Resistance per metre value for 25mm meter tails?

From Table I1 of the OSG, or the equivalent table in GN3, or BS 60228, the DC resistance at 20 ºC is 0.727 mΩ/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 mΩ (equivalent to around 14 m of 25 mm² conductor at 20 ºC).

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 Ω (100 mΩ) in  cases where the expected reading is well below this value - it's the resolution and accuracy of the test instrument.

From Table I1 of the OSG, or the equivalent table in GN3, or BS 60228, the DC resistance at 20 ºC is 0.727 mΩ/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 mΩ (equivalent to around 14 m of 25 mm² conductor at 20 ºC).

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 Ω (100 mΩ) in  cases where the expected reading is well below this value - it's the resolution and accuracy of the test instrument.