Question about direct buried cable running to shed

[Marcus Waddell]

Hey all,
I need to run a 8/3 UF cable from my main panel in the house to my shed. Total distance is about 120 ft away, so for a 20A circuit that requires 8/3 cable. My question is this. The Table 300.5 in the NEC says 24" deep if using Column 1, but Column 4 says if it's a 20A GFCI protected circuit then you only need to bury 12". Since I'd still be using UF cable, do I need to follow Column 1 (24" deep) or Column 4 (12" deep). Thanks in advance.

FYI, this is just for a few outlets and a couple of LED lights in my 12x16 shed. Only 60ish feet is outdoor, the balance is the run from the inside panel box to outside.

 

[Stuff]

Why 8 gauge wire? Most would go with 12 if just a few lights. Put it on a 15 amp breaker if that makes you feel better.

Is this 8/3 with ground (4 wires total with a double pole breaker) or 18/2 with ground (3 wires total - hot, neutral, ground)? Most inspectors will want the first at column 1. If 2nd one (single pole breaker) you can do the 12" depth with a GFCI breaker or GFCI receptacle before it gets buried.

 

[Sponsor]

 

[Marcus Waddell]

It's 8/3 with ground (4 total wires) but a single pole GFCI breaker.

 

[Kreemoweet]

The wiring method you use is irrelevant, if it is a 120V branch circuit with GFCI protection and a maximum 20A-rated breaker.
It would qualify for the 12" cover depth. Depending on your particular circumstances, it may still be better to go deeper. Stuff happens,
especially if there are children involved. Or gardeners.

My version of NEC has a Note #4. at the bottom of that table which is directly relevant.

 

[Marcus Waddell]

I supposed I should have read all the notes at the bottom of the table. Thanks for the heads up.

 

[Marcus Waddell]

Why 8 gauge wire? Most would go with 12 if just a few lights. Put it on a 15 amp breaker if that makes you feel better.

Is this 8/3 with ground (4 wires total with a double pole breaker) or 18/2 with ground (3 wires total - hot, neutral, ground)? Most inspectors will want the first at column 1. If 2nd one (single pole breaker) you can do the 12" depth with a GFCI breaker or GFCI receptacle before it gets buried.

Why 8 gauge? It's a 120 ft run and for a 20A circuit, that is what is required to stay below a 3% voltage drop.

 

[Stuff]

Why 8 gauge? It's a 120 ft run and for a 20A circuit, that is what is required to stay below a 3% voltage drop.

That's fine with a big budget government contract but in the real world a bit of voltage drop is fine. How often are you going to have a full 20 amp load on the circuit? Even then what do you have that is sensitive to the drop?

 

[Marcus Waddell]

That's fine with a big budget government contract but in the real world a bit of voltage drop is fine. How often are you going to have a full 20 amp load on the circuit? Even then what do you have that is sensitive to the drop?

Will likely be running some tools with motors from time to time, so that is definitely a concern.

 

[Marcus Waddell]

Another question for the group. Running 8 gauge to shed due to distance, but the outlets will need to be 12 gauge. When I transition from 8 to 12 gauge, do I use a wire nut or a butt splice? (Obviously in a box, not out in the open).

 

[Stuff]

A wire nut is usually easier than a butt splice, even with 8 gauge wire.

Note that before going to any outlet your feeder needs to go to a disconnect. Can be a simple wall switch. Some use a disconnect box or even a panel as then you have a good place to transition between cable sizes.

 

[Marcus Waddell]

A wire nut is usually easier than a butt splice, even with 8 gauge wire.

Note that before going to any outlet your feeder needs to go to a disconnect. Can be a simple wall switch. Some use a disconnect box or even a panel as then you have a good place to transition between cable sizes.

That is the idea. Since a switch wouldn't take 8 gauge wire, I need to transition to 12 gauge somewhere and the disconnect (aka switch) would be a great place to do that. Unless I am totally misunderstanding the reasoning for the purpose of that switch.

 

[Reach4]

For not a lot more money, you could put in a sub panel fed by your 8 AWG. Run 2 hots and a neutral and ground. Then you could have a 240 outlet for your new welder etc. Have 2 or more circuits for outlets.

Not saying you need that, but its easier now.

 

[Marcus Waddell]

For not a lot more money, you could put in a sub panel fed by your 8 AWG. Run 2 hots and a neutral and ground. Then you could have a 240 outlet for your new welder etc. Have 2 or more circuits for outlets.

Not saying you need that, but its easier now.

Only issue with that is I would have to dig to 24 inches, instead of 12. Here in Georgia, this is problematic.

 

[Reach4]

Only issue with that is I would have to dig to 24 inches, instead of 12. Here in Georgia, this is problematic.

Could you use a sidewalk going that way? If you laid a sidewalk on top, the burial depth becomes 6 inches if I read correctly. I don't know if that is 6 inches below the concrete, or 6 inches below ground level, or what.

If you used rigid metal conduit, the depth could also be 6 inches.

For schedule 80 PVC conduit? I don't know.

If the problem is clay, rather than rock, renting a trencher should make 24 inches easy enough. You would want to catch the clay on some cheap tarps, because you don't want clay in the top 4 inches when you bury... if you care about grass. Fill most of the clay into the hole, and top off with topsoil.

 

[Marcus Waddell]

Could you use a sidewalk going that way? If you laid a sidewalk on top, the burial depth becomes 6 inches if I read correctly. I don't know if that is 6 inches below the concrete, or 6 inches below ground level, or what.

If you used rigid metal conduit, the depth could also be 6 inches.

For schedule 80 PVC conduit? I don't know.

If the problem is clay, rather than rock, renting a trencher should make 24 inches easy enough. You would want to catch the clay on some cheap tarps, because you don't want clay in the top 4 inches when you bury... if you care about grass. Fill most of the clay into the hole, and top off with topsoil.

Nah, goes up hill to the shed, so no walkway.

 

[Reach4]

If you make a trench, you could add a water line. Pretty soon you will be listing your shed on AirBnB.

 

[Marcus Waddell]

If you make a trench, you could add a water line. Pretty soon you will be listing your shed on AirBnB.

LOL