Code of the day NEC 300.4

[Jpflex]

I've wondered about this code before and it may also appear to be a catch 22 because codes may conflict here.

For example conduit is required to run along its supporting surface and be supported and secured within so many feet. However, if you were to use wet listed self tappers (with rubber gasket) and hole straps to the metal roof directly you would violate this code. You would meet the securing and support code while failing the 300.4E

Perhaps placing unistruts between the corrugated roof and conduit may help with this but should holes really be made in corrugated roof?

 

[infinity]

You have three basic choices use RMC or IMC or use something to provide the require 1.5" spacing like strut. The holes in the metal are not an issue. The roofing material is held down with long screws through the decking which is why this entered the code in the first place. The roofing screws can penetrate the deck and then pierce the EMT fastened directly to the metal decking. This code change drastically changed how these conduit and cable runs were installed.

 

[jaggedben]

...

For example conduit is required to run along its supporting surface ...

Where are you getting this from?

 

[Jpflex]

You have three basic choices use RMC or IMC or use something to provide the require 1.5" spacing like strut. The holes in the metal are not an issue. The roofing material is held down with long screws through the decking which is why this entered the code in the first place. The roofing screws can penetrate the deck and then pierce the EMT fastened directly to the metal decking. This code change drastically changed how these conduit and cable runs were installed.

How then would you secure and support conduit ran below corrugated roofing?

 

[infinity]

How then would you secure and support conduit ran below corrugated roofing?

RMC or IMC can be one hole strapped directly to the underside of the metal pan with self drilling screws. If running EMT then you'll need 1 5/8" strut or something else fastened to the metal with self drilling screws.

 

[LarryFine]

Or I'd ask why it can't be attached to the structure supporting the roof, typically bar-joists.

 

[augie47]

Most often here corrugated roofing is supported by metal trusses and there are a number of Caddy hangers that can be used.
(typed at same time as Larry's post)

 

[infinity]

Most often here corrugated roofing is supported by metal trusses and there are a number of Caddy hangers that can be used.
(typed at same time as Larry's post)

Yes Caddy does make some products if you want to not use strut. You could also use a Minerlac strap and short rod if you're running a single conduit. Below are the fasteners that you're trying to avoid.