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Old 10-28-2011, 12:09 PM   #1
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What kind of wire in underground conduit?


Hello forum,

I'm burying a schedule 40 conduit in the ground, 60 feet to a small outbuilding. What kind of wire should I run through the conduit? Single strand wires or some indoor romex I happen to have a lot of?

This question is more about general code requirements than what will work.

Thanks in advance for help.

-Tom

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Old 10-28-2011, 12:38 PM   #2
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What kind of wire in underground conduit?


Use thwn or uf cable.
Indoor romex can not be used.

What size is the pipe?

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Old 10-28-2011, 12:44 PM   #3
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What kind of wire in underground conduit?


Wire need to be wet rated. That means that somewhere in it's rating is a W, such as RW THWN or a U for underground..
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Old 10-28-2011, 01:48 PM   #4
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What kind of wire in underground conduit?


Are you running a single circuit or for a sub-panel?

There are 2 types of wire: THHN, THWN, THHN/THWN.

You CANNOT run THHN underground. If the wire is marked THHN/THWN then it can be run underground in conduit.

I remember it like this: THHN (H=high as in not buried) and THWN (W=wet as in in the ground).

I've noticed that most big box stores don't carry THWN but the "THHN" they carry is actually THHN/THWN.

John
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Old 10-28-2011, 02:59 PM   #5
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What kind of wire in underground conduit?


jbfan, I don't have the conduit yet. I'll probably get 1 inch.

Johnsteph10, yes, to a sub-panel or master on/off switch. Have not decided yet.

I have some green single strand wire marked with
"W 12 AWG VW-1 TYPE THWN (UL) 600 VOLTS Gasoline or Oil resistant or AWM"

Thanks for the responses!
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Old 10-28-2011, 05:18 PM   #6
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What kind of wire in underground conduit?


Quote:
Originally Posted by thomlep View Post
jbfan, I don't have the conduit yet. I'll probably get 1 inch.

Johnsteph10, yes, to a sub-panel or master on/off switch. Have not decided yet.

I have some green single strand wire marked with
"W 12 AWG VW-1 TYPE THWN (UL) 600 VOLTS Gasoline or Oil resistant or AWM"

Thanks for the responses!
You can not use green #12 THWN for the hot or neutral conductors, it is for the EGC (ground ) only.
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Old 10-28-2011, 08:20 PM   #7
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What kind of wire in underground conduit?


What type wire should I use for the hot and neutral?

Thanks
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Old 10-28-2011, 09:20 PM   #8
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What kind of wire in underground conduit?


You can use the thwn, white for the neutral, green for the ground and black and red for the hots. You just can't use the green for anything except the grounding conductor. Thwn is fine for everything you are planning. Tell us the circuit size (amperage) and we can advise what size wire to use.

Last edited by Missouri Bound; 10-28-2011 at 11:20 PM.
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Old 10-29-2011, 06:16 AM   #9
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What kind of wire in underground conduit?


You should consider using 1 1/2 to 2 inch PVC -
easier to pull wire through.
Also, if there are going to be bends - use "wide"(sweep) 90's.
Is the circuit going to be 110 or 220 volts?

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Old 10-29-2011, 07:22 AM   #10
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What kind of wire in underground conduit?


Quote:
Originally Posted by thomlep View Post
What type wire should I use for the hot and neutral?

Thanks

How about what size wire should I use?

You should really consider picking up an N.E.C. book or at a minimum an Ugly's book. You need to make sure you are sizing the wire properly for the load served and sizing the breaker accordingly. That will also help you determine what size conduit to use. Distance will also be a factor to consider when sizing your wire. You have depth requirements depending on what type of conduit you use and whether you are under grass, sidewalk etc. If you are supplying the building with a feeder for a sub-panel, or if you have more than one circuit running to the building, then you'll also have to install a grounding electrode.
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Old 10-29-2011, 11:38 AM   #11
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What kind of wire in underground conduit?


Thanks for your response Sine. I'm running 2 110/20 amp circuits, which is why I'm using 12 gauge wire. My questions are more about type, than size, but now I'm wondering about conduit size. The distance is 65 feet to the outbuilding from the main panel.

What is the minimum size conduit needed for these two "household" circuits.
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Old 10-29-2011, 12:14 PM   #12
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What kind of wire in underground conduit?


Quote:
Originally Posted by thomlep View Post
Thanks for your response Sine. I'm running 2 110/20 amp circuits, which is why I'm using 12 gauge wire. My questions are more about type, than size, but now I'm wondering about conduit size. The distance is 65 feet to the outbuilding from the main panel.

What is the minimum size conduit needed for these two "household" circuits.
Minimum 3/4", you could get away with 1/2" but I wouldn't it's just a pain to pull wire through. But if you think you might want to add a circuit or a switch leg down the road you may want to go a little bigger.
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Old 10-29-2011, 02:03 PM   #13
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What kind of wire in underground conduit?


Quote:
Originally Posted by thomlep View Post
'm running 2 110/20 amp circuits, which is why I'm using 12 gauge wire. My questions are more about type, than size, but now I'm wondering about conduit size. The distance is 65 feet to the outbuilding from the main panel.
You do know that you are only allowed 1 circuit to a detached building"

That 1 circuit can be a MWBC (multi wire branch circuit. A MWBC consists of 2 hots, 1 neutral and one ground. They must come off a 2 pole breaker in the house load center. A MWBC will effectively give you the 2 20 amp circuits you want.

For a 20 amp circuit at 65", #12 wire is fine. Use THWN wire for conduit.
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Old 10-29-2011, 04:07 PM   #14
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What kind of wire in underground conduit?


Quote:
Originally Posted by Sine View Post
Minimum 3/4", you could get away with 1/2" but I wouldn't it's just a pain to pull wire through. But if you think you might want to add a circuit or a switch leg down the road you may want to go a little bigger.

I consider 3/4 to be the minimum for underground. I never use 1/2 unless its under 10'. I would run a minimum 1" to an out building like this. Code says you can do 1/2 though.
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Old 10-29-2011, 04:11 PM   #15
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What kind of wire in underground conduit?


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Originally Posted by jimmy21 View Post
I consider 3/4 to be the minimum for underground. I never use 1/2 unless its under 10'. I would run a minimum 1" to an out building like this. Code says you can do 1/2 though.
So... you basically said what I said.

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