450 mm. if it is not being driven on. Under the cement slab it requires at least 50 mm. of concrete above it,these depths are to the top of the conduit so dig the trench at least 2 inches deeper for the thickness of the conduit.
Raceways shall be permitted to be installed directly beneath a concrete slab at grade level, provided that the concrete slab is not less than a nominal 100 mm in thickness, the location is adequately marked, and the raceway will not be subject to damage during or after installations.
If you don't like that one then Table 53 states 450mm. The concrete slab (floor) is not considered mechanical protection because it is part of the installation; that is why para (8) is there. You could go 300mm if you add mechanical protection, then the concrete.
Thanks Navyguy.I like para 8 below the concrete. With the frozen ground it will be hard enough to get it down just a few inches.
I was sceptical because an inspector recently told a contractor friend that 12" (300mm) was required under the concrete garage floor.
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