conduit on rooftop

[MGE]

Is there a change in the NEC about running EMT conduit on the roof of a residential condo bldg? The loads are for HVAC units and ex-fans. I was told that to re-work the conduit runs it has to be in RIGID conduit. Is this correct?

 

[petersonra]

There seems to be an urban legend going around that EMT cannot be used outdoors. I think it might be because UL chanegd the rules on how they test the raintightness of EMT a while back.

 

[MGE]

Thanks for the reply. A couple of years ago we only had "Raintite" fittings up to 1" approved by the city inspectors here in SD.
The manufacturers have since complied with fittings up to 4" with a UL listing.
It is a non-corrosive area I think the customer just got bad advice.

 

[satcom]

Is there a change in the NEC about running EMT conduit on the roof of a residential condo bldg? The loads are for HVAC units and ex-fans. I was told that to re-work the conduit runs it has to be in RIGID conduit. Is this correct?

Just be carefull to check if your crossing any expansion joints, roofs can generate a good amount of heat, I have seen EMT on roof tops pull apart at the couplings, IMO EMT is not the best choce for roof tops. I see no problem with short runs of EMT properly supported, something I would want an engineer to seal, before installing.

 

[mdshunk]

I see no problem with short runs of EMT properly supported, something I would want an engineer to seal, before installing.

Okay, now you've got me scratching my head. Who the heck engineers conduit runs? Isn't that the electrician's job?

 

[chris kennedy]

The loads are for HVAC units and ex-fans. I was told that to re-work the conduit runs it has to be in RIGID conduit.

Wouldn't you rather use RNC? The R stands for RIGID. As satcom said pay close attention to expansion joints. And add your own as per 352.44

 

[iwire]

You would almost have to put a gun to my head to use EMT on the roof. I think a lot has to do with the climate but in my area EMT outside will rot out.

Most of our job specs require RMC on roofs.

 

[satcom]

Okay, now you've got me scratching my head. Who the heck engineers conduit runs? Isn't that the electrician's job?

Worked many years of commercial, and heavy industrial construction, and can recall only a few jobs that did not have a plan set for conduit layouts, today many EC's think they can do a design build, without the benifit of a professional design engineer, and of course the expense of plans. Is it done, you bet it is.

We had a strip mall a few years back, where they did a design build, floor plans, and some sectional details, somehow it slipped by the review, winter snow load brought the roof down, did misplaced conduit runs, and mechinical equipment add to the failure?

 

[mdshunk]

....did misplaced conduit runs, and mechinical equipment add to the failure?

I don't know. I give up. Did they?

Did the engineer who sealed the truss plan contribute the failure, by not accounting for equipment that exists on every modern commercial rooftop?

 

[satcom]

I don't know. I give up. Did they?

Did the engineer who sealed the truss plan contribute the failure, by not accounting for equipment that exists on every modern commercial rooftop?

The township cleaned out the entire construction department, after the hearing, my point is conduit runs are not something the electrician lays out on a project, he is not a structural engineer.

 

[iwire]

my point is conduit runs are not something the electrician lays out on a project, he is not a structural engineer.

You must live in another country.:wink:

I also work large commercial and we certainly do lay out our own conduit runs.

Sure occasionally we will have a more industrial job where their is so much pipe work that it is in the design but that is the rarity.

 

[satcom]

You must live in another country.:wink:

I also work large commercial and we certainly do lay out our own conduit runs.

Sure occasionally we will have a more industrial job where their is so much pipe work that it is in the design but that is the rarity.

Yes, I agree it is rare today, there are more jobs being done without design details, it was not always that way, for example, high rise buildings are built today, where the live load is designed so close that even running a exercise class, puts some buildings on the edge, these same buildings need a designers approval to add any structual equipment or conduit.

 

[mdshunk]

... these same buildings need a designers approval to add any structual equipment or conduit.

Must be a NJ thing. I was going to say union thing, but that would have probably been censored, so I said New Jersey instead.

 

[VernB]

I'm aware of several places on the old mill I inhabit with EMT run outside. It's been out there a long time, lots of surface rust but still tight and functional. Personally, I'll take Sch40 PVC for weather exposure if given the choice.

Vern

 

[don_resqcapt19]

Vern,

I'll take Sch40 PVC for weather exposure if given the choice.

If exposed to the sun it won't last as long as EMT under the same conditions. I know that it is sunlight resistant, but the sun makes it very brittle after a few years and then it breaks.
Don

 

[Pierre C Belarge]

Vern,

If exposed to the sun it won't last as long as EMT under the same conditions. I know that it is sunlight resistant, but the sun makes it very brittle after a few years and then it breaks.
Don

Not only does it break, but it discolors and sometimes becomes disfigured, looking like a snake (s-curves).

Roof tops are very harsh environments. In the northeast we have such a diversity of weather conditions, that the electrical work on a roof takes some beating over the years. (sometimes not even years)

 

[dnem]

An Engineer providing conduit sizes for service and feeder runs is expected. . But providing conduit sizes for branch circuits or layout location for any run is micromanagement by the Engineer. . He can spec all branch circuits in conduits ? or lager but beyond that it isn?t practical for him to get more specific.

post #11

post #10
my point is conduit runs are not something the electrician lays out on a project, he is not a structural engineer.

You must live in another country.:wink:

I also work large commercial and we certainly do lay out our own conduit runs.

Sure occasionally we will have a more industrial job where their is so much pipe work that it is in the design but that is the rarity.

Why would you need to be a structural Engineer to lay out conduit runs ?

I?ll say one thing. . As an inspector, I?m not going to be scaling off conduit run specs off of the prints if an Engineer does ?design? the run.

There is alot of information on prints that inspectors should check but scaling plug locations and branch circuit conduit layout design are 2 things that don?t make it onto my list. . If the electrician can?t layout his own conduit runs according to what pipe + wire he needs to arrive at each location in the building and according to what conditions and systems of other trades he actually sees on site, then he should hang his head and walk off the job. . We don?t need an Engineer to ?design? the route and layout of a conduit run. . We need electricians that are able to communicate with the other trades and competent enough to adjust to what is being built.

David

 

[Pierre C Belarge]

David
In "our neck of the woods", we rarely get to see the prints. Even though the state requires prints for jobs, it has never been the practice to let electrical inspectors see the prints.

How do you find the time to look and dissect the prints and then do the actual inspection? It would seem there is not enough time to do both and do both well.

In NJ (I am sure someone will correct me if I am wrong), they have a division that does the plan review and the inspector goes to inspect the work.

In my estimation, to do a really thorough job as an inspector could take the whole day for a commercial project of any size...think about it. The contractor and his men could be on the job for weeks, maybe 1000s of hours of work, plus all of the time spent mulling over prints. The electrical inspector may spend about an hour or so on a job such as this for a rough inspection (possibly without ever seeing a set of prints, and if looking at prints, a fairly brief time at that).

I am not saying the process is a good one, it could use some massaging, but to improve the process would take training and a culture change...all of which costs money.

Just something to think about.

 

[electricguy61]

Around here (N California), EMT is legal, but I run rigid.

1) As mentioned, EMT deteriorates rather quickly.
2) EMT fittings readily pull apart
3) Roofers and other mantenance workers beat the stuffing out of conduits on the roof.

Rigid helps aleviate those problems.

That stated, you have to be able to justify the extra expense. If you couldn't work the added costs into the price, EMT is legal.

 

[satcom]

I don't know how we got off the roof, but I was discussing the conduit, being added to the roof load, and now were discussing conduit in general. And yes we have plan reviews in New Jersey.

"An Engineer providing conduit sizes for service and feeder runs is expected. . But providing conduit sizes for branch circuits or layout location for any run is micromanagement by the Engineer. . He can spec all branch circuits in conduits ? or lager but beyond that it isn’t practical for him to get more specific."

Exactly!