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The realities of trying to test in occupied domestic properties
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<blockquote data-quote="SPECIAL LOCATION" data-source="post: 508495" data-attributes="member: 250"><p>You don't need an App, Table 11, pg 196 gives the resistance values for single conductors and T&amp;E.. </p><p></p><p>just do a bit of basic maths...</p><p></p><p>For a single conductors</p><p></p><p>1.0mm is 18.1 miliohm/meter, or 0.181 ohm per 10m, or 1.81ohm per 100m</p><p></p><p>1.5mm is 12.1 miliohm/meter, or 0.121 ohm per 10m, or 1.21ohm per 100m</p><p></p><p>You can calculate the ratio difference between conductors, </p><p></p><p>so a 1.5mm is 0.668x a 1.0mm value.. (0.181 x 0.668) = 0.121</p><p></p><p>So if R2 was 1.0mm &amp; R1 was 1.5mm, the R1 value will be 0.668 x your measured R2.</p><p></p><p>e.g. if you had measured R2 as 0.55ohm..</p><p></p><p>If both R1 &amp; R2 were the same physical size R1+R2 would simply be double your measured value.. 1.1ohms</p><p></p><p>But if it was 1.5/1.0mm T&amp;E R1 will be 0.55x0.668 = 0.36</p><p></p><p>So R1+R2 would be 0.36+0.55 = 0.91</p><p></p><p>I often also use rough values per 10m to suss out if my test readings equate to expected values for the physical size of the circuits/building..</p><p></p><p>i.e. for our 0.55 reading...</p><p></p><p>If it was a 1.0mm CPC it would be approx 30m (0.55/0.181)x10.</p><p></p><p>If it was a 1.5mm CPC it would be approx 45m (0.55/0.121)x10.</p><p></p><p>Which can give some idea if your rough guesstimates of cable size are reasonable or not?</p><p></p><p>On a similar note, I was investigating a high resistance ring fault on a socket circuit once,</p><p></p><p>and had to explain to a customer although the sockets were working,</p><p></p><p>the readings suggested there was just over half a kilometre of cable between the bedroom and lounge below it!!</p><p></p><p>which needed further investigation for concealed junction boxes, cable damage etc.. </p><p></p><p> Guinness</p></blockquote><p></p>
[QUOTE="SPECIAL LOCATION, post: 508495, member: 250"] You don't need an App, Table 11, pg 196 gives the resistance values for single conductors and T&E.. just do a bit of basic maths... For a single conductors 1.0mm is 18.1 miliohm/meter, or 0.181 ohm per 10m, or 1.81ohm per 100m 1.5mm is 12.1 miliohm/meter, or 0.121 ohm per 10m, or 1.21ohm per 100m You can calculate the ratio difference between conductors, so a 1.5mm is 0.668x a 1.0mm value.. (0.181 x 0.668) = 0.121 So if R2 was 1.0mm & R1 was 1.5mm, the R1 value will be 0.668 x your measured R2. e.g. if you had measured R2 as 0.55ohm.. If both R1 & R2 were the same physical size R1+R2 would simply be double your measured value.. 1.1ohms But if it was 1.5/1.0mm T&E R1 will be 0.55x0.668 = 0.36 So R1+R2 would be 0.36+0.55 = 0.91 I often also use rough values per 10m to suss out if my test readings equate to expected values for the physical size of the circuits/building.. i.e. for our 0.55 reading... If it was a 1.0mm CPC it would be approx 30m (0.55/0.181)x10. If it was a 1.5mm CPC it would be approx 45m (0.55/0.121)x10. Which can give some idea if your rough guesstimates of cable size are reasonable or not? On a similar note, I was investigating a high resistance ring fault on a socket circuit once, and had to explain to a customer although the sockets were working, the readings suggested there was just over half a kilometre of cable between the bedroom and lounge below it!! which needed further investigation for concealed junction boxes, cable damage etc.. Guinness [/QUOTE]
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