Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, about an earthing system in an existing three-phase plus neutral supply, is answered by SELECT:
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Question: How can we implement an earthing system in an existing three-phase plus neutral electrical supply for the operation of RCDs - so as to provide basic protection? Answer: I presume when you use the term 'basic' protection, you are not referring to the defined term in BS7671:2008 - Basic protection (formerly referred to as protection against direct contact) is protection against electric shock under fault free conditions and usually comprises insulation of live parts and enclosure behind barriers.
Fault protection (which I think you are actually referring to) is protection against electric shock under single fault conditions
To protect against fault currents, the most common method used is automatic disconnection of supply (ADS), which requires connection to a recognised earthing system - such as a TN-S system, TN-C-S system or TT system on a public supply. An ADS system relies on protective earthing, protective equipotential bonding and automatic disconnection of the supply protective device in the event of a fault occurring.
In this instance, to obtain connection to recognised earthing system, you could either:
1) Contact the local supply authority within your area who may be able to provide connection to a TN-S system or more likely a TN-C-S system.
2) If the the distributor cannot, for some reason, provide connection to one of the above earthing systems, the installation can be provided with its own earth electrode as the means of protective earthing. This would be classified as a TT earthing system.
To see many more Q & A in Voltimum UK's Experts Area, please click on the link: www.voltimum.co.uk/consult.php?universe=consult.index.questions
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