What's the MINIMUM depth of a trench from top of the cable/conduit to final grade? (Select two options.)

Question

Options

• A305 mm(12 in)
• B610 mm (24 in)
• C914 mm (36 in)
• D1270 mm (50 in)
• EBelow the area's 50-year frost line

• A
  10% (6)
• B
  73% (46)
• C
  14% (9)
• D
  3% (2)

Explanation

For most direct-burial cable and conduit installations, 610 mm (24 in.) is the standard minimum cover depth required by codes like the NEC (Table 300.5), protecting cables from routine digging, foot traffic, and mechanical damage. In cold-climate regions, that 24-inch minimum alone isn't enough - burial must go below the 50-year frost line to prevent frost heave from shifting or cracking cables and conduit. Together, B and E capture both the universal baseline and the climate-specific override that applies wherever frost depth exceeds 24 inches.

Why the others are wrong:

• A (305 mm/12 in.) is too shallow for general cable/conduit burial; it may appear in limited exceptions (e.g., GFCI-protected residential branch circuits under concrete slabs), but is not the general minimum.
• C (914 mm/36 in.) and D (1270 mm/50 in.) exceed the minimum requirement - these depths aren't wrong to use, but they aren't the minimum, which is what the question asks.

Memory tip: Think "2 feet or freeze" - the baseline is 2 feet (24 in./610 mm), but if frost goes deeper, you follow the frost. That covers both correct answers every time.

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