Steel Conduit Installation Questions

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Jon456

Jon456

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Colorado
Excuse me if this is the wrong forum for these questions, but there doesn't appear to be another forum to address installation, techniques, and other industry "best practices" that are independent of the NEC requirements. (Perhaps Mr. Holt or one of the moderators will create such a forum.)

My questions have to do with installation of steel conduit, primarily with regard to fittings. I posted a list of questions yesterday in another self-help Web site (because I wasn't sure where to post my questions here), and I did get one well-informed response. But there are still some unanswered questions, and I'm sure the combined experience an wisdom on this site will quickly resolve them for me. :wink:

1. Regarding compression fittings for joining or connecting EMT, I know there are special raintight, liquidtight, and concrete-tight fittings. But the compression fittings I'm looking at have no specific application listings, neither on the package nor on the fitting itself (nor on the manufacturer's Web site). So does that mean these "regular" compression fittings are only for dry environment use? If so, why would you use one of these compression fittings instead of the set-screw type fittings? Obviously cost must be a factor in this decision. And the gentleman who replied on the other forum did mention that the compression fittings form a tighter, more secure joint (which is why I prefer them). But what are the reasons when you would be compelled (either by code or by "best practices") to use "regular" compression fittings instead of set-screw fittings?

2. Threadless, set-screw type conduit fittings are available as either die-cast zinc or formed steel. Are there specific applications where one type is preferred (or required) versus the other type? It seems to me that steel would always be better as I've seen many die-cast fittings in old work that were split from over-torquing. (I have to wonder if some of the fittings might have split some time after the actual installation due to thermal cycling, accumulated stresses, and/or fatigue.) The gentleman on the other forum stated: "die cast fitting tend to fit tighter on the pipe and are generally preferred in my area." But I'd like to get more feedback on this.

3. I can see the physical difference between an LB conduit body and an SLB Service Entrance Elbow. But besides being able to flush-mount an SLB (and the fact that an SLB is smaller than an equivalently-sized LB), are there any other differences in the use of these two fittings? What is it about the SLB that makes it specific to the service entrance? (Is it because the LB is designed to contain splices and the SLB is not?) Given the choice, would you prefer an LB over an SLB to gain the additional volume for bending wires? Or would you prefer the SLB for the convenience of the flush-mounting (and its lower cost)? Note that for the application where I want to use one of these, the conduit body I select (either SLB or LB) will not contain any splices; I just need it to change direction on the conduit run.

4. What size screw is commonly used to secure one-hole mounting straps for 1/2" and 3/4" EMT? I initially selected #10 sheet metal screws (for attaching to metal framing), but the #10 screw was swimming in the large 1/4" x 5/16" elongated hole that is factory-punched in the mounting strap. Would a #12 or #14 screw be a better choice? The gentleman on the other forum replied that he doesn't generally worry about the sloppy hole and "as long as you can use the screw to tighten the clamp, you are fine." This seems like a perfectly reasonable answer. But I thought I'd throw the question out again here for additional opinions.

Thanks in advance for all replies! :smile:
 
4: We typically use the screws that come in the red anchor kits, as a 'universal' screw. We can get the anchor kits with 100 screws and 100 anchors for cheaper than 100 screws by themselves, so we have a lot of leftover anchors (and bits). Maybe if we bought the screws 10,000 at a time it'd be a better price than all those anchor kits, but the leftover masonry bits (one in every kit) come in handy, because you can't typically drill 100 holes into brick with the same bit.

I looked on the box, and the screws are listed as 10 x 1" Hex/Phillips/Slot SMS. (the anchors are #22 8-10-12 Red Collar)

They go great into wood, metal, or into the anchors into concrete, stone, brick.

We also use self-taping screws where required. When the steel studs go up on a job, we just "borrow" metal taping screws (with permission, of course) from the framers to zap boxes and straps to studs, where we aren't using caddy clips. On any given job, we'll use 1 screw to the framers 100, so they never mind us taking a handful here or there.

I agree with you that they don't fit the holes in the straps exactly, but I also agree with your previous respondent who said "as long as you can use the screw to tighten the clamp, you are fine."


Edit:

#2: simple answer- whatever the supplier drops off the truck for us, unless the architect has specifically required one or the other. Our spec books include sheets on both products where the architect doesn't specify, and usually they don't. When they do specify, they often want steel compression fittings everywhere, but that doesn't happen often.

Just my two cents. I'll leave #1 and #3 for others better qualified to answer.
 
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1. Compression fittings used to be called "raintight". That is until a couple years back the someone decided that goofy little O-ring is needed for raintight applications. Other than that, compression is more expensive and takes more labor to install. I've always preferred steel set-screw myself. Some jobs spec certain fittings and that is what you must use, unless you submit and get approved a variance.

2. The zinc die cast fittings were cheaper until the price of zinc went through the roof 3 years ago. Now it doesn't make sense to use them, since they cost more than steel fittings.

3. I generally use LB type condulets. There are times, though, where an SLB is just the right fitting for the job. As far as splicing, if it has the cubic inches listed on the fitting, it's code legal to splice in them if you meet your wire fill.

4. #10 LR screws work fine. Culley makes a screw called a washer-head that is a bit larger.
Culley.jpg
 
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1) The choice is often made by the job specs.
2) Again job specs. Set screw are often cheaper. One issue can be the use of vacuum fish tape sytems. Set screw couplings often leak too much to permit the use of the vacuum on longer runs, unless you tape the joints.
3) For conductors sized #4 and larger, often even a standard LB is not permitted to be used by the code rules because it is too small. See 314.28(A)(2)&(3).
Don
 
For most of these my answers would be the same as Paul's. But as for screws and straps. On exposed masonry or concrete I usually stick to the kits on small jobs - larger jobs with noise not being an issue I shoot them in.

On steel stud work if either using pipe or MC that will be covered by rock I don't use straps at all. I just use tie wire and lash them as a support. Either to the side of the stud by drilling a hole or two if not near a pre-punched one, or do one of two things for multiples in the same stud bay... A hanger bar (Caddy TSGB16), or a piece of scrap EMT through some holes I'll punch in both studs with a stud punch, and just lash with tie wire to that... Why waste straps if it doesn't need to pretty, although beauty is often in the eye of the beholder of the wallet....

As for lifting/stealing/borrowing screws from the framers - why not go on down to their supply house and grab a box - it may take a year to go through a 25# BULK box <$100 - (SEVERAL THOUSAND SCREWS) keep the whole box at your shop or in your truck just don't spill 'em and drive over them.... :grin: But yes those black metal "framers" or "Streakers" do the job faster/better than most electrical suppy house stocked sheet metal screws. And buying in bulk will save money and time if you are never going to run out of screws. Time and hassle is money.... And the Framers won't give ya the dirty eye as they pull off the job and make sure not to leave a single one....

While you're at it load up on a year or so's worth of every other screw you use often too... YOU'LL USE THEM EVENTUALLY....

Personally I like #10 hex head self-tapping as an all-a-round screw - they don't wabble much when starting and don't cam out like phillips head - go ahead and use them on metal - in wood - even in anchors.... And stick to "Streakers" in tin can stud work.

http://www.grabberman.com/
 
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I would always choose a steel set screw fitting if I had a choice. Small die cast fittings cost more than steel and fail more. Steel fittings are a great help if you are installing EMT by yourself.
The only time I like compression fittings is on a demo job. They come apart faster and you dont have to move your ladder as much because you can sometimes unscrew several lengths at a time.

For roughing metal studs, I would use framimg screws (ones I buy) and the pre-cut pieces of gavlanized tie wire. I prefer tapcons for masonary (1/4" x 1-1/4" for block and concrete, 3/16" for precast) and tek screws toggle bolts and zip its for most everything else.
I avoid LBs as much as possible for bigger stuff. I consider SLBs and LBs for small EMT interchangable and cant ever remember having to splice in one.

Thanks for te heads p about the LB size fill restrictions.
 
Jon456 said:
4. What size screw is commonly used to secure one-hole mounting straps for 1/2" and 3/4" EMT? I initially selected #10 sheet metal screws (for attaching to metal framing), but the #10 screw was swimming in the large 1/4" x 5/16" elongated hole that is factory-punched in the mounting strap. Would a #12 or #14 screw be a better choice? The gentleman on the other forum replied that he doesn't generally worry about the sloppy hole and "as long as you can use the screw to tighten the clamp, you are fine." This seems like a perfectly reasonable answer. But I thought I'd throw the question out again here for additional opinions.

Thanks in advance for all replies! :smile:
Click to expand...


We use these self-drilling screws specifically designed for the larger hole in the strap:

1430.jpg


http://www.erico.com/products/CADDYcfcWaferHead.asp
 
paul said:
I generally use LB type condulets. There are times, though, where an SLB is just the right fitting for the job. As far as splicing, if it has the cubic inches listed on the fitting, it's code legal to splice in them if you meet your wire fill.
Click to expand...

I've been reading NEC Article 314 and came across this:

314.5. Short-Radius Conduit Bodies. Conduit bodies such as capped elbows and service entrance elbows that enclose conductors 6 AWG or smaller, and are only intended to enable the installation of the raceway and the contained conductors, shall not contain splices, taps, or devices and shall be of sufficient size to provide free space for all conductors enclosed in the conduit body.

But that leaves me questioning: how do I determine if the conduit body is of sufficient size to provide free space for all conductors enclosed? I know how to calculate conduit wire fill based on cross-sectional area, but I'm not clear how to calculate conduit body fill based on volume. Could someone point me in the right direction on this?

To use a real-world example, I need to run three 6 AWG conductors and one 8 AWG conductor in a raceway. By my calculations, 3/4" EMT will suffice. Before, I assumed that any 3/4" conduit body would be appropriately-sized by the manufacturer to accommodate any code-compliant wire fill in 3/4" conduit. But now I'm not sure. So back to my example... I want to use a 3/4" SLB in my run; this SLB is marked "Vol 3.8 cu in". How do I calculate (or in waht tables do I look up) the fill value based on the sizes and number of my conductors to determine if this SLB will be code-compliant?
 
Jon,
Look at 314.16(C). When you are using conductors #6 and smaller and not splicing in the conduit body a conduit body of the same trade size as the conduit is sufficient.
Don
 
had a problem several years back when using 4in set screw couplings on a 300ft run when we tried to use a vacuum to pull a mouse through we could not get enough suction had to use duct tape to seal the couplings
 
I think at one time or another I've seen just about every kind of these screws (that have been shown on this thread) being improperly used as terminating methods for equipment grounding conductors. :smile:
 
lpelectric said:
I think at one time or another I've seen just about every kind of these screws (that have been shown on this thread) being improperly used as terminating methods for equipment grounding conductors. :smile:
Click to expand...


I would argue that some self drilling screws into the back of a metal box make a tighter connection than the 10-32 green machine screws typically used for grounding.
 
Jon456 said:
I've been reading NEC Article 314 and came across this:

314.5. Short-Radius Conduit Bodies. Conduit bodies such as capped elbows and service entrance elbows that enclose conductors 6 AWG or smaller, and are only intended to enable the installation of the raceway and the contained conductors, shall not contain splices, taps, or devices and shall be of sufficient size to provide free space for all conductors enclosed in the conduit body.

But that leaves me questioning: how do I determine if the conduit body is of sufficient size to provide free space for all conductors enclosed? I know how to calculate conduit wire fill based on cross-sectional area, but I'm not clear how to calculate conduit body fill based on volume. Could someone point me in the right direction on this?

To use a real-world example, I need to run three 6 AWG conductors and one 8 AWG conductor in a raceway. By my calculations, 3/4" EMT will suffice. Before, I assumed that any 3/4" conduit body would be appropriately-sized by the manufacturer to accommodate any code-compliant wire fill in 3/4" conduit. But now I'm not sure. So back to my example... I want to use a 3/4" SLB in my run; this SLB is marked "Vol 3.8 cu in". How do I calculate (or in waht tables do I look up) the fill value based on the sizes and number of my conductors to determine if this SLB will be code-compliant?
Click to expand...

There have been some times when I wish someone made LB extension Rings
 
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