RBJ Commentary to AFCI problems, One of the most common problems with running multiple wiring in any type raceway is that single conductor circuits run physically together with low magnetic cancelling for the BC being used. This can cause circuit coupling anomalies. NM paired conductors has one of the main advantages between conduit versus cable run environments. Regardless, circuit twist ratios are used to decrease coupling between cables. This could be one reason why the 2014 NEC is restricting 14 and 12 AWG runs at 50 and 70 ft lengths. Unfortunately, the NEC and AFCI MANUFACTURERS are not resolving the coupling problems due to high current load circuits being bundled together in the BC home runs. As a communication satellite circuit harness designer in an earlier career, relating to a residential rope monkey, this is one reason why all bus and telemetry circuits have isolated harnesses and each have their signal intrinsic return circuits twisted together. Telecom has the same condition to correct when installing and isolating signal and power circuits. (Data cable CAT-6 use four pair each having a varied twist ratio to basically inhibit coupling or cross-talk.) Contractors could have a better understanding with the electronic industry complexities (AFCI) and become involved in running better wire routing and termination methods. Parallel pigtail circuit usage, tight pre-twist connection bonds, no neutral sharing, no loops, and better selection of how multiple wire paired run lengths are spaced based on current draw and fault interrupter protection assembly in a system. R. Benton Jacks July 17, 2013