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Functional/clean earthing guidance required

E95

Is anyone able to provide some guidance to us on the topic of "clean" earthing?

We're currently discussing the requirements for clean earthing, after reading through BS 7671:2018+A2 and BS 50310, none of which seem to provide a clear definition of what this is

Essentially a scope requests that a "clean" earthing supply is requested to a data installation, however the MET is not within the same building and may require some fairly extensive works to bring a conductor over from the MET in a separate building.

Is this necessary, or, can it be taken from an "Earthing marshalling terminal" from within a Sub-distribution board and still meet the "clean earth" definition?

 

  • Section 10.1 of GN8 states "The MET or bar of the computer system installation is connected directly to the building Main Earth Terminal (MET) by a protective conductor"
  • Section 2.7 of GN1 states "The main earthing terminal or bar of the computer system is connected directly to the main earthing terminal by a protective conductor"
  • MET is defined as "The terminal or bar provided for the connection of protective conductors, including protective bonding conductors, and conductors of functional earthing, if any, to the means of earthing", GN8 also refers to any subsequent downstream earthing terminals of downstream distribution boards as "Earthing marshalling terminal" and not an MET.
  • BS 50310 Telecommunications bonding networks for buildings and other structures doesn't (to me) seem to define what a "clean" or a "functional" earth system is and I can't make heads or tails of the standard
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    Changes in terminology and wording and interpretation again!

    I do remember as a young apprentice in the very early 80's and one of the best electrical lecturers I ever had litterly "Bounced" the blackboard duster ( NO Smart boards in those days) off a apprentice who misinterpretated what the lecturer was saying about earthing. His quote was "Son, you can call it whatever the hell you want, but when you fall on your backside ( He used another word!!) all earth is DIRTY!!!!!!" At the time rest of us were a little bit frightened to ask any more questions but as my knowledge and career grew, there was a lot of truth in that statement. 

    Cheers GTB

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  • 0

    Changes in terminology and wording and interpretation again!

    I do remember as a young apprentice in the very early 80's and one of the best electrical lecturers I ever had litterly "Bounced" the blackboard duster ( NO Smart boards in those days) off a apprentice who misinterpretated what the lecturer was saying about earthing. His quote was "Son, you can call it whatever the hell you want, but when you fall on your backside ( He used another word!!) all earth is DIRTY!!!!!!" At the time rest of us were a little bit frightened to ask any more questions but as my knowledge and career grew, there was a lot of truth in that statement. 

    Cheers GTB

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