Running conduit on flat roof

M

Mike410is

Member
Location
Florida
Occupation
Residential electrician
Anyone have advice running conduit on a flat roof and how I can mount my disconnect? I have an A/C unit at a residence that needs a new wire ran to it. The current wire is ran through the ceiling cavity and comes out of a 1in rgd conduit with the disconnect sitting on top of the conduit. I was thinking about running it along the roof to avoid cutting a bunch of holes in the living room ceiling below. Thanks
 
I always try to feed a HVAC (Heating Ventilation Air Conditioning) unit from below to keep exposed conduit from the roof. Most AHJ (Authority Having Jurisdiction) don't like exposed conduit on the roof, since it is a hazard for fire personnel.
 
The disconnect can be mounted on the unit, as long as it is accessible and does not block access to the unit for servicing.
 
mtnelect said:
. Most AHJ (Authority Having Jurisdiction) don't like exposed conduit on the roof, since it is a hazard for fire personnel.
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Almost every flat roof I have seen has a maze of conduits and HVAC units on it. Does this AHJ have any local amendments limiting conduit on flat roofs? Or is this just something the inspectors Express their opinion about but can't do anything about?
 
electrofelon said:
Almost every flat roof I have seen has a maze of conduits and HVAC units on it. Does this AHJ have any local amendments limiting conduit on flat roofs? Or is this just something the inspectors Express their opinion about but can't do anything about?
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Its always interesting and creative getting conduit routed on to a flat roof after the fact but then I always cut 4X4 PT blocks and run EMT, make sure you use 'concrete' type compression fittings and not 'rain tight' as a long level run of conduit will tend to hold water and needs to be 'arranged to drain'.
Many people think you'r required to mount to the HVAC unit often I will look for a place to mount a disco not on the hvac unit so a the back of a poney wall etc. I believe you can be 50' away from the unit.
 
I don't trust EMT on a roof, but I guess if IMC isn't mandated good luck winning a bid with it.
Is there an issue drilling the occasional weep hole on the bottom of the pipe? Making sure it's deburred inside the pipe of course (drill it by an end and file inside)...

Locally, every roof is a maze of pipe strapped to strut that's raised off the roof so many inches. Arlington, Eaton, Centaur at least all sell premade support blocks, but I want to say field-fabricated racks with strut footings were more common, not sure, hazy memory.
 
To me, securing a conduit to a 4x4 block or strut support block that's not secured to the roof does nothing other than create a trip hazard on top of an already poor method of running your conduits.

Jap>
 
jap said:
To me, securing a conduit to a 4x4 block or strut support block that's not secured to the roof does nothing other than create a trip hazard on top of an already poor method of running your conduits.

Jap>
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Mounting conduit on support blocks is a great way to avoid penetrations and potential roof leaks on a flat roof. Not a poor method IMO.
 
pipe_bender said:
Its always interesting and creative getting conduit routed on to a flat roof after the fact but then I always cut 4X4 PT blocks and run EMT, make sure you use 'concrete' type compression fittings and not 'rain tight' as a long level run of conduit will tend to hold water and needs to be 'arranged to drain'.
Many people think you'r required to mount to the HVAC unit often I will look for a place to mount a disco not on the hvac unit so a the back of a poney wall etc. I believe you can be 50' away from the unit.
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Support blocks made from 4x4 lumber, even PT, do not last long on a roof, and will dry out and split over time. Premade rubber or plastic blocks are better IMO.
 
solarken said:
Mounting conduit on support blocks is a great way to avoid penetrations and potential roof leaks on a flat roof. Not a poor method IMO.
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Just sayin, if you fasten the conduit to a support block that's not fastened to the roof what have you gained by doing so?
Take the picture in post #10 for instance.
If you took away all the 4x4 blocks, strut and 1 hole straps would you be any worse off?

Jap>
 
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Mike410is said:
Anyone have advice running conduit on a flat roof and how I can mount my disconnect? I have an A/C unit at a residence that needs a new wire ran to it. The current wire is ran through the ceiling cavity and comes out of a 1in rgd conduit with the disconnect sitting on top of the conduit. I was thinking about running it along the roof to avoid cutting a bunch of holes in the living room ceiling below. Thanks
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If you aren't comfortable with running it through the interior of the building and getting a roofer to install a boot then run it on the surface of the roof using treated four by four stand-offs and pull a redundant ground through the pipe. We always use threaded rigid for roof runs.
 
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