A major consideration in the design of a data center is whether the Information Technology Equipment (ITE) space
will comply with Article 645 of the National Electrical Code (NEC). Article 645 covers equipment, power supply wiring, equipment interconnecting wiring, and grounding of information technology equipment and systems. Chapters 1 through 4 of the NEC establish the mandatory minimum requirements for electrical installations in typical facilities. If we comply with Article 645, we can ignore some of the most burdensome of the mandatory requirements in Chapters 1 through 4.
To assist you, we have identified the major differences in design, planning and operation between data centers that comply with Article 645 and those that do not comply. In this comparison we have utilized the 2008 version of the National Electrical Code that is enforced by most local authorities with jurisdiction.
Non-Article 645-compliant space headaches
A non-Article 645-compliant space must meet the requirements of Chapters 1 through 4. These requirements are most relevant and burdensome in an ITE space with a raised floor used as an air plenum, and limit the electrical system flexibility and maintainability desired in ITE spaces.
- Cabling installed below the raised floor that is used as an HVAC air path must be plenum rated.
- Electrical raceways are limited to those that do not have a combustible outer covering and flexible metal conduit is limited to lengths of 4 feet.
- All raceways and devices must be securely fastened.
- Corded equipment receptacle connections must be made above the raised floor.
- NEC 300.22 requirements for wiring in ducts, plenums and other air-handling spaces apply.
Article 645-compliant ITE space reduces requirements
These are the pluses that increase the electrical system flexibility and maintainability desired in ITE spaces. Note that these pluses do not include increased availability (uptime) of the computer equipment.
- Relaxed restrictions on cabling installed below the raised floor that is used as an HVAC air path.
- Electrical raceway restrictions are reduced.
- Cable tray may be used beneath the raised floor.
- Raceways and devices are not required to be securely fastened.
- Corded equipment receptacle connections may be made below the raised floor.
Article 645 sounds good. What's the catch?
Like most things in life, Article 645 is not a free lunch. The writers of Article 645 are saying, "OK, we will let you ignore some of the most burdensome requirements of Chapters 1 through 4, but you will have to pay a price." The price is requirements that increase fire safety and speed of shutdown in an emergency. These are the minuses that you must consider when evaluating the pluses.
- Compliance with NFPA 75-2003, "Standard for the Protection of Information Technology Equipment."
- An approved, manually initiated means to disconnect power to all electronic equipment in the space or in zones within the space. A similar means to disconnect the power to all dedicated HVAC systems serving the space or zones within the space -- this means must also close all required fire/smoke dampers. The control for these means shall be grouped, identified and readily accessible at principal exit doors. Both disconnecting means may be combined into one means. This requirement is commonly known as the "EPO" system.
- A separate HVAC system that is dedicated for the ITE space use and separated from other areas of occupancy. If the HVAC system serving the ITE space also serves areas outside the ITE room, fire/smoke dampers are required at the point of penetration of the space boundary. These dampers must close on activation of smoke detectors located below the raised floor and also on operation of the HVAC portion of the EPO system.
- All under-floor air circulation must automatically cease if fire or products of combustion are detected under the raised floor.
- The ITE space shall contain only listed technology equipment.
- The ITE space can only be occupied by personnel needed to maintain and operate the installed ITE equipment.
- The ITE space must be separated from other occupancies by fire-resistant-rated walls, floors, and ceilings with openings.
- Finally, having the EPO system and HVAC shutdowns will not increase the availability (uptime) of the computer equipment. These features increase the risk of an unintended computer outage due to human error.
In summary, complying with Article 645 allows for:
- Relaxed wiring means and methods below the raised floor.
- Equipment receptacles to be located below the raised floor.
- Use of cable tray below the raised floor.
This makes for easier installation and modifications to the IT equipment that changes often. It is not unusual for many ITE room operators to refresh their computer hardware every three years, so the equipment comes and goes daily. However, the availability (uptime) of the electrical and mechanical systems is lessened because of the requirements for an EPO system and automatic shutdown of HVAC systems upon detecting smoke under the raised floor. The decision gets back to a value judgment that you and your client need to make together.
ABOUT THE AUTHORS:
Kevin Meyer is the project manager and principal of the Florida region for Syska Hennessy Group. He has over 10 years experience as an electrical consulting engineer of highly complex facilities. Kevin focuses on design efforts to achieve energy efficiency, reliability and flexibility, with an emphasis in emergency/redundant power critical to the function of a data center environment.
Christopher Johnston is a Vice President and Chief Engineer for Syska's National Critical Facilities Team, the head of Syska's Critical Facilities' Technical Leadership Council and a member of Syska's Green Critical Facilities Committee. He leads research and development efforts to address technical issues in critical and hypercritical facilities, and specializes in the planning, design, construction, testing and commissioning of critical 24/7 facilities. Johnston brings 38 years of engineering experience in the field. Johnston is also regular presenter at conferences such as Data Center Dynamics and the Uptime Institute.
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