Just curious, looking at a recent new build electric install (lots of bunches of wires) - what sort of distance / percentage of circuit length do wires have to be installed in a bunch before grouping factors are applied? I presumed it was like cables passing through insulation - if they pass through a wall or joist for a short distance and are bunched then heat can dissipate without needing to derate - but if more than a certain length of bunching occurs then derating is necessary?