Information Technology Equipment Rooms

Article 645 is optional — you only take on its rules if you want its benefits, like under-floor wiring and cable arrangements not allowed elsewhere. The price of admission is a room-wide emergency disconnect for both power and air handling.

Modern data centers push huge loads, and this single-button shutdown is a fundamental safety trade for the flexibility the article grants.

When it applies

This applies to purpose-built IT equipment rooms and data centers — not just a closet with a server, but a space meeting the article's conditions for construction and controlled access. The payoff is you can run cabling and power in the space under the raised floor, but the tradeoff is a required means to kill power and HVAC to the room in an emergency.

Common mistakes

• Claiming the article's flexibility without actually meeting the room construction and access conditions it requires.
• Wiring under the floor with methods that are not permitted there.
• Forgetting the disconnect must drop both the IT power and the dedicated cooling together.

In the field

When I commission a data room, I test the emergency disconnect for real and confirm it drops the CRAC units along with the racks. A room that keeps cooling running while the gear is supposed to be dead is not actually shut down.