Experience has shown that dc power arrangements are often given insufficient consideration by traditional building services installation designers, when it comes to earthing and bonding of telecommunications facilities. This paper aims to raise awareness and focuses on dc system configurations, dynamics, performance (e.g. functional earthing) and electrical safety considerations (e.g. protective earthing). Unlike traditional ac powered building services where the building earthing system is considered passive under normal conditions (e.g. non-conductive part of the ac power distribution architecture), the telecommunications building earthing infrastructure is used as part of the dc return path and plays a critical role in meeting dc power systems safety, performance and reliability requirements. This paper starts by providing a brief overview of a typical dc power system installation, highlighting key safety and performance features relating to earthing. It then discusses the general requirements for telecoms equipment area earthing and the key considerations for dc power systems. Finally a case study is outlined to illustrate the author's experiences in the design, development and implementation of a dc power distribution and earthing arrangement for System X switch sites.
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