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Old 06-07-2012, 09:17 AM   #1
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Underground Wiring


I've finally settled on using pvc for a 30' run from my house to a shed. It will be 18" deep, be 3/4", and have 3 conductors + ground, all THWN solid (I have not liked working with stranded, can't seem to wire nut it properly).

1. Will I need to have the warning tape over the pipe location?
2. I plan on coming up through the floor of the shed straight into a load center panel. Is this okay or do I need to come up outside, have a Type LB conduit body and go through the wall?
3. If coming straight up into the panel is that good enough for wire pulling, or will I need to put some kind of device in the vertical run like a Type T conduit body?
4. Rather than pulling individual wires, would 12/3 UF work as long as my fill is less than 40%? Might be easier, as I would have it in there as I assemble.

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Old 06-07-2012, 09:58 AM   #2
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Originally Posted by smata67 View Post
I've finally settled on using pvc for a 30' run from my house to a shed. It will be 18" deep, be 3/4", and have 3 conductors + ground, all THWN solid (I have not liked working with stranded, can't seem to wire nut it properly).
Twist strands before you terminate

Quote:
1. Will I need to have the warning tape over the pipe location?
No, but it is a good idea-I do it.

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2. I plan on coming up through the floor of the shed straight into a load center panel. Is this okay or do I need to come up outside, have a Type LB conduit body and go through the wall?
Conduit body not needed. Schedule 80 for this part of run if exposed and subject to damage.

Quote:
3. If coming straight up into the panel is that good enough for wire pulling, or will I need to put some kind of device in the vertical run like a Type T conduit body?
Conduit body not needed.

Quote:
4. Rather than pulling individual wires, would 12/3 UF work as long as my fill is less than 40%? Might be easier, as I would have it in there as I assemble.
UF is fine, for 1 cable fill is 53%.


What size circuit are you running? #12/3 sounds like a 20A MWBC, yet you mention panel?

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Old 06-07-2012, 10:51 AM   #3
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Underground Wiring


Anytime you dig a trench, make sure you put something in the trench you will be glad you put in the trench years from now. UF cable is not something I would use and I highly discourage this. Lay PVC conduit in the trench double the size you actually need. That's just me and how I would do it.
I would come up through the floor like you plan and do. Straight up into the panel.
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Old 06-07-2012, 01:46 PM   #4
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Maybe I wasn't clear, but I would put the UF 12/3 in sch 80 pvc, I just think it will be easier to put in. I guess you are saying it is 53% fill in a 3/4" conduit? I'll verify. Will probably go with the 1" anyway. I am running 12/3 to a load center, I want a set of breakers in the shed. I have a second 20A 2P GFCI breaker at the main source panel. The outlets are also fed from a 20A GFCI in the shed, hopefully that or the breaker in the load center would trip first in event of a mishap, save me a trip back into the house. The load center and 20A 2P breaker were only $30.
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Old 06-07-2012, 02:21 PM   #5
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Originally Posted by smata67 View Post
Maybe I wasn't clear, but I would put the UF 12/3 in sch 80 pvc, I just think it will be easier to put in. I guess you are saying it is 53% fill in a 3/4" conduit? I'll verify. Will probably go with the 1" anyway. I am running 12/3 to a load center, I want a set of breakers in the shed. I have a second 20A 2P GFCI breaker at the main source panel. The outlets are also fed from a 20A GFCI in the shed, hopefully that or the breaker in the load center would trip first in event of a mishap, save me a trip back into the house. The load center and 20A 2P breaker were only $30.
12/3+g in a 3/4" is fine.

Double GFCI protection not necessary.

53% is what you base you conduit fill on, not 40% for one cable. Chapter 9, Table 1, note 9.

(9) A multiconductor cable or flexible cord of two or more
conductors shall be treated as a single conductor for
calculating percentage conduit fill area. For cables that
have elliptical cross sections, the cross-sectional area
calculation shall be based on using the major diameter
of the ellipse as a circle diameter
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Old 06-07-2012, 03:14 PM   #6
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Originally Posted by smata67 View Post
I have a second 20A 2P GFCI breaker at the main source panel. The outlets are also fed from a 20A GFCI in the shed, hopefully that or the breaker in the load center would trip first in event of a mishap, save me a trip back into the house. The load center and 20A 2P breaker were only $30.
Cascading GFCI devices is not a good idea. You can press the test button on the downstream device yet the upstream device will trip. It can make for a very confussing operation. 2P GFCI breakers ($150-200) are also very expensive compared to GFCI receptacles ($10 each) so you can save some $$$ buy going 2P regular breaker out to shed, then a sub panel if you wish, regular breakers there to GFCI receptacle. The only down side here is the cable in the conduit and trench isn't GFCI protected but you might be annoyed with nuicance tripping of a GFCI breaker feed to underground cables anyway.

Also if the breakers at the main panel and in the shed are the same ampacity you might get disappointing results as well. If the point of the breaker in the shed was to allow easy resetting locally bear in mind that breakers are not calibrated exactly the same. One will trip before the other. Just because you have one close doesn't mean it will trip first if the are the same ampacity. You might find the main panel breakers always trip before the local ones...

Last edited by curiousB; 06-07-2012 at 03:19 PM.
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Old 06-07-2012, 05:29 PM   #7
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Underground Wiring


I got a used 20A 2P GFCI breaker for my panel for $40. If it becomes a problem, the non-GFCI ones are relatively inexpensive. I understand the GFCI units may not coordinate, the one in the main panel may trip first, I guess I could run a test.

Is it okay to also run coax along with the power in the underground conduit? Does the code care? I may want cable TV in my shed!
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Old 06-07-2012, 05:34 PM   #8
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Is it okay to also run coax along with the power in the underground conduit? Does the code care? I may want cable TV in my shed!

You will need to install a separate conduit for the cable tv it's not a good idea to have it with the power wires and code does not allow it.

Also you will want coax rated for direct burial so it will last.
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Old 06-07-2012, 07:09 PM   #9
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You will need to install a separate conduit for the cable tv it's not a good idea to have it with the power wires and code does not allow it.
I just asked that same question in another thread and Code05 said it's fine as long as the cable tv and power wires are in separate conduits.

Why is it not a good idea to have it with the power wires?
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Old 06-07-2012, 09:54 PM   #10
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Inductive coupling of power into coax. Will create other problems. Also code forbids mixing such services in a common conduit. If you use underground grade coax it doesn't need conduit. Put in power conduit and backfill a few inches they lay in coax and complete backfill. Maybe warning tape over coax noting cables below...

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