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National Electrical Code Articles and Information

Based on the 2011 NEC

by Mark Lamendola

National Electrical Code Top Ten Tips: Article 645, IT Equipment

Why do we have Article 645? Did the IT (Information Technology) people decide they felt left out, so they had an article created to make them feel important? No, that's not it. Article 645 exists because an IT room (which is any room that conforms to NFPA 75) contains hazards not found in non-IT rooms.

  1. For one thing, an IT room doesn't lose all power just because first responders shut off the main. The computer equipment is on a UPS, or may even be on an alternate source such as an emergency generator.
  2. For another, the raised floors common in IT rooms add a layer or two of difficulty to reducing the spread of flame and smoke.

And those are only two contributors to the difficulty that IT rooms present to fire containment and fire response.

Another issue that often inserts itself into the discussion of IT room requirements is whether the equipment inside it is really IT equipment or if it's communication equipment. That is, does the equipment fall under Article 645 or under Article 800? The short answer is no matter what equipment is in a room, if that room conforms to NFPA 75 it's an IT room. You may have operational, engineering, and reliability issues to sort out if you're jamming different systems into the same room.

  1. This article covers the IT equipment and related wiring in an IT room. Basically, if it's an IT room, this article covers everything in it.
     
  2. An IT room is any room that meets the definition presented in NFPA 75:3.3.9; that is, it's any room that contains IT equipment [645.2].
     
  3. Any communications penetrations to that room must comply with 800.26 and/or 820.26 (where applicable) 645.3].
     
  4. Bond all metallic objects [645.15], for reasons that are detailed in IEEE-142, and to meet the requirements of Article 250, Part V. This eliminates differences of potential. And, yes, the non-current carrying metallic parts of fiber optic cables must also be bonded [645.3(C)].
     
  5. Article 645 allows you to use wiring methods that are an alternate choice to those in Chapters 1 - 4, provided you meet the requirements of Section 645.4.
     
  6. IT loads are high-harmonic loads. Thus, you don't need to decide whether a load is continuous or noncontinuous in deciding whether to apply the 125% rule to IT branch circuits. It applies, regardless of whether the loads are continuous or noncontinuous.
     
  7. Only certain cable types are permitted under raised floors. See Table 645-5 for what these cable types are.
     
  8. The iconic feature of an IT room is the remote disconnect[645.10] typically mounted near the door of the room. Usually, there's also a sign that sternly warns against operating it unless there's an emergency. As with any disconnect, this should be mounted such that the operator stands to the right of the switch and pulls down with the left hand to open it. Remember, this switch is operating under load. You don't want to place a person in the blast path. The enclosure will mute the blast somewhat, but will not provide complete protection.
     
  9. The remote disconnect must also disconnect the HVAC [645.10(A), and disconnect the UPS from its loads [645.11].
     
  10. For critical operations data systems, remote disconnecting controls aren't required if the installation meets all the requirements of 645.10(B).

 

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How the NEC is arranged

  1. The first four Chapters of the NEC apply to all installations.
  2. Article 90 precedes Chapter One, and establishes the authority of the NEC.
  3. Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
  4. Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
  5. Chapter 8 provides the requirements for communications systems.
  6. Chapter 9 provides tables.
  7. The appendices provide mostly reference information.
  8. Appendix D contains examples that every NEC user should study.

Try your NEC moxy:

  • Do you know the difference between bonding and grounding? Hint: Look in the NEC, Article 100.
  • Does the NEC refer to grounding incorrectly in any of its articles? Yes! So be careful to apply the Article 100 definitions. Don't ground where you should bond.
  • When doing motor load calculations, which Article covers hermetic motors? Answer: While Article 440 covers the application of hermetic motors, it does so only by amending Article 430 because hermetic motors are a special case of motors. For motor load calculations, refer to Article 430.
  • Does the NEC provide a voltage drop requirement? Yes! It does so in a special case, which is Article 648 Sensitive Electronic Equipment. But for general applications, it does not provide a requirement; it merely provides a recommendation in a couple of FPNs.
  • Take our Code Quizzes.

Remember other applicable codes, rules, standards, and references:

  • OSHA's electrical worker safety rules.
  • IEEE standards.
  • NETA standards.
  • NFPA standards.
  • International Codes (if applicable to the installation).
  • State Codes (if the state has them).
  • Local ordinances and permit requirements.
  • Local fire codes.
  • Manufacturer requirements or guidelines.
  • Customer security requirements.
  • Industry standards.
  • Your company's own internal standards, practices, and procedures.
  • Engineering drawing notes.

 

 

 

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