Modular Data Centers practice questions

Correct: B — When the equipment is over 1.8 m (6 ft) wide or deep

646.19 requires an entrance and egress at each end of the working space for equipment over 1.8 m (6 ft) wide or deep. Voltage level, dwelling occupancy, and indoor/outdoor location aren't the triggering conditions in this section.

Correct: D — Only if the emergency lighting system is a backup type where solely the lighting shifts to battery power during a power failure

646.17 permits other equipment on an emergency lighting circuit only when the system is a backup type where under power failure only the lighting is supplied by battery circuits — device listing and room location don't matter, and the rule isn't an absolute never.

Correct: B — Articles 800 and 805

Per 646.3(F), Parts I through V of Articles 800 and 805 apply to communications wires, cables, and equipment installed in an MDC. Articles 800 and 820 is the pairing for CATV systems under 646.3(G), not communications wiring.

Correct: B — In accordance with any instructions or limitations included in the listing

646.14 requires installation and use in accordance with any instructions or limitations included in the listing itself — not warranty terms, field custom, or original design specs that conflict with the listing.

Correct: D — It must not be less than the available fault current of the service

646.7(A) ties the service equipment's SCCR directly to the available fault current of the service it connects to. Coordination with a powering module under 110.10 is the rule for 646.7(C) enclosures fed from a separate MDC system enclosure, not for direct service connections.

Correct: A — Parts I through XIV, the full article

646.3(I) states MDC lighting must be installed 'in accordance with Parts I through XIV of Article 410' — the entire article, not a subset. Limiting it to only the early general parts or only the later special-provisions parts leaves out sections of Article 410 that still apply.

Correct: A — Parts I and II

646.10 specifically requires compliance with Article 110 Parts I and II (general requirements, and installations 1000 volts or less). Part III covers installations over 1000 volts and isn't referenced by 646.10, and Part I alone would omit the voltage-specific installation rules that also apply.

Correct: D — The MDC must be marked "OVERCURRENT PROTECTION PROVIDED AT MDC SUPPLY TERMINALS"

646.6(B)(2) requires the MDC be marked "OVERCURRENT PROTECTION PROVIDED AT MDC SUPPLY TERMINALS" when protection is furnished under the 240.21 tap/feeder path. The 230.90-230.95 requirement instead applies to the separate service-conductor path under 646.6(B)(1). Multiple parallel breakers aren't permitted — 646.6(B)(2) requires a single circuit breaker or set of fuses, not two.

Correct: A — Messenger-supported wiring

646.3(K)(2) lists messenger-supported wiring (Article 396) as a prohibited method. Chapter 3 methods are the default permitted approach, fiber optic cable per Article 770 Part V is explicitly allowed, and raised-floor wiring is allowed when 645.5(E) and 645.4 conditions are satisfied.

Correct: A — At the outer edge of the battery rack

646.21 states working space is measured from the edges of the battery racks, cabinets, or trays — treating the rack as the boundary, not the room's wall, an individual cell's terminal, or the disconnect location.

Correct: B — The area is not required to comply with the 646.19 workspace requirements

Per 646.20(A), 24 volts dc is below the 60 volts dc threshold for low-voltage circuits, so this area is exempt from the 646.19 workspace requirements. The threshold is not about whether ITE is present elsewhere in the cabinet — it's about the voltage of the specific parts exposed during that servicing.

Correct: D — 646.15

646.15 requires illumination of exit access/discharge workspaces arranged so no single lighting-unit failure causes total loss of light. 646.16 addresses emergency lighting (a backup power source), not the arrangement of normal general illumination, and 646.19 covers unobstructed egress/working space clearances, not lighting.

Correct: A — 646.3(M)

646.3(M) is the disconnecting means rule requiring an approved means to disconnect MDC electronic equipment power (per 645.10) and a similar approved means for dedicated HVAC systems that also closes required fire/smoke dampers. 646.3(A) only addresses spread of fire/products of combustion through the space, not a disconnect requirement, and 646.3(E) covers fire alarm equipment, not HVAC shutdown/damper closure.

Correct: A — Parts I, II, and III

646.3(E) applies Parts I, II, and III of Article 760 to fire alarm systems, cables, and equipment in an MDC. Part IV (listing requirements) is referenced separately in 646.3(E) for cable listing, not as one of the applied installation parts — so 'all parts including Part IV' misstates the rule.

Correct: A — The environmentally controlled working aisles and equipment areas

646.3(B) states that environmentally controlled working spaces, aisles, and equipment areas in an MDC are not considered a plenum. A ceiling return-air space, an underfloor air-distribution space, and any duct-connected air-handling space are the kinds of areas the plenum wiring rules in 646.3(B) are written for.

Correct: D — 646.9(C)

646.9(C) requires flexible power cords/cables to be listed for extra-hard usage, and when used outdoors, also listed for wet locations and sunlight resistant. 646.9(A) only addresses where such cords are permitted to be used, not their listing/marking requirements, and 646.9(D) covers single-conductor cable sizing, not listing.