[ Update: Technical ]
Earthing of raised access floor systems
ECA head of Technical Services Giuliano Digilio updates members with his latest guidance note
O
ver the years, there have been many differences of opinion between specifiers, designers, contractors and end user clients regarding whether or not raised access floor
systems need to be earthed. Following recent industry discussions, this guidance note goes some way to try to promote a common agreement. The IET Wiring Regulations (BS 7671) The
Requirements for Electrical Installations, the Code of Practice for Protective Earthing of Electrical Installations (BS 7430), and the IET Guidance Notes, and so on, do not require raised access flooring systems in general office areas to be earthed, as these floor systems are not considered as exposed or extraneous conductive parts under its normal conditions of use. In practice, unless there are very exceptional circumstances, or where functional requirements need to be taken into account by the electrical design engineer and considered in the designer’s risk assessment for the electrical installation, the conductive parts of a raised
access floor system will be neither exposed-conductive- parts nor extraneous-conductive-parts. If functional requirements are considered necessary by the person responsible for the project electrical installation design – for example, computer server rooms, data centres, and other telecommunications-type installations or similar – then account of such requirements should be detailed within the respective electrical services project design information and the electrical specification by the project design engineer. For further information regarding such specialist requirements, these can be found in BS EN 50310:2010 Application of Equipotential Bonding and Earthing in Buildings with Information Technology Equipment.
Conducting The electrical or mechanical equipment that is normally fixed within typical office area raised access floor systems, such as electrical service floor outlet boxes for LV socket- outlets and ICT outlets or air conditioning equipment and units, will normally either be of Class I or Class II-type construction. The exposed-conductive-parts of Class I equipment are required to be connected to earth by a circuit protective conductor designed to conduct the likely earth fault current. Class II equipment is designed such that any insulation fault in this equipment cannot result in a fault current being passed on to any other conductive parts with which the equipment may be in contact. The conductive parts of a raised access floor incorporating Class I or Class II equipment are not intended to conduct earth fault current, and so such parts need not be intentionally earthed. While some conductive parts of the raised access floor systems may be earthed by virtue of being in contact with exposed- conductive-parts, there is no need to make a deliberate earth connection.
Conclusion In conclusion, unless there are functional requirements or exceptional circumstances, the conductive parts of raised access floor systems will not introduce a potential that does not already exist in the space in which the floor is installed. In normal circumstances, therefore, there is no need to arrange for the conductive parts of the floor system to be connected to either a main protective bonding conductor or to any supplementary protective bonding conductor for electrical safety reasons.
September 2012 ECA Today 61
KINGSPAN ACCESS FLOORS
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