between any two points on the floor space 1 m (3 ft) apart.
• Maintenance of antistatic floor coverings (carpet and tile) should be in agreement with the individual supplier's recommendations. Carpeted floor coverings must meet electrical conductivity requirements. Use only antistatic materials with low-propensity ratings.
• Using ESD-resistant furniture with conductive casters to prevent static buildup.

Measuring floor resistance

The following equipment is required for measuring floor resistance:

• A test instrument similar to an AEMC-1000 megohmmeter is required for measuring floor conductivity.

The following figure shows the typical test connection to measure floor conductivity.

Figure 1. Typical test connection to measure floor conductivity