Ready to dig trench for 100A service

[VHF]

After a couple years of living with only temporary power to my detached garage, I have lined up a guy with a Kubota BX25 to dig a trench 125' from my house to the detached garage so I can run a 100A service to the garage off the 200A main panel in my house. I told him I want the trench 30" deep. In the trench will be:

1 1/2" PVC schedule 40 conduit for electrical feed to garage
1 1/2" PVC schedule 40 conduit as sleeve for a 3/4 PEX seasonal water line
1" PVC schedule 40 conduit for communications cables
Caution tape

I have a 1 1/2" PVC conduit stubbed up through the slab and into a stud bay, so I'm kind of locked into that conduit size if I want to use my existing stub-up.

I am planning to run (3) #3 CU THHN/THWN conductors plus (1) #8 CU ground in the 1 1/2" PVC conduit. I also want to run (3) #12 wires backto the house as a 3-way switch leg for the light outside my service door. Do I run into any trouble with derating or fill if I put these in the same conduit with the feeders? Would it be better if I ran a separate conduit for the switch leg wires?

Trench length is 125'. Total wire length panel-to-panel will be 140'.

Now I'll probably get about a 100 posts about how AL is much cheaper than CU (I am hoping it will drop a little before I buy the wire!) and how I should run a 2" conduit for easier pulling, but other than that am I missing anyting? Any obvious code violations or potential problems? (On 2008 NEC, no applicable local amendments.)

 

[mrobins297aaa]

Why are you running conduit for the pex pipe? are you running it the full 125' or just a stub up?

I ran my 3/4 pex and had a 2" pvc stub up into my barn and had a hard time getting that 3/4 pex thru a 3' pc and 1 90 of 2" pvc. that pex is so stiff.

I was 225' feet from my 200 amp panel and I used 3-2/0 and 1 #2 al direct buriel (I think it was use wire) to my 100 amp panel in the barn.

 

[mrb]

for the $20 or $30 it will cost, I would throw in a seperate 3/4" for your 3 way conductors. That eliminates the insulation on a smaller conductor becoming damaged by one of the larger conductors. You will need to put a ground wire in there too.

 

[VHF]

If I run a separate conduit for the 3-way switch, should I run that ground all the way to the ground screw on the 3-way switch in the house (rather than pick up a ground in the house)? In that case, once I get in the house, I could transition to NM 12/3 to run to the switch, which would be in is own plastic box. I'm assuming it is important to avoid a ground loop.

Would 1/2" schedule 40 PVC be big enough for (4) #12 THHWN/THWN wires? I know that 1/2" PVC is pretty small inside! I'm asking because I have a 1/2" stub up I could use. But I'm willing to run 3/4" if needed.

 

[Stuart in MN]

Four #12s will fit in a 1/2" conduit.

 

[mrb]

If I run a separate conduit for the 3-way switch, should I run that ground all the way to the ground screw on the 3-way switch in the house (rather than pick up a ground in the house)? In that case, once I get in the house, I could transition to NM 12/3 to run to the switch, which would be in is own plastic box. I'm assuming it is important to avoid a ground loop.

Would 1/2" schedule 40 PVC be big enough for (4) #12 THHWN/THWN wires? I know that 1/2" PVC is pretty small inside! I'm asking because I have a 1/2" stub up I could use. But I'm willing to run 3/4" if needed.

you have to run the ground with it because all circuit conductors including ground have to be run together.

 

[VHF]

Hypothetical question: Say you have a simple lighting circuit where the power runs first to a ceiling light fixture, then to a wall switch and back (a switch leg.) If that switch was in a single box by itself of course you would need to run a ground in addition to the hot and switched hot conductors (not to mention a neutral under 2011 code!)

But what if the switch was in a metal box with another switch on a different circuit and the metal box is grounded by that other circuit? Would you still need to run a ground along with the switch leg? Would you bond it in the metal box or leave it isolated?

 

[mrb]

Hypothetical question: Say you have a simple lighting circuit where the power runs first to a ceiling light fixture, then to a wall switch and back (a switch leg.) If that switch was in a single box by itself of course you would need to run a ground in addition to the hot and switched hot conductors (not to mention a neutral under 2011 code!)

But what if the switch was in a metal box with another switch on a different circuit and the metal box is grounded by that other circuit? Would you still need to run a ground along with the switch leg? Would you bond it in the metal box or leave it isolated?

you need to run a ground along with the circuit conductors. And yes you would tie it to all the other grounds in the box and bond the box.

 

[wuck]

1" PVC schedule 40 conduit for communications cables

If the com lines include CATV, telephone, or intercom, keep them as far as possible from the AC lines to reduce interference. Computer network cables (cat 5 etc) shouldn't be affected by AC (differential transmission), but . . .

Pat

 

[nate379]

Is 30" deep enough? Might want to check into that. Here it's at least 36"

 

[Frank The Plumber]

I ran a 3" sch 80 sleeve with long sweeps 120 feet for use as a water sleeve and for comm wires. I had no problem pulling a fresh roll of K water tube out there. Well it took a rope but still not bad.

 

[fsashemi]

I just got done doing the same type of project. I ran 2-2-2-4 and let me tell you it might have fit through 1-1/4" but I wouldnt want to pull it. I ran 2 inch and it was still a pain in the a**. I did have four 90's though.

 

[Aceman]

For the love of all things holy, do not run 1/2" pvc. It is the DEVIL!!

We use 3/4" as a minimum when it comes to pvc/rigid.

1.5" pvc is fine. If you only have two 90's in it along with the fact you'll probably get the new super slick wire you should have no problems. Don't let anyone tell you otherwise.

You only need 18 inches of cover on your conduit except where you cross under driveways/roads, you'll need 24 inches there. If you're at 30" then you won't have any trouble.

 

[VHF]

I'm planning to put the 1" communicaitons conduit 6" to 12" above the electrical lines to reduce interference.

I'm still waffeling on whether to come above grade at the house and use an LB to go thru the rim joist or drill through the basement wall (in which case I would only have one 90 in my pull.) Because this is the front of the house I would get points with the wife if I avoid a visible installation... if I use an LB I'll probably have to get a shrubery to hide it!

My foundation wall is 10" poured. I can rent a rotary hammer with 2" core bit. Any advice/suggestion on drilling through a poured wall? What if I hit rebar? I want to go from the outside to keep from filling the house with concrete dust!

 

[jvitez]

For the love of all things holy, do not run 1/2" pvc. It is the DEVIL!!

We use 3/4" as a minimum when it comes to pvc/rigid.

Couldn't agree more. Used 1/2" PVC conduit once, only once. Never again. 10 ft of straight conduit only costs about $2 more here for 3/4 vs 1/2 inch.

 

[Aceman]

I'm still waffeling on whether to come above grade at the house and use an LB to go thru the rim joist or drill through the basement wall (in which case I would only have one 90 in my pull.) Because this is the front of the house I would get points with the wife if I avoid a visible installation... if I use an LB I'll probably have to get a shrubery to hide it!

Going through a poured wall underground is a good way to have future water problems in your basement. You'll never get it totally sealed....

All the points you got with your wife for concealing it underground would be gone....and then some!

Plant a shrub.

 

[VHF]

With a 1-1/2" LB for power, a 1" LB for comm lines, and a 3/4" LB for my 3-way switch leg all visible on the front of the house, I better get a couple shrubs... and maybe better buy her a rose bush, too!