In a computer or control room where the plenum is used for heating, ventilating, and air- conditioning, the finished floor height should be a minimum of how many inches?

Question

Options

• A8 inches.
• B12 inches.
• C2 inches.
• D6 inches.

• A
  6% (2)
• B
  81% (26)
• C
  3% (1)
• D
  9% (3)

Explanation

Option B (12 inches) is correct because the National Electrical Code (NEC) Article 645 specifies that in information technology equipment rooms where the raised floor space serves as the air plenum for HVAC, the floor must be elevated a minimum of 12 inches. This clearance ensures adequate airflow distribution, space for cable management, and safe access to wiring beneath the floor.

Why the distractors are wrong:

• A (8 inches) - too shallow to meet code; would restrict airflow and make cable access difficult.
• C (2 inches) - far too low; this is essentially no raised floor at all and would serve no functional purpose as a plenum.
• D (6 inches) - a common wrong answer since 6 inches feels reasonable, but it doesn't meet the 12-inch code minimum for plenum use.

Memory tip: Think "12 inches = 1 foot = room to breathe" - a full foot of clearance gives the plenum enough height to breathe (circulate air) and work (access cables). If you associate 12 with "a foot of fresh air," it's hard to confuse it with the smaller distractors.

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