Conduit pricing above 2"

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Gohanto

New User
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United States
Hi, been following the forum for a while, but never posting. I work as a consultant designing audio-video systems and we draw all the associated conduit / box for bid documents (generally new construction, all commercial work for spaces like auditoriums, hotels, broadcast studios, etc.). We'll size all AV conduit directly on our drawings to simplify take-offs for EC's bidding the job. I've run across advice a few times that conduit prices larger than 2" rise quickly, and that I'm generally better off running multiple 2" conduits vs. a single larger conduit like 3" or 4".

From what I've read, this is mostly due to project specs commonly requiring rigid conduit instead of EMT for anything larger than 2", and that those larger conduits require 2 guys to mount each pipe instead of 1. Going from a lot of hear-say though, so was curious to hear from the guys here if that's actually accurate.

In many cases, multiple 2" conduits vs. 1, 4" won't make a difference for AV wiring, but I was curious how it impacts the EC's time and cost.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
In my experience the cost conduit over 2" goes up exponentially. 2" is much faster and easier to work with especially if it is overhead in a ceiling. I am guessing that 2- 2" conduits would be cost effective but I would have to do a cost projection to be sure. Labor, I am betting would not be much different between the two items.

Hopefully someone who has more experience with 4" can chime in.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I don't know why anyone would spec RMC over EMT if the size were above 2". Yes RMC is heavier much more expensive and much more labor intensive to install. EMT larger than 2" will require a large bending machine if bending is required.

If you want to replace a 4" EMT with several 2" EMT's you would need at least 4-2" to get close to the internal cross-sectional area of 1-4" EMT. In many instances running 4 smaller EMT's instead of just 1 large one probably won't save you any money. For riser conduits we almost always run 4", couldn't imagine doing this in 2". :)

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kwired

Electron manager
Location
NE Nebraska
Many people have bending and threading equipment for 2 inch. Not so many have such equipment for over 2 inch.

Pick up a piece of 2 inch RMC - it is a little heavy but manageable in most instances for one person, now pick up a piece or 4 inch RMC, and think about how much work it is to make a run even with no bends or threading compared to maybe making multiple runs of only 2 inch, then look at the actual material cost comparisons.

Bigger raceway will also have more difficulties with pulling conductors/cables if you assume you are using a majority of the volume of the raceway, but if a large conductor/cable is necessary regardless then you don't always have much choice of what it can be pulled through.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Since the op suggested 3 or 4" conduit I was thinking 2- 2" conduits would do the trick. Is that was enough space then imo that would be a cheaper install. If you had to run 4 runs it probably wouldn't be as cheap.

With av wiring , IMO, I would rather have multiple pipes so you are not dealing with tons of wire in one conduit./ I also wonder why rigid instead of emt or even pvc in a slab
 

kwired

Electron manager
Location
NE Nebraska
I have not run 4 inch RMC or 4 inch EMT, but would guess there are similar relationships when comparing to 2 inch of either raceway type.

I have run 3 inch and 4 inch PVC - typically underground which has challenges over 2 inch and smaller but you kind of get away with some things underground that you maybe don't want to have to see if it were above ground even with 2 inch and smaller, plus PVC is just easier in general to handle then RMC or EMT.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
Hi, been following the forum for a while, but never posting. I work as a consultant designing audio-video systems and we draw all the associated conduit / box for bid documents (generally new construction, all commercial work for spaces like auditoriums, hotels, broadcast studios, etc.). We'll size all AV conduit directly on our drawings to simplify take-offs for EC's bidding the job. I've run across advice a few times that conduit prices larger than 2" rise quickly, and that I'm generally better off running multiple 2" conduits vs. a single larger conduit like 3" or 4".

From what I've read, this is mostly due to project specs commonly requiring rigid conduit instead of EMT for anything larger than 2", and that those larger conduits require 2 guys to mount each pipe instead of 1. Going from a lot of hear-say though, so was curious to hear from the guys here if that's actually accurate.

In many cases, multiple 2" conduits vs. 1, 4" won't make a difference for AV wiring, but I was curious how it impacts the EC's time and cost.

i can't imagine why anyone would specify low voltage raceway in GRC,
unless it's sensitive military or government fiber or data lines.

that being said, pvc conduit is often used for data raceways, as it's really
fast and cheap to run, relatively speaking.

4" GRC, last week was about $13.50 a foot. and you've got to cut and thread it.
a decent 4" threader is about $9k. $11k for the bender.

and you've got to spin it up. i had to run 4" & 2" GRC last week, 25' up in the air,
it was an awkward location on the end of a conveyor. guess the amount of time it
took......

 

kwired

Electron manager
Location
NE Nebraska
Is that for a quarry? Are you running 3 struts side by side for strapping? I've never seen that before.

Can't say I've seen it before either, but will say you have to ask if the strut is supporting a 4 inch RMC or if the 4 inch RMC is supporting the strut in most any case that would be similar looking to what was pictured.


Add:
Though I guess in that photo the strut is supporting the conduit - it doesn't end in any thing on either end and would definitely fall down without the strut.
 
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Fulthrotl

~Autocorrect is My Worst Enema.~
Is that for a quarry? Are you running 3 struts side by side for strapping? I've never seen that before.

a gravel pit... yeah, three 1 5/8" side by side at each end.

i've got 4" kellums going on that for support for two cables, the big one
is 500MCM three conductor with grounds, mine rated. feeds a swiveling
stacker that needs 400 amps of 480 three phase, and it has to be up in
the air where equipment can't hurt it. it's gonna be supporting about
90' of the stuff... a fair bit of weight.

three pieces of strap was quicker and less grief than fabricating a 4" square
i beam.
 

cadpoint

Senior Member
Location
Durham, NC
I frankly find it odd that you have to put your work in pipe. Usually it's just free air and hoops.

In the worst conditions the smart wire was in a cable tray!

The only large pipe was where the free hoops had to go through a rated wall into a joint power/tele. room, and we usually throw in a pair of four inches.

Yes it might be expensive to use a fire rated penetration, but it came by the spec's
and again I can't believe it always it had to be in pipe from end to end.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
there is no way in hell that 1,500# of SO cord is going to go 25' up in the air, and back down again...
so, the pipe had to come down, and the cable pulled thru it.


400.8 Uses Not Permitted. Unless specifically permitted in 400.7, flexible cords and cables shall not be used for the following:


(6) Where installed in raceways, except as otherwise permitted in this Code


Sorry ..... :ashamed1:
 
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iwire

Moderator
Staff member
Location
Massachusetts
Fulthrotl,


I owe you an apology, I was trying to quote your post above this one and must have hit the 'Edit' button. They are side by side for us mods.

I did not intend to edit / delete / screw up, your post above. I was just wondering about the code compliance of running the cord in the conduit.

Please feel free to repost your pictures, I cannot restore what I messed up. :ashamed1:
 

Fulthrotl

~Autocorrect is My Worst Enema.~
Fulthrotl,


I owe you an apology, I was trying to quote your post above this one and must have hit the 'Edit' button. They are side by side for us mods.

I did not intend to edit / delete / screw up, your post above. I was just wondering about the code compliance of running the cord in the conduit.

Please feel free to repost your pictures, I cannot restore what I messed up. :ashamed1:

tain't no big deal..... yeah, the cord isn't allowed in a raceway, but there isn't any other way to get it up there.
call it a 10' support sleeve..... doesn't end in a box, doesn't start in a box, just keeps the cable out of the rocks.
the inspector looked at it when i put it up there, and as long as the cable is mine rated, he's good with it.
took the 90 off the end of the conveyor, and just put a strain relief up on the end of the pipe, and the cable swags
out to the end of a triple unistrut arm with a guide on the end of it.

i'll post a thread on the entire thing when it's done... this was a blatant threadjacking....
not that i've ever done that before.... :ashamed1:

got the little cable up there today, and all the brackets, strut and whatnot is welded.
got one feeder from the underground vault pulled up to one control panel, and the
next one is tomorrow..... tuesday, the UL field inspector shows up for his pre certification
walk thru with the certification a week from wed... busy time.

it's 5:30 pm, and i'm gonna eat dinner and go to bed... i'm pooped, and i gotta get up at
3 am tomorrow.... :rant:

 
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