Let's look at this from a different poit of view....
Any imbalance, caused by the differing resistances of the wires, will be expressed in heat.
I suppose that resistance measurements could be taken- but there is still the mattter of tolerances.
One thing that does not change is the temperature rating of the terminations. I suppose it could be argued that if the circuit can run three hours at full load, without exceeding 75 degrees C at the terminations, you're 'within tolerance.'
