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Running Power to an out building


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2024 Aug 11, 6:15am   124 views  8 comments

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I know there is at least one electrician amongst the PatNetters. I am not, but I do have a question pertaining the interpretation of NEC code table 300.5.

I've asked a couple of local licensed electricans' and have not gotten a decisive answer (meaning I have not gotten the answer I wanted).

I am going to be running power from the main house circuit panel to an out building with a run of approximately 150 feet.

My question involves the burial depth for 2 inch conduit with THHN conductors to support a 40 or 50 A service to a subpanel in the out building.

Because the burial involves going through clay soil and through a dead tree root system I would like to keep it as shallow as code allows. I do not want to deal with metallic conductor because PITA. I do not want to deal with direct burial cable because PITA. I want THHN in plastic conduit because NPITA.

By my interpretation that means I'm looking at column Column 3 of table 300.5 : "non-metallic raceways etc..."

My question is this : If I dig the trench 4 inches wide at a depth of 14 inches (12 inch depth + 2 inches for conduit) and then fill it in with bags of Quickrete do I meet the requirements as stated in column 3, row 2 which states " In trench below 50mm (2 in.) thick concrete or equivalent" ? My local elec's are telling me to dig it to 20 inches but without addressing what is in the table itself - because no one has asked them about filling the trench with cement before so they aren't sure.

TIA.

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1   HeadSet   2024 Aug 11, 7:38am  

stfu says

If I dig the trench 4 inches wide at a depth of 14 inches (12 inch depth + 2 inches for conduit)

Around here, wire in PVC/plastic conduit must be buried at least 18 inches deep, even if it runs under a driveway. Actually, it does not matter what Patnet thinks or even what your local electricians say. What matters is what your local inspector will approve. You may want to just call and ask if he would approve a 12 in depth if covered in concrete. I am not an electrician, but I have wired houses I bought and restored, even one where I ran a cable from a main panel to install a 50 AMP panel in a detached garage. I passed all inspections.
2   WookieMan   2024 Aug 11, 7:40am  

I don't know code and don't care to look it up. Put it in whatever conduit suitable for underground and just do it. 14" or 14' who cares. I think the concrete idea is overkill. As long as you mark where it is, it shouldn't be a problem. Disclose it when you sell.

We just filled in our pool and there were a couple of lines in the ground. Low voltage stuff and not to other people's homes. If you hit a 50A line with a skid steer or excavator you're not going to die. A shovel won't break PVC conduit. It will just trip the breaker in the main house if you hit it hard enough to break it. I wouldn't overthink it if you're not pulling permits.

If you are, I'd just hire someone.
3   HeadSet   2024 Aug 11, 8:02am  

I hope you can take a joke, WookieMan, but your post reminds me of this Canderville character:


4   Tenpoundbass   2024 Aug 11, 8:59am  

Don't fill the trench with concrete. Building a slab over it is OK, but you don't want PVC buried and encased in concrete.
You said you have hard tough clay, that isn't going anywhere. I dug my shed trench in sugar sand, and will always know where it is, if ever need to dig there. Which I doubt. The line isn't anywhere I would want to dig a deep hole to plant a tree or some construction plans.

I would also try to run a 60 amp circuit to your Shed. Also install a 240V Mini Split, they are more efficient and cool much better than a 120V Mini Split.
I have the 240V in my shed, it gets so frosty my toes get numb. The 120V minis in the back additions on my house, never cool as fast or as cold.
Also try your best to make it as much to code as possible, if you're not sure then ask someone. If you get busted by the City, if it's done right, then all you will have to do is a bunch of paperwork and pay fines and fees, if it's done right. If it's not you will have to also pay those fees and fines but take it all out. All outlets must be within 6 feet of each other. I would use number 12 wire and every circuit on 20 amps. You never know if someone in the future will be running shop tools in there.
I don't know if you're going to finish the walls and ceiling with drywall or not. But if you are I would run some number 14 wire for 15amp lighting circuits. In the future if you want to install recessed lighting it will be there.

The mini split is a double 20 and so is every outlet, so I went with a 60 amp circuit to my shed. So ran number 4 wire in my pipe.


The white romex in the ceiling is for recessed lighting in the future. I still haven't installed it yet, but it's there.
Right now it's a music room, but eventually I want to make it a real shop for fabrication and tinkering. I will want to light it up very well at that point.
All I will need to do is cut out a 4" holes and cut the loop and put in the drivers and pop in the wafer light.


Another final thought is also don't forget to run another pipe out to the she for low voltage and communication lines. You'll want to keep that from the power pipe at least 6 inches from the low voltage pipe. WiFi from the house will be spotty and terrible. So you will want a Cat 6 cable ran out to the shed, and if you have an alarm in the house, you can also run alarm wire, so your shed will be protected from Democrat voters.
5   Tenpoundbass   2024 Aug 11, 9:59am  

On further thought, I would not encase the pipes in concrete. If the concrete settles and cracks it will crack the pipe along with it. Then your wires will be exposed to the dirt and water. Even if it does no harm to the wire, pulling old wires out or new wires in, will be impossible.
6   HeadSet   2024 Aug 11, 1:01pm  

Tenpoundbass says

install a 240V Mini Split, they are more efficient and cool much better than a 120V Mini Split.

Good to know, thanks. I am considering renovating an old 1950s built house with mini splits instead of a central air system.
7   stfu   2024 Aug 11, 5:48pm  

Tenpoundbass says

On further thought, I would not encase the pipes in concrete. If the concrete settles and cracks it will crack the pipe along with it. Then your wires will be exposed to the dirt and water

Thanks for this - it had not occurred to me. I'll attempt to get down to 20 inches with a trencher but about 8 linear feet has to be dug by hand. I'll be running a separate conduit for the data (CAT) cable about 1/2 way into the trench depth.

So you ran 4 AWG THHN through conduit for your shed? The conduit in your pix looks like 1/2 inch - I'm surprised you got the wires through it. Can you confirm sizes?
8   Tenpoundbass   2024 Aug 12, 6:06am  

On the left you see 1/2 inch the other two are 3/4.

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