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Resistance per metre value for 25mm meter tails?

whjohnson

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

Parents
  • 0

    Too low to measure with reasonable accuracy with a standard instrument,

    A special low ohms meter will be needed, presumably with a Kelvin connection.

    Alternatively pass a significant current through the cable and measure the voltage drop. 

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  • 0

    Too low to measure with reasonable accuracy with a standard instrument,

    A special low ohms meter will be needed, presumably with a Kelvin connection.

    Alternatively pass a significant current through the cable and measure the voltage drop. 

Children
  • 0 in reply to broadgage

    Agree, at quite a bit less than 1 milliohm per metre per tail, unless it is a very long roll you will struggle to get an accurate answer with  simple 2 probe metering as contact resistances can easily be tens of milliohms and then dominate the answer giving an error of tens of metres.

    However, an ammeter, a volt meter and a suitable load, perhaps like the workshop kettle, may be a good way to demonstrate the effect.

    Generally for any odd cross-section, to estimate resistance, copper can be taken as 16 to 19 milliohms per metre length per mm cross section. That is  to say take 16 milliohms, multiply by the there and back distance (assuming that is a pair of wires being measured with a short at the far end) and divide by the cross section in mm2.,
    The 16 milliohm figure is almost always too low, and assumes cold conductors of very pure copper, and is good for worst case PSSC estimates The 19m ohm is more likely to be correct for cables in use. If you have it, maker's data is best.
    Mike

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