Corrosion protection is a BIG "if." That said.... and bear with me, I am going by practical experience and NOT code here...these would be my "EMT rules:"
1) First foot into ground gets pipe wrap; 2) Passing under sidewalk or slab, at least 4" below either (so the concrete saw misses it); 3) Area totally unsuitable for walking over, due to landscaping, etc,... at least below the irrigation pipes; and 4) Under anything even vaguely resembling a road or parking lot, 2 ft!; and, finally- 5) Always totally inadequate for supporting any box, anywhere. Better make a frame from strut.
I have never seen EMT corrosion protection I "judged suitable for the condition." of being buried in Florida. I have dug up EMT that was in the ground less than 5 years and it was a rusty trail of sand with THWN in it. The only reason you would know it was EMT was the zinc connectors. We do have pretty salty ground water tho, typically 5 PPT or so, west of 41.
Re: Burial Depth#98909 06/23/0610:24 AM06/23/0610:24 AM
(A) Exposed and Concealed. The use of EMT shall be permitted for both exposed and concealed work.
(B) Corrosion Protection. Ferrous or nonferrous EMT, elbows, couplings, and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition.
(C) Wet Locations. All supports, bolts, straps, screws, and so forth shall be of corrosion-resistant materials or protected against corrosion by corrosion-resistant materials.
Where does it say anything about having to be buried? I can be run along the top of the ground if it is suitable for the condition. Like where outside wall or foundation meets the finished grade. Maybe 1/2" lower if you don't want it visible.
Now if you'll tell us what this is being used for maybe we can provide a good answer.
George, I would say Table 300.5 column 3 or 4 depending on the location, and that all other 300.5 requirements are met. This link also provides some info re the subject of corrosion protection for EMT: http://www.steelconduit.org/pdf/ConGuide.pdf
dlhoule--You make a very good point, but you cannot bury anything a half inch below the ground. Once something is 'direct-buried' (as opposed to indirect-buried) 300.5(A) kicks in and the appropriate depth for the situation kicks in. Unless under a building, the minimum depth would be 4".
What makes me wonder is that service conductors that are buried less than 18" below grade do not need a warning ribbon, but 18" or more does. What sense does that make? 300.5(D)--Protect the person digging a large hole, but the poor gardener can get fried?