The vertical posts are usually 6x6 or 4x6 posts. The horizontal boards are 2x4, laid flat against the post. This creates a 1.5" space between the vertical posts and the exterior steel siding. In the past, we've asked inspectors about wiring methods in these buildings, and have been given permission to run our MC cable horizontally, stapling to the top or bottom of these horizontal frames. We are not keeping the 1.25" clearance as required by 300.4(D), but I've always thought they allowed this because it is unlikely that new screws/nails will be installed on this finished building. Alternatives would be to run every wire vertically only, or staple on the interior of the 2x4s and drill through each post, or run emt, or...?
I just failed an inspection on some stapling problems in a pole barn. I have yet to verify the exact problems, as this inspector has previously allowed the horizontal top/bottom method in the past.
Any thoughts on wiring these? Are other inspectors specifically allowing this method or not?