NM cable on a rooftop

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dana1028

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Location
San Francisco Bay area
See photos - this is NM cable running over a somewhat flat roof [no attic space] - being protected with steel angle and tubing. When finished with the wiring, a new roof [foam? tar & gravel?] will be put over the top.

Is NM cable permitted in this application? I think not, but would like your opinions. ThanxNM - rooftop.jpgNM - rooftop1.jpg
 
I agree with 300.9.

But the angle iron is not a raceway and technically under the roofing material it is a dry location, or else the roofing material is not doing it's job.
 
Are they installing new joists across the blocks shown? Or will composite roofing be applied directly over the angle iron and what looks like a gas line too?
 
dana1028 said:
See photos - this is NM cable running over a somewhat flat roof [no attic space] - being protected with steel angle and tubing. When finished with the wiring, a new roof [foam? tar & gravel?] will be put over the top.

Is NM cable permitted in this application? I think not, but would like your opinions. ThanxView attachment 7985View attachment 7986
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hillbilly1 said:
Are they installing new joists across the blocks shown? Or will composite roofing be applied directly over the angle iron and what looks like a gas line too?
Click to expand...

From what I can tell foam insulation, tar & gravel to be applied directly over the angle iron.
 
What about condensation? I know under the roofing material this certainly should be dry. However, the heated cables [winter time] would be expected to create condensation within the raceway [tube channel]....wouldn't it?

We [forum] constantly speak of condensation being the 'wet' issue of conductors in raceways.
 
dana1028 said:
What about condensation? I know under the roofing material this certainly should be dry. However, the heated cables [winter time] would be expected to create condensation within the raceway [tube channel]....wouldn't it?

We [forum] constantly speak of condensation being the 'wet' issue of conductors in raceways.
Click to expand...

What would the difference be between a exterior wall with NM and this roof?
 
Would derating the cable become an issue based on the ambient temperature applied to the cable under the directly applied roof under a protective plate? Even if NM is used, conductor sizing might have to be considered.
 
102 Inspector said:
Would derating the cable become an issue based on the ambient temperature applied to the cable under the directly applied roof under a protective plate? Even if NM is used, conductor sizing might have to be considered.
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+1. Even without looking at elevated ambient temp between the foam and the current roof surface, you will have effectively embedded the wire into insulation rather than having it in either free air or conduit for heat transfer.
 
Eichlar Homes

Eichlar Homes

Here in the bay area (San Jose CA) all the old Eichlar homes were wired that way because of flat roofs. Angle iron directly on top of tongue and groove. Foam/tar roof right over all of it. Some of that wiring is 50+ years old and still going.
 
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