NEC 300.4(E) Exception & NEC 358.12(1)

[erickench]

NEC 300.4(E) states that where RMC and IMC are installed under metal corrugated sheet roof decking, the 1-1/2 inch clearance is not required. I was wondering why EMT or any other metal raceway is not included in this exception. NEC 358.12(1) states that EMT is not permitted to be installed where subject to physical damage. My question is this. Would there be a real problem if EMT were installed under a metal corrugated roof without a clearance? Is EMT more susceptible to damage than RMC and IMC?

 

[RICK NAPIER]

Yes and yes.

 

[Dennis Alwon]

Those roofing screws will go right thru emt and you wouldn't even feel it.

 

[infinity]

NEC 300.4(E) states that where RMC and IMC are installed under metal corrugated sheet roof decking, the 1-1/2 inch clearance is not required. I was wondering why EMT or any other metal raceway is not included in this exception. NEC 358.12(1) states that EMT is not permitted to be installed where subject to physical damage. My question is this. Would there be a real problem if EMT were installed under a metal corrugated roof without a clearance? Is EMT more susceptible to damage than RMC and IMC?

It's been done that way for decades without much of a problem. Is it possible for a screw to penetrate it, yes, but IMO it's not very likely.