Last month, I covered common power quality phenomena with regards to the National Electrical Code (NEC). Two articles address specific topics related to power quality: Article 647, Sensitive Electronic Equipment, and Article 708, Critical Operations Power Systems (COPS). There also is Article 645, Information Technology Equipment, which seems a bit out of place because information technology (IT) equipment is generally among the top equipment on most people’s lists for what is called “sensitive electronic equipment.” Still, the NEC treats it separately.

Article 645, Information Technology Equipment, “covers equipment, power-supply wiring, equipment interconnecting wiring, and grounding of information technology equipment and systems, including terminal units, in an information technology equipment room.” However, the references to situations that might involve power quality are indirect at best, such as Article 645.4(6), under “Special Requirements for Information Technology Equipment Room,” which limits putting other equipment that is not related to the operation of the room. This helps keep other equipment from causing power quality problems to the IT equipment. It also helps keep conductors from causing too large a voltage drop for the loads in 645.5 and grounding in 645.15, but it’s not overly useful from a power quality perspective.

This article also contains the somewhat controversial 645.10, which requires a shutoff switch to be readily accessible from the exit doors, creating a deliberate interruption to the process when not used during fire or other emergency situations. On an unrelated power quality note, it contains probably one of the most violated sections of the Code with respect to many facilities in Article 645.5(F): “Abandoned Supply Circuits and Interconnecting Cables. Abandoned supply circuits and interconnecting cables shall be removed unless contained in a metal raceway.” If nothing else, that would make troubleshooting a bit easier.

Article 647, Sensitive Electronic Equipment, covers some of the same topics in the IEEE Std. 1100, Recommended Practice for Powering and Grounding Electronic Equipment, also known as the Emerald Book. The big difference is that one is the law (in most states), and the other is a recommended practice. Article 647 specifically “covers the installation and wiring of separately derived systems operating at 120 volts line-to-line and 60 volts to ground for sensitive electronic equipment.” Now, some data centers can operate with other voltage levels, and there’s the latest push toward DC voltage distribution within data centers. One could look at Article 647 as providing “some direction for designers and installers to resolve power quality issues without creating a dangerous situation.” More specifically, it has tight tolerances on permissible voltage drops in 647.4(D) and grounding in 647.6, including marking the equipment-grounding conductor and the infamous orange colored isolated-ground receptacles in 647.7(B) to help minimize putting potential disruptive or “polluting” loads on same circuits.

Article 708, Critical Operations Power Systems (COPS), was new in the 2008 revision of the NEC. COPS are defined as “power systems for facilities or parts of facilities that require continuous operation for the reasons of public safety, emergency management, national security, or business continuity.” Following some of the large-scale disasters in the United States, such as the terrorist attacks of Sept. 11, 2001, and Hurricane Katrina, the need for “hardening” such facilities (or parts of the facilities known as the designated critical operations areas) for longer sustained operations was the basis behind the new CMP. The original draft contained a fine print note (FPN) that indicated the types of facilities to fall under the COPS category: air traffic control centers; fire and security system monitoring; hazardous material handling facilities; communication centers and telephone exchanges; financial, banking, and business data processing facilities; fuel supply pumping stations; hospitals; water and sewage treatment facilities; 911 centers; and critical government facilities, including police, fire and civil defense facilities. These are the same types of facilities that are often the sites of power quality investigations, permanent power quality monitors, and/or where mitigation equipment is installed.

Article 708’s scope is in line with power quality concerns, as it applies “to the electrical installation, operation, monitoring, control, and maintenance of critical operations power systems consisting of circuits and equipment intended to supply, distribute and control electricity to designated vital operations in the event of disruption to elements of the normal system.”

Some of the concepts Article 708 introduces directly impact power quality issues. These concepts include commissioning, performing periodic maintenance and testing all critical power systems during maximum anticipated load conditions, and physical security. Keeping the operation running properly requires a baseline of data from the commissioning along with ongoing tests, proactive maintenance programs to help eliminate problems before they occur (such as tightening connections), and ensuring unauthorized personnel cannot disrupt the operation. Documentation of the test results is a key part of the article, which helps solve power quality problems. These are all good concepts for all facilities concerned with keeping the operation running smoothly from potential power quality problems.


BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680.