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Top five NEC 708 guidelines

9/1/2009

Article 708, new to the 2008 National Electrical Code and the most stringent of the 700 Section Articles, provides an additional level of protection for electrical equipment and wiring so that in the event of a natural or human-created disaster, the facility will still function while other facilities may fail.

Article 708 has enhanced the local authority having jurisdiction's (AHJ) ability to ensure uniform enforcement for critical facilities. These facilities can consider either a designated area or the entire building as part of the critical operations power systems (COPS). This article requires that the alternate power source have a minimum of 72 hr of full-load capacity. It also requires transient voltage surge suppressor protection be included in all COPS equipment. Finally, it provides additional protection from fire and water damage for COPS equipment, power wiring, and communication cables by considering the 100-yr flood plain.

Here are five actions you should consider to help you comply with Article 708.

Codes 1
Figure 1: This shows the different types of emergency loads: COPS loads, emergency loads, legally required standby loads, and optional standby loads. Source: 2008 NEC, Tommy Bufford

1. Perform a risk assessment

COPS generally are installed in vital facilities that if destroyed or incapacitated would disrupt national security, the economy, public health, and/or safety. The local AHJ has the authority to subject a designated area, or all of the facility, to these new requirements. If a designated area in the facility is subject to this section of the code, it is referred to as the designated critical operations area (DCOA).

As a part of the additional requirements for this section of the NEC, a risk assessment shall be performed to identify the hazards and rank their likelihood of occurrence. At a minimum, the assessment should include naturally occurring hazards and human-caused events. Based on the risk assessment, a plan should be developed and implemented to mitigate the potential hazards. A facility with a COPS area also shall have a documented emergency operations plan.

2. Ensure full-load 72-hr continuous alternate power sources

According to NEC 708, the COPS alternate power source shall have the capacity and rating to run full load continuously for a minimum period of 72 hr. The alternate power source can be a generator, UPS, or a fuel cell system. It must have selective load pickup and load shedding capabilities as needed to ensure power to, in order of priority: “1) the COPS and emergency circuits, 2) the legally required standby circuits, and 3) the optional standby circuits.” (NEC 708.22(B))

If the DCOA is fed by a single generator source, a means for connecting a portable generator also should be provided. Fuel transfer pumps for prime mover type generators must be connected to the COPS branch distribution equipment. The on-site fuel supply shall be secured and protected according to the risk assessment plan.

3. Review all sources and circuits for grounding compliance

Remember that all sources of power shall be grounded as a separately derived source according to Article 250.30.

The COPS circuits must be supplied by dedicated automatic transfer switches (ATS). All other loads, including emergency loads not designated as COPS, must be supplied through additional ATS, so the loads are separated. When the primary service disconnecting means has ground fault protection, a second level of ground fault protection must be provided as well. This is similar to the Article 517 requirements. The ground fault protection shall be fully selective with a minimum of six cycles of separation between the service and feeder ground tripping bands.

4. Protect against physical damage

All feeder and branch circuit wiring for the COPS systems must be permanently marked so it can be easily identified. It also shall be kept entirely independent of all other wiring and equipment. Per the code, the circuit wiring must be protected by one of the following methods: “rigid metal conduit, intermediate metal conduit, or Type MI cable, EMT, or PVC Schedule 40 or 80, if encased in a minimum of 2 in. of concrete, reinforced thermosetting resin conduit (RTRC), flexible nonmetallic or jacketed metallic raceways, or jacketed metallic cable assemblies listed for installation in concrete.” (708.10(C)(1))

Feeder cables should meet one of the following conditions: “be a listed electrical protective system with a minimum of 1-hr fire rating, be protected by a minimum of 1-hr fire rated assembly, be embedded in minimum of 2 in. of concrete, or be a cable listed to maintain integrity for a minimum of 1 hr.” (708.10(C)(2))

5. Understand any special requirements such as 100-yr flood plain

There are special requirements when COPS feeders are installed in areas below the 100-yr flood plain, so be sure to review the code in detail.

This is a condensed summary of Article 708. When you are designing COPS, it is important to remember to refer to Article 708 in its entirety for specific code guidelines. For the complete source, refer to NFPA 70-2008 National Electrical Code Handbook.

Author Information
Bufford is a specification engineer with General Electric. His work encompasses a broad range of experiences as a design engineer, project manager, and specification engineer. Bufford holds a PE in North Carolina.
View the original article and related content on Consulting Specifying Engineer

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