Remote disconnecting means for IT equipment rooms
NEC 645.10 A single grouped, identified remote disconnect must be able to cut power to electronic equipment and dedicated HVAC and close fire/smoke dampers, reachable by responders during a fire.
Q1 NEC 645.10
Where must the remote disconnect controls for an information technology equipment room be located?
- A Within the IT equipment room itself, next to the served equipment
- B Inside a locked electrical room accessible only to facility engineers
- C At an approved location readily accessible to authorized personnel and emergency responders in case of fire
- D Adjacent to the building's main service disconnect only
Show answer & explanation
Correct: C — At an approved location readily accessible to authorized personnel and emergency responders in case of fire
645.10(A)(1) requires the controls to be at an approved location readily accessible to authorized personnel and emergency responders in a fire. A locked room limited to engineers, a spot tied only to the main service disconnect, or placement inside the served room itself don't guarantee that fast, responder-accessible access.
Conditions unlocking alternative wiring methods
NEC 645.4 An IT equipment room only gets to skip Chapter 3, Article 725, and Article 770 wiring methods if it meets all six conditions in 645.4 at once.
Q2 NEC 645.4
An information technology equipment room meets five of the six conditions in 645.4, but its walls and ceiling are not fire-resistant-rated. What is the result?
- A The alternative wiring methods do not apply, and Chapter 3, Article 725, and Article 770 requirements govern the room
- B Only the fire-resistant-rating condition is waived, and the rest of the alternative methods still apply
- C The room can use alternative wiring methods only for signaling and optical fiber cabling, not power wiring
- D The alternative wiring methods still apply because a majority of conditions are met
Show answer & explanation
Correct: A — The alternative wiring methods do not apply, and Chapter 3, Article 725, and Article 770 requirements govern the room
Section 645.4 requires that all listed conditions be met before the alternative wiring methods to Chapter 3 and parts of Articles 725 and 770 are permitted. There's no partial-credit or majority-rules provision — missing the fire-resistant-rated separation condition in 645.4(5) means the exception doesn't apply at all, and standard wiring methods govern the whole room.
Branch-circuit sizing and power-supply cords
NEC 645.5(A) IT equipment branch circuits need 125% of the connected load in ampacity, and power-supply cords are capped at 15 ft with listed components throughout.
Q3 NEC 645.5(A)
A data center room has IT equipment with a total connected load of 40 A. What is the minimum required ampacity of the branch-circuit conductors under 645.5(A)?
- A 40 A
- B 50 A
- C 44 A
- D 60 A
Show answer & explanation
Correct: B — 50 A
645.5(A) requires branch-circuit conductor ampacity of not less than 125% of the total connected load. For a 40 A connected load, that's 40 × 1.25 = 50 A. Sizing at just the connected load (40 A) ignores the required margin, and 44 A reflects a mistaken 110% factor rather than 125%.
Communications wiring and cable routing in IT rooms
NEC 645.3(F) Comms wires, cables, raceways, and equipment in an IT equipment room must be listed under Article 800, and Article 645 governs how that equipment gets its power.
Q4 NEC 645.3(F) Code lookup
A data center technician is running new Cat6 communications cables inside an information technology equipment room. Which section specifies that the cables must be listed in accordance with 800.179 and that only listed cable routing assemblies, raceways, and equipment are permitted in that room?
- A 645.5(C)
- B 645.3(B)
- C 645.3(F)
- D 645.3(I)
Show answer & explanation
Correct: C — 645.3(F)
645.3(F) is the section that requires communications wires, cables, cable routing assemblies, and equipment installed in an IT equipment room to be listed per 800.179, 800.182, and 800.171, and applies Parts I-V of Articles 800 and 805. 645.3(I) instead governs cables that are NOT located in the IT equipment room, so it doesn't fit a scenario about cables being run inside the room.
Exception: skipping remote disconnect for critical ops data systems
NEC 645.10(B) A critical operations data system can skip the 645.10(A) remote disconnect only if five conditions are all met at once — a written power-down procedure, on-site qualified personnel, smoke detection, fire suppression, and compliant under-floor cabling.
Q5 NEC 645.10(B)
A critical operations data system room omits remote disconnecting controls. Which of the following, by itself, is enough to justify this under 645.10(B)?
- A An approved fire suppression system is installed, with detection to be added later
- B A smoke-sensing fire detection system is installed
- C Qualified personnel are available during business hours only
- D All five conditions in 645.10(B), including procedure, personnel, detection, suppression, and cabling compliance, are met together
Show answer & explanation
Correct: D — All five conditions in 645.10(B), including procedure, personnel, detection, suppression, and cabling compliance, are met together
645.10(B) requires all five listed conditions to be met simultaneously before remote disconnecting controls can be omitted. Having only fire detection, or only suppression, or personnel available part-time does not satisfy the exception — qualified personnel must be continuously available per 645.10(B)(2), not just during business hours.
Equipment grounding and bonding of IT system parts
NEC 645.15 Every exposed metal part of an IT system must bond to the equipment grounding conductor per Article 250 unless the equipment is double insulated.
Q6 NEC 645.15
Under 645.15, exposed non-current-carrying metal parts of an information technology system must be bonded to the equipment grounding conductor in accordance with Article 250, EXCEPT where the equipment is:
- A Double insulated
- B Connected to an auxiliary grounding electrode
- C Served by an isolated grounding-type receptacle
- D Located on a raised access floor
Show answer & explanation
Correct: A — Double insulated
645.15 allows double-insulated equipment as the sole exception to the bonding requirement. An isolated grounding-type receptacle (referenced via 250.146(D)) still requires the equipment grounding conductor connection, and an auxiliary grounding electrode under 250.54 is a supplement, not a substitute, for that bond.
Fire-resistant boundary penetrations and plenum wiring
NEC 645.3(A) Anything that pierces the IT room's fire-resistant boundary or runs in the plenum above it must meet the applicable Chapter 3 and Chapter 7/8 wiring rules, not just Article 645.
Q7 NEC 645.3(A)
A cable tray penetrates the fire-resistant wall of an information technology equipment room. Which section applies to sealing that penetration?
- A 300.21
- B 645.4
- C 300.22(C)(1)
- D 645.10
Show answer & explanation
Correct: A — 300.21
645.3(A) points to 300.21 (plus 770.26 and 800.26 for communications/fiber) for spread of fire or products of combustion through the fire-resistant room boundary. 300.22(C)(1) applies to wiring within plenums, not boundary penetrations, so it's the wrong reference for this scenario.
Cords, data cables, and fiber permitted under raised floors
NEC 645.5(E)(2) Whether the space under a raised floor allows plenum-rated cable or requires it depends on one thing: is there an automatic fire suppression system?
Q8 NEC 645.5(E)(2)
An information technology equipment room has a raised floor with no automatic fire suppression system installed underneath. Which data cable type may be installed in that space?
- A Type CMG general-purpose cable
- B Type CL2 limited-use cable
- C Type CMP plenum cable installed per 722.135(E)
- D Type CMR riser cable
Show answer & explanation
Correct: C — Type CMP plenum cable installed per 722.135(E)
Per 645.5(E)(2)(5), without automatic fire suppression, only substitute cable Type CMP installed in accordance with 722.135(E) is permitted under the raised floor. CMR, CMG, and CL2 are only added to the permitted list when fire suppression is present, per 645.5(E)(2)(4).
CATV and radio distribution cabling in IT rooms
NEC 645.3(G) CATV and radio distribution cable and equipment in an IT equipment room must follow Articles 800 and 820, but Article 645 still governs how that equipment is powered.
Q9 NEC 645.3(G)
A contractor is installing community antenna television (CATV) distribution cable in an information technology equipment room. Which set of rules applies to the cable and equipment itself?
- A Parts I through V of Articles 800 and 820
- B Only the equipment grounding provisions of Article 250
- C Article 725 class 2 and class 3 circuit rules
- D Article 645 in its entirety, including cable listing requirements
Show answer & explanation
Correct: A — Parts I through V of Articles 800 and 820
645.3(G) states that Parts I, II, III, IV, and V of Articles 800 and 820 apply to CATV and radio distribution cables and equipment installed in an information technology equipment room. Article 645 in its entirety does not govern the cable — it only governs powering the equipment, not the cable/equipment listing itself. Article 250 and Article 725 are not the applicable references here.
Tagging cables identified for future use
NEC 645.5(H)(1) Supply and interconnecting cables held for future use in an IT equipment room need a durable tag showing when they were tagged, when they'll be used, and what for.
Q10 NEC 645.5(H)(1)
A supply circuit in an information technology equipment room is left in place for future use. Per 645.5(H)(1), what is required of the identifying tag?
- A It must be a metal tag permanently affixed with rivets
- B It must be replaced annually regardless of condition
- C It must be color-coded to match the circuit voltage class
- D It must be sufficiently durable to withstand the environment involved
Show answer & explanation
Correct: D — It must be sufficiently durable to withstand the environment involved
645.5(H)(1) sets a performance requirement — durability suited to the environment involved — not a specific material, color code, or replacement schedule. Metal-rivet tags, voltage color-coding, and annual replacement are not requirements of this section.
Optical fiber cable listing and bonding in IT rooms
NEC 645.3(H) Optical fiber cable in an IT equipment room must be listed per 770.179, and any conductive members must be bonded and grounded per 770.114.
Q11 NEC 645.3(H) Code lookup
An electrician is installing new optical fiber cable in an information technology equipment room. Before pulling the cable, which section specifies the listing requirement the cable itself must meet to be permitted in that room?
- A 645.3(I)
- B 645.5(D)
- C 645.3(H)
- D 645.3(F)
Show answer & explanation
Correct: C — 645.3(H)
645.3(H) is the section that requires optical fiber cable in an IT equipment room to be listed per 770.179. 645.3(F) covers cable routing assemblies and communications wiring generally, 645.3(I) addresses cables that leave the IT room rather than the listing standard for cables inside it, and 645.5(D) is physical protection for supply/interconnecting cables, not fiber listing.
Physical protection for supply cords and cables
NEC 645.5(D) In an IT equipment room, any power-supply cord, branch-circuit conductor, or interconnecting cable must be protected wherever it's exposed to physical damage.
Q12 NEC 645.5(D)
In an information technology equipment (ITE) room governed by Article 645, what triggers the physical protection requirement in 645.5(D) for a branch-circuit supply conductor?
- A The conductor is longer than 6 ft (1.8 m)
- B The conductor is routed under a raised floor
- C The conductor supplies more than one piece of IT equipment
- D The conductor is exposed to physical damage
Show answer & explanation
Correct: D — The conductor is exposed to physical damage
645.5(D) is triggered by exposure to physical damage, not by routing location, length, or how many loads the conductor serves. Raised-floor routing is common in ITE rooms, but that alone doesn't create the duty — only damage exposure does.