Grounding Products and Systems - Elec.ru

Equipotential BondingSignal Reference Grid (SRG)The Signal Reference Grid (SRG) is a pre-fabricated low impedancenetwork of conductors established to create an equipotential plane forhigh frequency, low voltage digital signals in such applications as intensivecomputer, telemetry and telecommunications installations.Digital signal line voltages are typically low. Their sensitivity to transientnoise is very high (typically 1 volt for some digital systems). The SRGcomplies with IEEE Standard 1100-1992 for grounding practices insensitive electronic environments.Proper grounding and bonding of sensitive electronic systems, includingcomputer installations, requires careful consideration of all frequenciesfrom DC to over 100 megahertz. The local requirements for electrical faultcurrent and lightning protection must also be met.Signal Reference Grid (SRG)The safety grounding system required by Code does not address thespecial requirements of noise immunity. An additional "grounding" systemcalled the Signal Reference Grid (SRG) is needed to assure trouble-freeequipment performance.(See Technical Section on page 73)The importance of SRGs for Computer ApplicationsIn order to minimize the effects of noise, many computer manufacturers,users and government agencies have detailed specifications regardingcomputer grounding. Computer installations are particularly sensitive to:• Coupling between adjacent power, data circuits and ground,where noise can be introduced into cables – even nearby lightningstrikes can be a real threat•Noise levels from nearby transmitters may be a serious problem andrequire shieldingFigure 40. Pre-fabricated Signal reference Grid installed under computer room floor.Components of the SRGAn effective SRG:• Uses a multitude of conductors to create a very lowimpedance to noise at any frequency• Typically uses two foot spacing between conductors• Uses terminations that provide a constant impedanceover the life of the facility• Uses multiple paths within the SRG to allow the noisecurrents to divide at each crossover, which furtherreduces voltage drop• Uses a mesh made of flat copper strips to provide themost functional low impedance and cost effectivecomputer grounding system available.• Uses welded connections to assure a noise-free bondWelded Connections®Welded connections are often specified because they are the onlyconnections proven to assure a "noise-free" bond. Normal shockand vibration jar mechanical connections, creating electronic noise.This causes relatively high Ldi/dt voltages due to a sudden changein connection impedance. This sudden change can result in pulseswhich can be coupled onto the signal circuits. These unwantedsignals can create false data or even cause permanent circuitdamage. Corrosion, dirt and cleaning fluids cannot interfere withthe molecular bond of a welded joint.Figure 39. Signal Reference Grid with bonded connections to main building ground.Ph: 1-800-677-9089www.erico.com43