Installing conduit on ceiling

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paulie01

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I am doing a job which involves installing emt conduit on the metal ceiling of a big garage. Can I mount the conduit on the metal ceiling or do I have to allow a space for future roofing screws to be installed.
 
paulie01 said:
I am doing a job which involves installing emt conduit on the metal ceiling of a big garage. Can I mount the conduit on the metal ceiling or do I have to allow a space for future roofing screws to be installed.
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Check this out

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).
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I forgot to mention this is for a fire alarm system, I assum the 1900 boxes for the smoke detectors must also be mounted 1 1/2" below the ceiling not directly on the ceiling.
 
paulie01 said:
I forgot to mention this is for a fire alarm system, I assum the 1900 boxes for the smoke detectors must also be mounted 1 1/2" below the ceiling not directly on the ceiling.
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The rules are for conduit and racways, but it does state a cable or raceway "wiring method"...? The screws the roofers use are very long and could drill thru a box, so I would space boxes as well.
 
If there is a way to attach standard deep strut I would use that as my standoff for both the boxes and the conduit. I space my mounting struts a bit under the required spacing distance for the emt and the whole thing looks like it ought to be there and works quite well.At least to me that the cleanest way .
 
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