Short answer: Article 645 is a set of special rules for information technology equipment (ITE) rooms, such as server and computer rooms. It is optional. It applies only when the room meets the conditions listed in the article, and then it allows some wiring methods that are not allowed elsewhere. In a room that uses Article 645, the ITE branch circuits are sized as a continuous load, which means 125% of the load (NEC 645.6(A)). Phone and data cabling follows its own limited-energy and communications articles, which the 2026 NEC reorganized.
PSI lists data and communications equipment in the Special Occupancies, Equipment and Conditions subject area of the Texas Journeyman exam: 6 scored NEC Knowledge questions and 3 scored Calculations questions. PSI does not say how many cover IT equipment alone. The Texas Journeyman Practice Pack has 1,000 original questions and 10 timed mock exams in the real two-part format, with step-by-step solutions for every calculation. Try free practice questions without signing up. Get the full pack for US$39 with one payment.
Tsai Electro is an independent learning site. Not affiliated with TDLR, PSI or NFPA. We explain the ideas in our own words and do not reproduce NEC text. Check every rule and table value in your own 2026 NEC, and follow your supervisor and the local inspector.
Article 645 is optional
Most offices with a few servers are wired under the general rules of Chapters 1 through 4. Article 645 is an option the designer can choose for a dedicated ITE room. To use it, the room must meet every condition the article lists. Those conditions cover things such as an emergency disconnecting means for the room’s equipment, a dedicated heating and air system or fire and smoke separation, listed equipment, access limited to the people who operate and maintain the equipment, and fire-resistive separation from other occupancies.
If all conditions are met, the room can use the article’s allowances, such as certain cables under a raised floor and interconnecting cables between pieces of equipment. If any condition is not met, the general code rules apply and Article 645 is not used.
On the exam, a common trap is to apply an Article 645 allowance to a room that does not meet the conditions.
Sizing ITE branch circuits
In an Article 645 room, the 2026 NEC treats ITE as a continuous load for its branch circuits (NEC 645.6(A)). Outside such a room, use the general branch circuit rules and treat any load expected to run 3 hours or more as continuous. Under the continuous load rule, the conductors and the overcurrent device are sized at 125% of the load. Earlier editions stated the 125% directly. The 2026 wording reaches the same number through the continuous load rule.
Worked example: a 208 V rack circuit
A rack of ITE draws 3,600 VA on a single-phase 208 V branch circuit.
- Load current: 3,600 ÷ 208 = 17.3 A.
- Continuous load: 17.3 × 1.25 = 21.6 A.
- Overcurrent device: the next standard rating at or above 21.6 A is 25 A (NEC 240.6(A)).
- Conductor: 12 AWG copper is limited to a 20 A overcurrent device by the small conductor rule (NEC 240.4(D)), so this example uses 10 AWG copper, assuming its ampacity still covers the load after any adjustment and correction.
- Check the terminal temperature ratings and any adjustment factors for the actual installation.
A 20 A circuit with 12 AWG would look close enough on the job, but it fails the 125% check.
Where communications wiring fits
Phone, data and similar communications cabling is not sized like power circuits. It follows its own articles for limited-energy and communications systems, and the 2026 NEC reorganized where those rules sit, so older study guides may point to the wrong article. On the job, look up the article for the type of cable you are installing in your own 2026 NEC, and follow the listing marked on the cable and the specification for the project.
Check yourself
- Does every room with servers have to follow Article 645? No. It is optional and applies only when the room meets all its conditions.
- A 2,400 VA ITE load is on a 120 V circuit. What current do you size for? 2,400 ÷ 120 = 20 A × 1.25 = 25 A.
- Why is 12 AWG copper not used on a 25 A breaker? The small conductor rule limits it to 20 A.
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Find Article 645 faster on exam day
NFPA 70, National Electrical Code, 2026 Edition (softcover). Highlight the list of conditions in 645 and the supply circuit rule, starting with whether the article applies at all. The Texas exam is open book. PSI allows a soft-bound NEC with highlighting, underlining and notes made in advance. Loose-leaf, spiral-bound and ring-bound copies are not allowed, and only permanent index tabs made or supplied by the NEC publisher are permitted; homemade and third-party tabs are not.
FAQ
Is Article 645 required for every server room?
No. Article 645 is optional. It applies only when the room meets every condition listed in the article.
Why are ITE branch circuits sized at 125%?
In an Article 645 room, the 2026 NEC treats ITE as a continuous load for branch circuits, and continuous loads are sized at 125% of the load.
Which part of the NEC covers communications cabling?
Communications cabling has its own limited-energy and communications articles, which the 2026 NEC reorganized. Check the index of your 2026 NEC for the cable type rather than relying on an older edition’s article numbers.
Is IT equipment on the Texas Journeyman exam?
PSI lists data and communications equipment in Special Occupancies, Equipment and Conditions: 6 scored NEC Knowledge questions and 3 scored Calculations questions.
Sources checked October 2026
- PSI Candidate Information Bulletin, Texas electrician examinations (updated September 15, 2026): https://test-takers.psiexams.com/api/content/bulletin/1682
- NFPA 70, National Electrical Code, 2026 Edition, Article 645, 240.4(D) and 240.6(A)
