EMT and purlins

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binney

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I am told by what is usually one of my creditable sources that there is a change in the 2008 code that prohibits running conduit above or on metal joists. The reason being that the roofers are running long screws through the roofing material and penetrating the conduits. According to him the conduit must be run below the joist. I can see this being a problem for contractors who run conduit on top of joists perpendicularly.

The example I had, was running a conduit parallel with a Z-purling and laying it in the tray or on the side of a purling. How would this be a hazard and where in the 2008 would any of this be a violation.
 
Look here:

300.4(E) Cables and Raceways Installed Under Roof Decking. A cable- or raceway-type wiring method, installed in exposed or concealed locations under metal-corrugated sheet roof decking, shall be installed and supported so the nearest outside surface of the cable or raceway is not less than 38 mm (1? in.) from the nearest surface of the roof decking.
FPN: Roof decking material is often repaired or replaced after the initial raceway or cabling and roofing installation and may be penetrated by the screws or other mechanical devices designed to provide ?hold down? strength of the waterproof membrane or roof insulating material.

Exception: Rigid metal conduit and intermediate metal conduit shall not be required to comply with 300.4(E).
Click to expand...
 
Here is the new section that was added to 300.4:

"(E) Cables and Raceways Installed Under Roof Decking. A cable- or raceway-type wiring method, installed in exposed or concealed locations under metal-corrugated sheet roof decking, shall be installed and supported so the nearest outside surface of the cable or raceway is not less than 38 mm (1? in.) from the nearest surface of the roof decking.
FPN: Roof decking material is often repaired or replaced after the initial raceway or cabling and roofing installation and may be penetrated by the screws or other mechanical devices designed to provide ?hold down? strength of the waterproof membrane or roof insulating material.
Exception: Rigid metal conduit and intermediate metal conduit shall not be required to comply with 300.4(E)."

As long as you are at least 1 1/2" below the roof decking you would be OK.

Chris
 
300.4 E How come I just finished my code update course and that never came up?

This does make sense, but the runs I had were anywhere from 6-9" below the roofing deck, which should be fine.
 
If you install the conduits 6-9" below the deck you should be fine.

This is the type of installation that section 300.4(E) is trying to avoid.
conduitie7.jpg


Chris
 
binney said:
I am told by what is usually one of my creditable sources that there is a change in the 2008 code that prohibits running conduit above or on metal joists. The reason being that the roofers are running long screws through the roofing material and penetrating the conduits. According to him the conduit must be run below the joist. I can see this being a problem for contractors who run conduit on top of joists perpendicularly.

The example I had, was running a conduit parallel with a Z-purling and laying it in the tray or on the side of a purling. How would this be a hazard and where in the 2008 would any of this be a violation.
Click to expand...

If your referencing the cross brace of the steel truss, I beleive you'll be fine, frankly the word purlin stuck in my mind and frankly took me back after a few minutes of searching.

purlin

I'd run it on top of or under the lower support angles of the truss in a feeder situation, but with just a conduit, > Z-purling, : )

COOL:
I just found a neat trick here, I dropped the full link of the defination in.
I then highlighted and just started re-typing and rewrote the subject item.

purlin
making the internet link via this software not required
 
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