Metal Conduit 101: Fittings and their Uses

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Old 12-08-07, 09:01 PM
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Metal Conduit 101: Fittings and their Uses

Well, if you came looking here to get educated it won't be from me... I have nothing but questions and cannot find answers anywhere so far.

I want to run 1.25" IMC but I have no idea how to assemble the pieces! What couplings does one use, in what order, and how are they attached. The guy at Home Depot was less than useless, none of the seven or eight books I've looked in has these details nor did a Google search turn up much.

Hmmmm... is this a trade secret!? Seriously, if someone can take me thru this with baby steps I'd be very greatful.

The pieces I bought, to help start it off, are (if it matters, all are RMC except 10' section):
2 x 1.25" 10' IMC straight pipe (one end female threaded w/ flare, the other male threaded)
4 x 1.25" 90-degree sweeps (both ends male threaded)
1.25" LB connector
1.25" lock nuts
1.25" watertight connector hubs
1.25" plastic bushings
1.25" coupling connectors (3" short straight pipe w/ female threading on both ends)

I might not be using the right terminology, sorry!

They didn't have any compression couplers in 1.25" or I would have got them too.

So what screws into what? I'm particularly unclear on using the watertight connector hubs, the compression couplers which I don't have!, and the threaded connectors.

I will have to cut the 10' pipe and if I do, how do I deal with the loss of the threading?

Oh, and I must use steel pipe as I will be only going 6" down under 2" of concrete... residential walkways only.

Thanks in advance!!
 

Last edited by DavidT; 12-08-07 at 09:28 PM.
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Old 12-09-07, 07:41 AM
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Give us a description of the work you are doing.
This will help when describing the installation procedure.
Are you coming from a panel, where are you going, etc.
Why are you using IMC/RMC? You couldn't have asked for a harder installation for a DIY.
 
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Old 12-09-07, 08:19 AM
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I'll bet you don't do well with puzzles.

Really, it is not all that difficult other than bending the conduit (if needed) and ending up with the threads (or lack of them) in the right places or the ability to thread the pipe .

So what screws into what?
very simply put: whatever you need to go next.

I'm particularly unclear on using the watertight connector hubs,
you may not even need these. If you are entering on the bottom or side of a 3R rated box, you will not need them. If entering the top, they are used to prevent water from entering the box from above.

compression couplers which I don't have!,
generally used to replace the threaded couplings when you cannot thread the pipe where you have a coupled joint.

and the threaded connectors.
entering a j-box when you have a threaded end of pipe. A compression connector can be used in place of this if you end up with non-threaded end at the j-box.

I will have to cut the 10' pipe and if I do, how do I deal with the loss of the threading?
that is where the compression coupling comes in. As long as the fitting is "listed" for use in a wet location.

Oh, and I must use steel pipe as I will be only going 6" down under 2" of concrete... residential walkways only.
I'll let you make that call

layout is the most important part of a job when working it in the fashion you are. when looking to install, you should know where everything is going so the parts you want to use end up in the correct place.

also, the big box stores maybe able to thread for you. The taper is 3/4 in/foot (which is a standard N(ational) P(ipe) T(hread) Electrical conduit is not intended to seal like a plumbing pipe but needs to be wrench tight to cause an electrical connection. 2 pipes in a coupling will actually run into each other because the coupling is not a tapered thread. The fittings will jam on the pipe but they do not necessarily seal. Because of that, when rotating a pipe. the fittings do not have to be so tight as to effect a watertight seal.

also, be sure to ream the ends of any pipe you cut. Use plastic bushings on all exposed ends (like in a j-box) including on fittings. (there are rules for when and when not but simpler just to put them on for this install)
 
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Old 12-09-07, 10:17 AM
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Originally Posted by dezwit View Post
Give us a description of the work you are doing.
This will help when describing the installation procedure.
Are you coming from a panel, where are you going, etc.
Why are you using IMC/RMC? You couldn't have asked for a harder installation for a DIY.
The "why" of IMC/RMC is simply that I am replacing an old conduit so the foundation thru holes are already there. One end is under concrete so it is very hard to access. Using IMC/RMC allows the bury to be only 6" under the concrete, which is about where the old one enters the garage.

OK, I will try to describe the exact setup.

Starting from the garage, there is 3'3" of concrete walkway and then 4'9" of soil to the house. The foundation thru-hole in the garage is 6" below the top of the foundation wall. I will need to widen it slightly for the new conduit. The concrete is over 2" thick. Once the install is done, we plan to pour concrete over the soil section above the conduit.

Since the garage run starts 6" below concrete we plan to drive a new conduit pipe from the garage towards the house. Without breaking up the concrete or driving new holes don't see how else to do it than to run steel 6" down.

On the house side, the old conduit starts with a 90-degree sweep at the bottom of the overhead joists and runs down to the foundation thru-hole which is about 1' below. The hole emerges right at grade level, so it will need to drop 8" more (at least) 2" for new concrete, and 6" below that.

If you can advise what components to install and how to fit together it would be of enormous value.

I realize that to anyone who has done this work already, it might seem like it is completely obvious how to assemble the parts, but no where do I find a list of rules/principles for a good conduit install. It was unclear how to make things water tight (apparently, you really don't?)... it was unclear whether you need to have connectors between components or can they just screw together... it was unclear when to use the weather tight connector... it was unclear why compression couplers existed since the pipe is threaded (I get it now)... it was unclear when to use threaded couplers... and so on.

Anyway, I didn't want to guess at how to solve the puzzle, these things are never just intuitive, there are always trade secrets that can't be guessed... and ultimately we just want to do it right.

Thanks so much for your help!
 
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Old 12-09-07, 10:33 AM
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Since you have four feet of dirt I'd just abandon the existing run and do a new one using schedule 40. The experts can tell you just how deep. If your house and garage is wood new holes are easy. If brick and not the newer cheap soft stuff you might have to rent a core drill. I have drilled brick using a masonry hole saw. Drilled pilot hole all the way through with a concrete bit in a half inch drill to use as a guide then drilled as deep as I could from both sides. Any remaining brick I just chiseled out.
 
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Old 12-09-07, 12:14 PM
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Originally Posted by ray2047 View Post
Since you have four feet of dirt I'd just abandon the existing run and do a new one using schedule 40.
I'm open to that but...

How do I deal with area under the concrete walkway? Wouldn't I have to dig it all out under there? I assumed this would be very difficult.

Are you suggesting for the new holes to go thru the wood siding rather than the foundations? I don't want to break the walkway and the garage foundation is level with the walkway and butts up against it so I'd have to drill new hole in garage foundation at least. I could go out house siding though. The foundations of each is laid concrete walls, not cinder block--probably 4-5" thick. House was built in 1906. What would I need to go through the foundation(s)?

Thanks.
 
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Old 12-09-07, 12:25 PM
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depending on the weather, there is a neat little trick using the conduit and a water hose.

water drilling. I have seen it done for 30 or 40 feet. it's messy as all get out but it works.

attach a garden hose to the end of a pipe and allow the water at the other end to wash out the dirt as you progress forward. If there are large rocks, it makes it harder and you may need to restart at a slightly different location but you generally find a way through.

drilling through foundations? you can but you need to be sure it is very well sealed. You do not want the hole to allow water to leak around the pipe.

That is why I often enter above grade.

Anyway, to drill through the concrete. A dry core hole saw is the easiest and cleanest, a wet core saw works as well but is messy.

A masonary drill and lots of patience gets the job done eventually. Lots of holes areound the perimeter of the intended hole and then a hammer and chisel to connect the dots.
 
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Old 12-09-07, 11:16 PM
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Just to clarify I mentioned brick or wood wall because I would definitely exit above grade then go underground. Masonry hole saw wouldn't work on concrete. For that you need a core drill as stated.
 
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Old 12-09-07, 11:37 PM
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I'd never heard of a core drill before but when I did a search the products I found said they were not for concrete, but for block and brick. Am I looking in the wrong place?

What about a hammer drill and SDS bits?
 
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Old 12-10-07, 12:59 AM
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Originally Posted by DavidT View Post
I'd never heard of a core drill before but when I did a search the products I found said they were not for concrete, but for block and brick. Am I looking in the wrong place?

What about a hammer drill and SDS bits?
i been useing the core drill in concrete you have to just ask the rental centre for one they will have one on hand you can use to drill thru the concrete

[ the core bit for drilling thru the concrete will have diffrent type of cutting edge than other verison useally have diamond grits on it and it will cut thru the concrete and genrally with this type you will need water to keep the tip cool and remove the grits from cutting it ]

the hammer drill with the SDS bit will work but if not carefull it can make it worst than it will need to be but with very good bit it should do pretty good job.

Merci, Marc
 
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Old 12-10-07, 10:00 AM
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Back to Basics...

So just to get back to the original purpose of this thread... to understand how to assemble IMC/RMC conduit. Let me see if I understand it now:

The various pieces may be just screwed together using factory threading, without fittings or couplings. ( Are these just hand tightened or is there a special tool as the pipe is just round, no "nuts" built in?)

There is no need for using couplings if two pieces mate with each other directly (e.g. a straight pipe and an elbow can screw directly into each other).

There is no need for any waterproofing other than the tightness of the seal. ( Is hand-tight good enough when mating w/o fittings?) In fact, one should specifically avoid any teflon strip or other threading compound as it can reduce the conductivity of the ground for the conduit. (Here I refer to grounding the conduit, not using it as the ECG.)

Provided it is an all-metal run, the grounded j-boxes on either end combined with locknuts on both sides of the box holding the conduit in place will suffice to ground the conduit. No need for grounding bushing.

When two threaded male sections (for example) meet a female/female coupler can be used to make the connection. These are just round short pipe so I assume the answer for "how to tighten" pipe-pipe connections w/o fittings applies here as well.

Since I will have no outdoor j-box connections, I have no need to use the waterproof hub connectors/couplers. These are only used to enter a box from an exposed knockout (i.e. one not at bottom of box).

Any time there is a non-threaded end of conduit that must be joined with either a threaded or non-threaded mate the compression coupling is used. ( Not sure of case w/ two non-threaded pieces... how do I combine the compression couplings to make a piece w/ two compression ends... or is this a special type of two ended compression coupling? I see a lot of drawings of something that looks like a compression coupling on both ends with a nut in the middle on a threaded portion... what is this? Didn't see in the store. Or are those just for thin-walled EMT not IMC/RMC... in which case do I make the connection as pipe->compression coupling->female/female connector-coupling->compression coupling->pipe?)

( Although I can work around the case, not sure what to do when I have a female-female meeting between components.

Using RMC elbows and other fittings w/ IMC straight pipe is perfectly acceptable.

Plastic bushings must be applied at either end of run where wire enters the conduit.

Warning: I went a little crazy here creating a text syntax for connecting conduit... hope you find it as fun as I did!

[////[ = screwed directly to each other (female->male)
]////] = screwed directly to each other (male->female)
()//= compression coupling
x = locknut
...|*Structure*|... = structure passed through

A run such as this would be acceptable--it starts in house at bottom of overhead joists, runs thru house foundation wall and below grade starting with bottom of LB-connector. First 4' is soil, next 3' is 2"-thick cement walkway adjacent to garage wall. Straight pipe runs thru garage foundation wall below grade (and cement) and makes hard-turn upward via capped elbow up to Panel box. Entire run is 6" below grade... my reading of NEC allows IMC/RMC to run 6" below soil or 2" of concrete. Correct?

===[Bushing[////[90-degree...|*Wall*|...sweep]////]LB Connector[////[90-degree sweep]////]T-connector[////[8-foot Straight...|*Wall*|... pipe()//x]Capped elbow[x//()Straight pipe()//x|*SubPanel*|x//]Bushing]===

Hope that makes sense!
 
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