NEC 2011; underground residential circuit

[nebben]

Hey all,

I have a couple of things to do before I break ground on a new garage. The first project includes burying and stubbing two electrical circuits that go to a greenhouse.

The code I need to comply with is NEC 2011. The only thing I understand is that I need to bury the lines 24" beneath the ground's surface.

Some basic questions;

• Can I bury the conduit directly in the dirt, or do I need to lay gravel in the trench above/below the conduit?
• I want to run 2x 20 amp circuits approximately 100 feet; is this just two pairs of 12/2 (with two grounds)?
• Is there a requirement for a separate ground buried beneath the outbuilding?
• How large of conduit is typical for two 20 amp circuits like this?

Thanks y'all!

 

[Mustang51js]

You can run pipe right in the ground, usually 18 inches. And you can't run romex in the pipe underground, you will need #12 thhn

 

[justsam]

I believe you may have an issue with two separate circuits if this is a detached building. You may be allowed only one circuit, and then a subpanel for local distribution. Check with how your local jurisdiction considers a greenhouse.

Use wire THWN since this is a wet location.

 

[wyliesdiesels]

As others have said, u cant run nm-b/Romex underground. U will need either UF-b or thhn wire in conduit.

And yes u may get nailed on the multiple circuits to a detached structure.

If u are just putting in one branch circuit and no subpanel, u dont need a grounding electrode/rod!

The size of conduit is dependent on wire size not circuit ampacity!

With #12 your voltage drop will be about 3.3 %, which is fine but u may want to step upto #10 if u will have any large motor loads like a saw or small compressor!

 

[Norcal]

As others have said, u cant run nm-b/Romex underground. U will need either UF-b or thhn wire in conduit.

And yes u may get nailed on the multiple circuits to a detached structure.

If u are just putting in one circuit, u dont need a grounding electrode/rod!

The size of conduit is dependent on wire size not circuit ampacity!

A multi-wire circuit counts as one circuit, and only one circuit is permitted to a outbuilding.

Edit: THHN is for dry locations only, but most is dual rated THHN, THWN, but have seen THHN only conductor...

 

[wyliesdiesels]

A multi-wire circuit counts as one circuit, and only one circuit is permitted to a outbuilding.

Yeah i didnt word that correctly. I went back and edited it.