Re: Parrallel
Your concept of measuring one current and calculating the impact of a higher current is perfectly valid. Regrettably, it would prove to be of no real value. Again, it boils down to circular reasoning.
Presuming your overcurrent device is set at the combined ampacity of your set of parallel cables, and presuming that the cables are of ?slightly? different lengths, then when you calculate the current through each of the cables (based on your earlier measurements at a lower current), your result will be that one cable has less than the 310.16 limit going through it, and the other will have more than the 310.16 limit going through it. You can calculate how much more than the limit, and then ask whether that will be a significant amount. But that takes you back to your original question, ?At what point does it REALLY cause a concern??
The bottom line is that, however you measure, calculate, or otherwise infer the amount of difference between the two cables, the question of ?Is that a significant difference?? will still remain open to debate. The code does not say ?within 5% of the same length,? nor does it provide any other guidance to the installer or to the inspector.