Steel Conduit Installation Questions

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Old 12-30-07, 05:57 AM
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Steel Conduit Installation Questions

Several questions regarding the "best practices" for installing steel conduit:

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. So does that mean they are only for dry environment use? If so, why would you use one of these compression fittings instead of the set-screw type fittings? (I imagine they'd be better for applications where there's a lot of vibration. Is that correct? Any other applications where one type would be preferred over the other?)

2. Threadless, set-screw type conduit fittings are available in either zinc or 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 zinc fittings that have been split from over-torquing.

3. All the conduit bodies I've seen are threaded. So for use with EMT, does one thread a set-screw connector or compression connector into the conduit body? If so, then I assume the locknut that comes on the EMT connector is removed and not used in this situation. Is that correct? (I guess I should also ask: are there threadless conduit bodies made specifically for EMT?)

4. 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, 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?

5. I have to pass a conduit through an exterior wall and then have it run along the interior wall. I'll be using IMC for the exterior conduit and EMT in the interior. Is it acceptable to Screw an LB (or SLB) conduit body onto the end of the IMC where it penetrates the interior wall, and then attach the EMT to the conduit body (using a compression or set-screw EMT connector) for the interior run? Or do I need to bring the conduit into a wall-mounted junction box? (Note: I will not be making any splices at this point in the run. I simply need to transition from the IMC to the EMT, and make a hard 90 deg turn from perpendicular to parallel to the wall.)

6. 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?
 
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Old 12-30-07, 10:58 AM
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. So does that mean they are only for dry environment use?
possibly. sometime the rated use must be sought out seperate from the container or the actual fitting

If so, why would you use one of these compression fittings instead of the set-screw type fittings?
some engineers like them. They do tend to keep the pipe to act more as a single piece rather thatn multiple disjointed pieces. (tighter fit)

(I imagine they'd be better for applications where there's a lot of vibration. Is that correct?
not really sure. haven't had problems wither way because you should install flex to isolate conduit that is attached to an appliance that vibrates too much.



2. Threadless, set-screw type conduit fittings are available in either zinc or steel. Are there specific applications where one type is preferred (or required) versus the other type?
Money money money. I have had bad die-cast and I have had bad steel fittings. When both are good, it tends to become personal preference

It seems to me that steel would always be better as I've seen many zinc fittings that have been split from over-torquing.
most of the die cast fitting tend to fit tighter on the pipe and are generally preferred in my area.

3. All the conduit bodies I've seen are threaded. So for use with EMT, does one thread a set-screw connector or compression connector into the conduit body?
there are threaded and non-threaded. There are some that will accept a connector or just a piece of pipe.

If so, then I assume the locknut that comes on the EMT connector is removed and not used in this situation.
generaly, yes but I have left the locknut if I had to have the screw pointed in a particular direction.

are there threadless conduit bodies made specifically for EMT?)
yes

What is it about the SLB that makes it specific to the service entrance?
luckily, I have never had to deal with service entrance LB's cuz I do commercial/industrial and a standard LB works fine for everything I have ever done

Is it acceptable to Screw an LB (or SLB) conduit body onto the end of the IMC where it penetrates the interior wall, and then attach the EMT to the conduit body (using a compression or set-screw EMT connector) for the interior run?
yes.


6. What size screw is commonly used to secure one-hole mounting straps for 1/2" and 3/4" EMT?
generally, I do not worry too much about the sloppy hole. When attaching to wood, I often end up with sheetrock type screws which are a lot smaller. As long as you can use the screwq to tighten the clamp, you are fine.
 
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Old 12-30-07, 09:09 PM
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Thanks for your response.

Originally Posted by nap View Post
possibly. sometime the rated use must be sought out seperate from the container or the actual fitting
Hmmm... according to "Guidelines for Installing Steel Conduit/Tubing" published by the Steel Tube Institute of North America:

======
"Threadless fittings intended for use in wet locations are marked “Raintight” or “Wet locations” on the fitting or its smallest unit shipping container."

and...

"RMC and IMC fittings for use in industrial applications involving sprayed mineral oils and coolants are marked “Liquidtight” on the fitting or its smallest unit shipping container."

and...

Threadless fittings intended for embedment in poured concrete are marked “Concrete-tight” or “Concrete-tight when taped,” or “Raintight” on the fitting’s smallest unit shipping container.
======

So if this is an industry standard, it would seem to me that I should find one of the above listed markings on the compression fittings I have, if indeed they are rated for one of these special applications. In the absence of such markings, I must assume that they are not rated for the above listed special applications.

Specifically, the 3/4" compression coupling I have is a Halex #26242. On Halex's Web site, they have a page listing their compression couplings. Note that the model 26242is simply listed as a "Compression Coupling". But two lines below, is a listing for a 3/4" sized "Raintight Connector", model # 26262 (this item appears to be mislabeled on their Web site as the picture clearly shows a coupling, not a connector). If you zoom the picture of the model 26262 coupling, you can see that the metal fitting is stamped "Wet Loc" (which is not stamped on the model 26242 coupling).
 
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Old 12-31-07, 07:44 AM
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well, there are guidelines and there are mandatory rules.

There are also real world situations.

All I can say is what should be isn;t always what is. They should be listed as you say but I have had fittings that were listed per the manufacturers spec's but were not indicated as such.

Did I take a chance by installing these without being able to prove to the inspector Sure. Have I ever had a problem with an inspector tagging me for improper fittings, yes, one time but it had nothing to do with this type of situation.

It was when multiple fittings were utilized to convert from one type of pipe to another and he had a problem with it. I have done this numerous times and he is the only one that had a problem with it. Some inspectors get a burr up their rear about certain things and tag improperly, or they have a unique interpretation of the rules involved but it is generally easier and cheaper to simply fix it rather than contest it to the state level.

btw: the "steel Tube Institute" is not my bible, the NEC is. If the NEC requires it, then it needs to happen. If the NEC does not require it, either through their own publications or by referring to the publications of others, then it is not required in my world, merely suggestested.

NEC requires materials to be "listed". This is generally accepted to refer to a UL, or other accepting listing body's listing. If the manufacturer can support such listing regardless of it being indicated as suggested, it is still listed as required per NEC.

One thing comes to mind. PLastic boxes. I never realized the fire rating applied to these things. There is nothing on the box, container, or even available at any supplier I have asked but a typical plastic box manufactured by Carlon carries a 2 hour fire rating (there are specific info available on their website). That is amazing. I would never have thought that without their info, but it is what it is.

btw, I ran off to OZ/gedney/ egs electrical/neer site. Their raintight fittings are indicated by a ridge on thier fittings, so, yes, ther are different fittings and it is a requirement they be UL (or other accepted body) that they be listed as raintight but I find no requirement per NEC to mark the fitting or the container as to the raintight listing.

what you have found through your investigation that the fitting you have are NOT listed for raintight use as evidenced by the info on their website so get the correct fittings.
 
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