Using Rigid Metal Conduit & PVC

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Old 06-19-07, 11:16 AM
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Using Rigid Metal Conduit & PVC

I want to add a weatherproof receptical in my garden area to supply current to a waterfall pump. I will be getting power from gfci thats installed on the brickface of my home.
To accomplish this, I need to dig a trench in my garden area towards a concrete patio, that is 7-1/2 feet wide, then knock out a 12 inch hole in the concrete at the base of my front wall and dig out to a depth of 12 inches.

Here's the part I have not figured out yet:
I need to drive 1/2 inch rigid metal pipe (for 14-2 conductor) 7-1/2 feet under this concrete. Now My question is; once I am through to the other hole and if I do not mess up the threads on the pipe, is there a transition fitting to go from rigid metal pipe to Pvc? If so, what is it really called?
I would prefer to use pvc on the rest of the circuit and leave the pipe in the ground. I also will use uf cable. Is 1/2 inch pipe ok for fishing and pulling 14/2 romex uf cable?
Your replies with any tips, greatly appreciated.
 
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Old 06-19-07, 04:59 PM
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a female adapter on the PVc would allow the rigid to screw into it.

can't figure out why you want to use UF inside of conduit but I would go 3/4 if you are going to.

be sure the steel rigid conduit is bonded to the EGC (equipment grounding conductor)

either leave a rigid coupling on the pipe or actually use a cut off piect of rigid coupled with the good stuff via a rigid coupling. The problem you are going to have is dirt in the pipe.

an easier way to do this is hook up the steel rigid to the garden hose and allow the water to "drill" the hole for you.
 
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Old 06-19-07, 05:50 PM
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Nap,
I need the conduit to drive through the soil and under the concrete; so I figure it would be ok to leave it as it is and not try to pull it out. The soil may be disturbed if I try to remove it. That's why I ask about the adapter for metal conduit to pvc.

I know of the water to do the drilling but some of the neighbors (we all have row homes) are getting water in their basements from excessive rain and I am reluctant to use this method.

Have you had difficulty or know of others who have use 1/2 inch pipe for fishing and pulling 14-2 conductor romex? I feel comfortable using uf cable even though it will be protected.

Does the NEC allow either the choice of pvc or rigid metal conduit to come up through concrete?
 
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Old 06-19-07, 06:38 PM
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you can not use NM (Romex). I would use thwn (single conductors).



I understand what you are doing with the conduit and yes, I would leave it in and use it as well. I hate to go to that much work for naught.

either conduit would be acceptable to pass through the concrete but steel offers much better protection above the ground. A stone thrown by the lawn mower can break PVC.

what I would do.

break your hole in the concrete and dig down. Dig down outside of the pad. Attach the conduit (actually you may be able to use PVC if water drilling) and drill it until you get to your dug hole. There I would have a pre-assembled unit with a steel riser connected to either a steel or PVC 90 and connect the underground pipe to that using, if steel 90, a female adapter on the straight pvc pipe or if a pvc 90, a simple coupling glued onto it and onto the straight pipe.

to attach threaded steel pipe to pvc, you use a "female adapter". it glues onto the pvc and has internal threads the steel screws in to.
 
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Old 06-19-07, 06:54 PM
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I would use rigid through the concrete, since it's less likely to break as the ground settles. Since you are in Philly, you are subject to freezing, which can also break PVC. If you're using rigid underground, you might want to run rigid up above the surface and transition to PVC at that point. You transition with a coupling and a male PVC threaded to slip adapter. Or, you may be able to use an expansion coupling, which is expensive, but will protect your plastic section from breakage. A female threaded adapter screwed onto a rigid pipe is more subject to breakage if overtightened, subjected to stress, cold, heat, blah, blah, blah.

If you use rigid all the way, you will have to screw the rigid into the box extender before you attach it to the wall. I don't think you can use a union coupling on electrical.

I wouldn't use 14-2 UF in a 1/2" pipe. You can probably do it but you'll need some lube to get around the corner and a bushing at the insertion point so it doesn't get abraded by the rigid.

I would just pull 12 AWG THWN, in which case you can easily upgrade to 20A when you decide you need a bigger pump, UV filter, spitter, O2 pump, lighting, and so on. Better yet pull in two hots so you can put your timer by the house.

Also consider upgrading to 3/4" pipe.

If you're going to drive it in, use couplings to thread nipples on either end. Cut the lead nipple at an angle so it has a point. To avoid the threading issue, if you have relatively consistent soil, maybe you can try 3/4" Sch 80 PVC.

To avoid water buildup while "drilling" keep a shopvac handy so when water collects in your "sump" you can suck it out. If you're getting water in the basement when it rains, something is wrong with the grading, foundation drains or gutter conductors. Ok, I'm done now.
 

Last edited by ArgMeMatey; 06-19-07 at 06:58 PM. Reason: Editing errors
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Old 06-19-07, 07:44 PM
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Thanks Both,
I will use 3/4 pipe on your recommendations and also will use rigid metal conduit up from the hole in the concrete and then switch over to pvc about 2 to 3 feet above the concrete back towards the GFCI for power. But on the new receptical side which will be in the garden, I will keep it all rigid metal conduit.

The recommendation to use thwn is a good tip. I once saw a electrician pulling single conductors through metal conduit on an interior job and did not know that one can do the same for exterior runs in conduit.
I only have about 175 square feet of lawn and garden space and I will never need #12 wire. I just have a small water pump to supply a small waterfall fountain. That's the only thing that will be plugged into the receptical. If I had bigger lawn and garden, then I could get more toys to plug in and then a 20 amp circuit would make sense to me.
 
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Old 06-19-07, 08:35 PM
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argmematey writes:

If you use rigid all the way, you will have to screw the rigid into the box extender before you attach it to the wall. I don't think you can use a union coupling on electrical.
=============

yes you can but it must be an electrical union. an Erickson is what most call it:

http://www.foxelectricsupply.com/content/products/ProductDetail.asp?qsCatID=24990&qsProductNo=ARL201

if you are using this much rigid, I would simply run the entire run in rigid. I live in southern Mi and never had a problem with PVC breaking in the ground but do what you want. Philly and where I live are both the same hardiness grow zones so the temps are the same.
 
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Old 06-20-07, 03:00 PM
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I just purchase two 90 degree conduit ell's and some couplings and noticed that I can run the couplings in all the way and the male thread almost disappears into it. Are they supposed to be that loose?
I also noticed that when I tried to run another piece of conduit on the other end, it hits the other pipe thread before it gets tight.
What is it with these pipe threads?
 
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Old 06-20-07, 05:23 PM
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Conduit threads are not tapered. They are straight You are probably use to pipe threads (plumbing) which are tapered. In other words on pipe (plumbing) the diameter increases slightly as you screw it in (like a plug). On conduit it is the same diameter all the way.
 
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Old 06-20-07, 07:04 PM
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I see. But what is used to get a tight fit between couplings and the straight threads. I do not want water to enter these fittings as they will be underground. I am not sure if teflon tape will do the job
 
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Old 06-20-07, 07:07 PM
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they are not intended to be watertight. You do not want to use anything on them since they are supposed to be electrically continuous. If you put tape or sealant on the threads, you can insulate them and prevent the continuity.

simply wrench tight is what is required.
 
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Old 06-20-07, 09:42 PM
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Ok,
That settles that worry.
Today I took a good look at my front wall where some of this assembly will be mounted and decided to install pvc on the wall because part of the wall has decorative facing that would interfere with the run. To work around this interferance, I will install flexable pvc off the gfci box to rigid pvc, then another flexable pvc connector. The end of this connector will have an adapter to allow me to secure it to rigid metal conduit. This conduit will then run underground and come out in the garden using two 90 degree ells. So all of the underground connections will be rigid metal conduit.

I am also using metal boxes for the gfci box and the new box and I have a questions about bonding.
when the receptical is attached to the metal box, it is bonded by the metalwork of it; correct? The metalwork also has the grounding screw.
I am running 2 conductors with a ground wire; do I need to attach another wire to the frame of the new box and run it back or can I just attach a short piece of ground wire to the grounding terminal and the frame of the box?
 
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Old 06-21-07, 06:16 AM
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>>>I will install flexable pvc off the gfci box to rigid pvc, then another flexable pvc connector. ... This conduit will then run underground and come out in the garden using two 90 degree ells.

You don't say how much offset there will be in the flexible PVC, and I am guessing these are just traversing a surface irregularity, not changing direction, but remember code requires pull boxes or conduit bodies between bends totaling 360 degrees. I shoot for 180 degrees, but that's not always practical.

>>>I am also using metal boxes for the gfci box and the new box and I have a questions about bonding.
when the receptical is attached to the metal box, it is bonded by the metalwork of it; correct?

Yes, 2005 NEC 250.146(A) permits this as long as the metal yoke is in direct contact. "To ensure an effective ground-fault current path between the metal box and yoke, at least one of the insulating retaining washers must be removed from the receptacle." See my further notes below.

>>>The metalwork also has the grounding screw.
I am running 2 conductors with a ground wire; do I need to attach another wire to the frame of the new box and run it back or can I just attach a short piece of ground wire to the grounding terminal and the frame of the box?

The problem I have had with cast aluminum box grounds is that the tapped hole is raised off the back of the box. You may be OK with 14 AWG but getting 12 AWG in a small enough loop to fit under that screw is tough. Consider a pigtail with a lug (round "loop" if possible) to go on the box grounding screw, and then a wire nut to connect it to the ground wire coming through the conduit.

Another approach is to measure about 6 inches from the end of your ground, and at that point strip off an inch of insulation. Loop that spot on your box screw, then put the end on the receptacle.

Also although I use all self-grounding receptacles (Leviton 5200 (?) series or cheaper BR15), when outdoors I always use a grounding pigtail on these receptacles. I do not trust the ground path due to the effect of moisture on the aluminum. I also put some no-ox on the aluminum connections. But that might be a bit anal.

Two more things:

Use a 2-gang weatherproof box for the GFCI on the house if you have the space. It makes it a lot easier to jam all the wires and the GFCI in.

If there's conduit going into the house from your GFCI, make sure it's plugged with electrician's putty on both ends to keep air from flowing through. This will reduce condensation inside the conduit.
 
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Old 06-21-07, 07:01 AM
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<You don't say how much offset there will be in the flexible PVC>
The offset is about 1-1/2 inches from out of the gfci box and is in the same direction. Now the other flexable pvc will have the same offset but will be elbowed to 90 degrees.

<Consider a pigtail with a lug (round "loop" if possible) to go on the box grounding screw, and then a wire nut to connect it to the ground wire coming through the conduit.>
I will do that.

<Use a 2-gang weatherproof box for the GFCI on the house if you have the space. It makes it a lot easier to jam all the wires and the GFCI in.>
Good idea and will be implemented. Thanks.
 
 

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