Resistance per metre value for 25mm meter tails?

Question

what is the resistance per metre value for 25mm meter tails? I have 2 rolls of old colour meter tails and would like to work out how many meteres there are on each roll without physically unrolling and measuring with a tape! A simple end to end measurement with a ohm meter would be much quicker. 
 many thanks in advance

gkenyon · Answer

From Table I1 of the OSG, or the equivalent table in GN3, or BS 60228, the DC resistance at 20 &ordm;C is 0.727 m&Omega;/m. 
 whjohnson said: A simple end to end measurement with a ohm meter would be much quicker. 
 Quicker, yes, but not at all anywhere near accurate enough for even a basic idea, unless either you have well over 100 m on the reel, or unless the instrument used is a 4-wire micro-ohm meter ( 'kelvin' type, sometimes called a 'ductor tester' by those who use such instruments to check high current terminations at, or within, switchboards and transformers). The reason is that the contact resistance of a 2-wire instrument can be in excess of 10 m&Omega; (equivalent to around 14 m of 25 mm 2 conductor at 20 &ordm;C). With the resolution and accuracy of a standard continuity tester used for electrical installations, you might need to add on another "uncertainty" of perhaps another 14 m or even more. 
 As an aside, this is the reason why tests for "bonding" in GN 3, and tests for most appliance product standards, and PAT testing, have a "pass" limit of 0.1 &Omega; (100 m&Omega;) in cases where the expected reading is well below this value - it's the resolution and accuracy of the test instrument.

Resistance per metre value for 25mm meter tails?

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