We have some Romex wiring in the unfinished section of our basement which runs at right-angles to the joists above. It is secured with staples on the bottom of the joists, which I understand to be against code for wire sizes less than 6-2 or 8-3. I have a few questions relating to this situation, and would be grateful for some guidance...
1/ I understand that if I install running boards, the Romex can be stapled to those, and everything will be code. Would it be sufficient for this boards to go between the inside faces of the joists, perhaps affixed with pocket hole screws in their ends, or must they actually run below the bottom of the joists? Also, since code only demands stapling to the running boards every 4 feet or so, how does this provide any more support than stapling to each joist, given that the joists are considerably closer than 4 feet?2/ Would it also meet code to cover the wiring, perhaps with some sort of partial plywood ceiling, mounted on but spaced away from the joists? This would ensure that the wiring would be inaccessible, but I'm not sure it would remove the requirement for no stapling.
3/ How long has the no-staples rule been around? All this wiring was done by reputable licensed electricians, as far as I can tell, and so was it installed prior to this rule being established? Or the rule more honored in the breach than the observance?4/ Why exactly is this rule in place? I've read a couple of theories, namely that it is to prevent sagging of the cables, or that it is to prevent people hanging things on them. The first seems strange, as stapling to each and every joist provides more support than would be provided, say, by stapling every 4 ft or so on a running board. And if the second theory is correct, simply blocking off access would avoid this danger.
As I say, any comments would be welcome.