Introduction to Data Centre Design

Introduction to

Data Centre Design

Barry Elliott

Earthing,

grounding and

bonding

Earthing – what’s the point

• Safety from electrical hazards

• Reliable signal reference within the entire

information technology installation

• Satisfactory electromagnetic performance of

the entire information technology installation

Applicable Standards

•UK

•BS 6701 Telecommunication cabling and equipment installations

•BS 7671 Requirements for electrical installations: IEE wiring

regulations 16th _Edition

•Europe

•EN 50310 Application of equipotential bonding and earthing in buildings with information technology equipment

•EN 50174-2 Information technology – Cabling installation – Part 2 – installation and planning practices inside buildings

Applicable Standards

• World

• IEC 60364-1

Electrical installations of buildings, various sections

including; Part 5-548: Earthing arrangements and equipotential

bonding for information technology equipment

• ISO 11801:2002

Information technology – cabling for customer

premises

• USA

• ANSI/TIA/EIA-J-STD-607

Commercial building grounding and

bonding requirements for telecommunications

• IEEE STD 1100-2005

Powering and Grounding Sensitive

Electronic Equipment

Applicable Standards –

and………….

• ETS 300 253

Equipment engineering – earthing and

bonding of telecommunications equipment in

telecommunication centres

• ITU-T K.27

Bonding configurations and earthing inside a

telecommunications building

• ITU-T K.31

Bonding configurations and earthing of

telecommunications installations inside a subscriber’s

building

Terminology

•Earthing

•The connection of the exposed conductive parts of an

installation to the main earthing terminal of that

installation (BS 7671)

•Equipotential bonding

•The electrical connection putting various exposed

conductive parts and extraneous conductive parts at a

substantially equal potential (EN 50174-2)

•Grounding (American)

•A conducting connection, whether intentional or

accidental, between an electrical circuit and the earth.

(TIA/EIA-607)

Bolting it all together – the

equipotential bonding system

• In an installation, main equipotential bonding conductors shall

connect to the main earthing terminal extraneous conductive parts of that installation including the following:

• Water service pipes • Gas service pipes

• Other service pipes and ducting

• Central heating and air conditioning systems • Exposed metallic structural parts of the building • The lightning protective system

Main earthing terminal Earthing conductor Exposed conductive parts Circuit protective conductors Supplementary equipotential bonding conductors (where required)

Extraneous conductive part

Main equipotential bonding conductors

Main metallic water pipe

EN 50310

Application of equipotential

bonding and earthing in buildings with information technology

EN 50310

The frame ground grid shall be installed with a maximum cell size of 2 metres in each horizontal direction. The minimum cross-sectional area of the conductors that create the frame ground grid shall be 10 mm² min. The frame ground grid shall be connected to the earthing network at multiple points, where available.

If the raised floor is installed with a surface that is intended to provide protection against electrostatic discharge, the DC resistance between the raised floor surface and the

6.3 mm thick 101 mm high

Earth

Earth

Additionally, every sixth metallic raised floor

pedestal needs to be

bonded (to the SRG). This helps to bleed off static charges built up from the raised floor system.

*EN 50174-2 suggest every 2 or 3 pedestals earthed with a 10 sq mm wire

Underfloor TGB

serving a row of

racks

Signal reference grid

•

• IEEE Standard 1100 provides

recommendations for the electrical design of bonding and grounding. Consideration should

be given to installing a common bonding network (CBN) such as a signal reference

structure as described in IEEE Standard 1100 for the bonding of telecommunications and computer equipment.

• • If the system is on raised flooring, use a 2-foot x 2-2-foot (61-cm x 61-cm) grounding grid.

SRG - Do we need one?

• 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 an

SRG should be used. (IBM)

• …system reference potential plane (SRPP) conductive solid plane, as an ideal goal in potential equalising, is approached in practice by horizontal or vertical meshes. The mesh width thereof is adapted to the frequency range to be considered. Horizontal

• The high operating frequencies of modern computer

equipment

require

that computer room products be

supported both by a good equipment-grounding

system and an effective signal reference grid.

Compaq/HP

• A signal reference grid

should

be designed for the

computer room. This provides an equal potential

plane of reference over a broad band of frequencies

through the use of a network of low-impedance

ETSI EN 300 253

• 4.2 Signal reference

• Reliable signal reference shall be provided by a SRPP dedicated at

least to a functional unit or a system block. To avoid undue functional distortion or risk of component failure, the SRPP shall provide

sufficiently low impedance up to the highest frequency to be regarded by using a metal plane or a meshed configuration having adequate mesh dimensions, e.g. a bonding mat. The frequency band to be

covered shall include the spectral components of transients caused by switching, short circuits and atmospheric discharges.

• Critical equipment should be located and bonded to the SRG at more than 6 feet away from the building steel or other potential lightning paths.

• All interconnecting communications, data and power cables should lay on or very close to the SRG

• Bond the signal reference grid to each piece of electronic

equipment and to any other electrical or mechanical equipment located on the signal reference grid.

• Bonding connections to the signal reference grid should be as short as practical with no sharp folds or bends. Flexible straps are preferred to the use of round conductors.