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Student & Learning Zone - City & Guilds
Earth electrode testing
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<blockquote data-quote="SPECIAL LOCATION" data-source="post: 501904" data-attributes="member: 250"><p>What you are thinking of is the test shown on Pg 113 of the current OSG.. "Earth Electrode Test"....</p><p></p><p>i.e. establishing the resistance to earth of the rod itself (Ra).</p><p></p><p>What you boss was doing, as you quite rightly state, was an External earth loop test..</p><p></p><p>i.e. The local rod and the suppliers earth..</p><p></p><p>Which by definition the Ze must be greater than the Ra as Ze on a TT includes your Ra + Suppliers earth electrode..</p><p></p><p>(Suppliers earth is stated as max 21ohms) </p><p></p><p>So providing the Ze is value is acceptable, (lower than 200 and nearer to 21 as possible)..</p><p></p><p>There isn't much need to measure Ra itself.</p><p></p><p>See note on bottom of page 11 and top of page 12 OSG..</p><p></p><p>These are all based on the 411.5 section of the big book!</p><p></p><p>Basically in the real world time is money... </p><p></p><p>doing an Ra takes longer than a quick Ze test!</p><p></p><p>If there were concerns about the ground conditions then further investigation by doing proper Ra test may be beneficial..</p><p></p><p>Or may be just bang another (or deeper) rod in!!</p><p></p><p> Guinness</p></blockquote><p></p>
[QUOTE="SPECIAL LOCATION, post: 501904, member: 250"] What you are thinking of is the test shown on Pg 113 of the current OSG.. "Earth Electrode Test".... i.e. establishing the resistance to earth of the rod itself (Ra). What you boss was doing, as you quite rightly state, was an External earth loop test.. i.e. The local rod and the suppliers earth.. Which by definition the Ze must be greater than the Ra as Ze on a TT includes your Ra + Suppliers earth electrode.. (Suppliers earth is stated as max 21ohms) So providing the Ze is value is acceptable, (lower than 200 and nearer to 21 as possible).. There isn't much need to measure Ra itself. See note on bottom of page 11 and top of page 12 OSG.. These are all based on the 411.5 section of the big book! Basically in the real world time is money... doing an Ra takes longer than a quick Ze test! If there were concerns about the ground conditions then further investigation by doing proper Ra test may be beneficial.. Or may be just bang another (or deeper) rod in!! Guinness [/QUOTE]
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Earth electrode testing
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