I think it fair to say that it is common knowledge amongst sparks to direct all live conductors and associated protective conductor through a common aperture in a ferromagnetic enclosure. So I want to direct attention only to domestic installations where load currents will be relatively light so that I can understand better the consequences of not doing so in that particular environment. I refer to regulation 521.5.1 and item 4.17 on the condition report inspection schedule
There is not a serious outcome unless the steel is fairy thick, certainly much more than the 1.5 to 2mm of domestic CUs. The problem is really overstated with modern enclosures, but comes from long ago when switchgear had thick cast iron casings, often 3/8 to 1/2 inch thick. Significant heating is then possible with high current cables, but the circuit reactance is minimal with thin metal. Thick cast iron has much higher losses than thin steel, but changing this suggestion of a problem has never happened, and may still be seen with some heavy duty switchgear. At 60A or even 100A there is not much problem, and as in all heating this is a long term sustained current, not a short peak. Under fault conditions at several kA there is a significant force on cables which are not closely balanced or are through separate holes, but in a domestic this is unlikely to cause any damage. In a large installation with much higher PSSC the force can be very large, sufficient to cause significant physical damage to casings and cables. It should probably be a C3 for domestics, not ideal but not dangerous.
I forgot to say that single conductors should not travel through steel containment as this acts as a long path through the material and losses can be quite high
There is not a serious outcome unless the steel is fairy thick, certainly much more than the 1.5 to 2mm of domestic CUs. The problem is really overstated with modern enclosures, but comes from long ago when switchgear had thick cast iron casings, often 3/8 to 1/2 inch thick. Significant heating is then possible with high current cables, but the circuit reactance is minimal with thin metal. Thick cast iron has much higher losses than thin steel, but changing this suggestion of a problem has never happened, and may still be seen with some heavy duty switchgear. At 60A or even 100A there is not much problem, and as in all heating this is a long term sustained current, not a short peak. Under fault conditions at several kA there is a significant force on cables which are not closely balanced or are through separate holes, but in a domestic this is unlikely to cause any damage. In a large installation with much higher PSSC the force can be very large, sufficient to cause significant physical damage to casings and cables. It should probably be a C3 for domestics, not ideal but not dangerous.
I forgot to say that single conductors should not travel through steel containment as this acts as a long path through the material and losses can be quite high
