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I've been searching for information on how to bring electrical service underground to a shed that will be sitting on a concrete slab 12" thick at the perimeter. The shed will sit about 6" in from the edge of the slab. There is plenty of information available on how to run underground conduits but I'm specifically interested in how the conduit passes through the concrete slab so that it is code-compliant (US Uniform Code) and how to prepare for this before the concrete is poured.

Electrical Metallic Tubing can be buried 6" deep. Can EMT that has been bent into an L exit the face of the slab and connect there to EMT coming from the house, and emerge from the slab inside the shed just beyond the sill plate? Or does the EMT have to emerge outside the shed and connect there to a box and from that box pass through the wall of the shed?

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    Can you explain the statement EMT can be buried 6” deep. If you are thinking only 6” is required this is for rigid and IMC not EMT. – Ed Beal May 24 at 18:43
  • I have seen many statements (websites, This Old House videos, etc) that galvanized conduit can be buried a minimum of 6" deep while PVC has to be 18". I thought EMT was galvanized. – mr blint May 24 at 19:57
  • Since you haven't poured yet, please - install an Ufer ground. The 6" cover rule does not apply to galvanized conduit, only to IMC and RMC conduit types. That is straight from NEC, which is clear on this point. Being galvanized or not doesn't have anything to do with it. – Harper - Reinstate Monica May 24 at 20:42
  • @Harper-ReinstateMonica I had not heard of the Ufer. Is that type of grounding mandated for accessory buildings, like a garden shed, if the shed gets its power from a panel in the house? – mr blint May 25 at 12:00
  • Nevermind. It's just an opportunity to learn something and save yourself money and do a better job with your project. But yes, you WILL need a local GES at the shed, what kind is up to you. And a ground wire from the house. Both. – Harper - Reinstate Monica May 25 at 18:45
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If you decide to use EMT in ground it will need to be buried 18” per NEC table 300.5.

You can bring the EMT up through the slab and bottom plate if you want . I bring conduit into buildings this way quite often. Make sure to allow for your disconnect many jurisdictions require it on the exterior of the structure. You can bring the conduit up just outside the structure.

EMT coming through concrete is ok per NEC 358.10.B.1

My recommendation would be to run pvc underground and schedule 80 when you come up through the slab if not inside a wall, inside a wall schedule 40. why pvc? Emt even though it is galvanized will rust out and EMT / concrete / earth although allowed sets up the ideal conditions to rust out so it will not last as long as PVC. I have had rigid that I installed rust out but I have been doing this since the 70’s.

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  • I was hoping to avoid digging to 18" because of tree roots crossing the most direct path to the shed; at 6" depth I can avoid them. My understanding is that the cumulative degree of turns cannot exceed 360. Is that right? – mr blint May 24 at 20:00
  • I see that EMT can be galvanized but it is thin-walled. I would use the rigid metal conduit. Does that also rust out quickly? – mr blint May 24 at 20:05
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    Most emt or all the emt I have used is galvanized however if you want to use the 6” depth the table specifications is for Intermediate or rigid. Rigid will last 30 years if the threaded ends are coated as code requires but most don’t do it so it rusts out at the coupling in 25 in some areas. Yes the max bends is 360 degreee but there is nothing stopping you from adding a pull box in ground and that allows another 360. – Ed Beal May 24 at 20:29
  • If I can find one of these mini-trenchers for rent locally, the PVC approach you recommended would probably be feasible. youtube.com/watch?v=0hg04CmggTM – mr blint May 25 at 12:08

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