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Old 08-26-2006, 09:14 PM   #1
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ruducing pipe size, Legal?


Hi, Is it legal to reduce the size of PVC conduit down in the run as long as the smaller size is still within the 40% fill?

Im running 1" PVC for my 6-4GA THWN wire, I already have a hole in my concrete block foundation that is just large enough for the flanged (Bell End) of a 3/4" pull elbow to fit thru.

So I was gonna run 3/4" out of the house, transisition over to 1" and run that 1" underground and into the sub panel in my Garage. The 1" in the ground will make it much easier to pull, rather than doing 3/4" the whole run.

Thanks in Advance...

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Old 08-27-2006, 10:08 AM   #2
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ruducing pipe size, Legal?


I have looked in the past, and I have never been able to find a code statement prohibiting what you are suggesting. It certainly would be ok at a pull point like an LB. The problem you are going to have is finding a fitting that will do what you want. Unlike plumbing, electrical pvc has a limited number of different configurations of conduit size changeing fittings.

I am thinking a 1 inch LB at the house mounted on a bracket that will allow it to stand off the wall, (uni strut is a good way to go.) Then use a reducer in the LB and run 3/4 conduit into the house. You can then run 1 inch out the bottom.

Or you could buy a 6x6x4 plastic box. and make the change in it, but you would need the correct size hole saws or drill bitts for the conduit entry holes. Trade size (the name we use) does not equal actual drill bitt size.

I am however not clear on how many of what size wire you are pulling. 6 each number 4 will not fit in a 3/4. You need 1 1/4 for those.


Last edited by jwhite; 08-27-2006 at 10:13 AM.
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Old 08-27-2006, 01:48 PM   #3
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ruducing pipe size, Legal?


Thanks JWhite, Silly me typed 4 ga, actually I will be running (3) 6GA, and (1) 10 GA for my ground back to the main panel (60 Amp Over Current Breaker). My primary 6 GA ground will connect to a ground rod out side the garage.

I think if I come up the corner of the house to an LL, and use a reducing coupler on on end, and come out of there with my 3/4" and over a few feet to a 90 deg Pull Elbow, where my hole is the foundation.

Thanks for your help
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Old 08-27-2006, 02:10 PM   #4
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ruducing pipe size, Legal?


Ok the number six wire clears up the conduit size issue.

Now lets talk about the primary ground comment.

To feed a sub panel in the manner you are talking about you need two hots, one neutral, and one ground.

At the main panel, if it is actually a main panel. The two hots go on the breaker. The neutral and ground go to the neutral/ground buss.

At the sub panel in the out building, the two hot wires need to land on a main breaker or some other disconnect means. The neutral needs to land on an isolated neutral bar. (isolated from ground). The ground wire needs to land on a ground bar that is bonded to the enclosure and the requred ground rod.

This will sound strange, but the wire to the ground rod needs to be number 6. Remember its purpose is for something like a lightning strike, not a line to ground fault like the number 10 that goes back, eventually to the transformer.
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Old 08-27-2006, 02:26 PM   #5
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ruducing pipe size, Legal?


yes, I have a Square D 100 amp main breaker panel, that has a screw that can be removed to allow it to work as a sub panel (isolate the grounds and Neutrals)

I will feed the sub panel with 6-3 W Ground NM (romex) off a double 60amp breaker, to a Junction box, in the Junction box I will transisiton over to PVC, and splice over to THWN wire (3) 6 GA (Black, Red, White) and (1) 10 GA Ground out thru the conduit and into my sub panel.

Since I will also have a metal conductor path back to the house in seperate conduit will run a low voltage 2 conductor wire that will connector to the alarm system, and a direct burial cat 5E Cable.

the 10ga ground going back to the main panel will act like a bond right, in case a neutral wire were too come loose? while the main ground is the 6 GA going to the ground rod outside the out building??

Last edited by stagger19; 08-27-2006 at 02:41 PM.
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Old 08-27-2006, 04:30 PM   #6
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ruducing pipe size, Legal?


Just removing that screw will not seperate the ground and neutral bar. The tie bar between the two also needs removed. With some panels you will need to purchase a seperate ground bar and install it.

The number 10 going back to the house is your main ground. The number six to the rod is your supplemental ground rod.

Grounding and bonding is one of the most confusing parts of the code to understand. This one chapeter of the code gets more traiing classes generated than the other nine chapters combined.

Last edited by jwhite; 08-27-2006 at 04:36 PM.
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Old 08-27-2006, 06:17 PM   #7
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ruducing pipe size, Legal?


You had me curious, so after reading your post, I went to check my panel (its not terminated yet) With the screw in place, I used my multi meter set to continunity mode, and naturally I was getting a closed circuit between the ground bus bar that I installed, and the neutral bar. I removed the screw, and that did isolate them. Apparantly this panels design only uses a screw that goes thru the neutral bar and into the box cabinet to tie the 2 together. I know a lot of them use a tie bar.

Thanks for all your help.

Now If I can only get the rains to stop, I can run the pipe. My 20" deep trench that I dug is half full of water, and more like a stream Now. LOL!


Last edited by stagger19; 08-27-2006 at 06:20 PM.
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