The Earthing and Bonding System

Earthing and Bonding System of the Data Center Room

What is SRG?
SRG (Signal Reference Grid) is essentially a high-frequency, low-impedance reference network that provides a common ground reference for all equipment within a specific area. By creating an equipotential grounding surface, SRG serves as a reference system for a wide frequency range—from DC up to the megahertz range—making it a reliable grounding reference for IT equipment.

By creating a low-impedance reference grid, SRG limits or eliminates potential differences between data systems and other systems during transient overvoltages or power disturbances. The primary objectives of implementing an SRG system include reducing or eliminating electrical noise, minimizing potential differences between data systems and other systems during transient overvoltages, limiting power system disturbances, and suppressing external noise.

The SRG system consists of a network of copper conductors installed in data centers, typically beneath the raised floor. SRG may also be constructed using copper strips, aluminum conductors, raised floor substructures, or, in specific cases, rigid metal sheet coverings.

It is important to note that at high frequencies, flat strip conductors exhibit lower inductive reactance compared to standard round conductors—meaning they have lower impedance at high frequencies. This characteristic makes the SRG system inherently low-impedance. Therefore, the use of flat conductors (copper strips) is strongly recommended for implementing an SRG system.

The figure below, taken from IEEE 1100 standard, compares the impedance of an SRG system with that of a single-point grounding system:

SRG Since 1983, following the publication of the U.S. Federal Information Processing Standard (FIPS PUB 94) titled “Guideline on Electrical Power for ADP Installations”, SRG has become a standard component in data center design. This standard first established the scientific principles of electrical interference with IT equipment and then introduced design strategies to mitigate these interferences, providing practical solutions to the problem.

The primary objective of SRG is to reduce unwanted noise voltages in copper communication channels that are ground-referenced. Among the voltages controlled by SRG are variations in ground potential between different IT devices.

According to a U.S. Air Force technical engineering report, SRG systems have also been used to control electrostatic discharge (ESD). By providing a conductive equipotential reference plane, SRG helps high-frequency signals to be referenced properly, thereby minimizing interference and noise.

Given the high cost of implementing SRG systems, their design and installation in data centers must comply with standards such as TIA-607.B, TIA-942, BICSI-002-2011, IEEE 1100, FIPS PUB 94, and IEC 62305 to ensure proper operation and system reliability.

For example, the SRG mesh size can range from 60 cm up to 3 m, but according to standards, the ideal mesh size—especially for high-frequency performance—is 60 cm × 60 cm.

After the SRG grid is installed, it must be bonded to the raised floor pedestals. If the SRG is implemented using flat copper strips with a 60 × 60 cm mesh, then at least one bonding connection is required for every six pedestals. If the SRG is implemented with round conductors, at least one bonding connection is required for every three pedestals. It is also critical that the bonding conductor length between the raised floor pedestal and the SRG grid does not exceed 60 cm.