Last month, I provided a basic outline and history of Critical Operations Power Systems (COPS) located in Article 708 of the National Electrical Code. This article features details about Article 708 and the differences between a normal installation and COPS system.
The first and most important step is to conduct a risk assessment at the location to identify any naturally occurring hazards such as earthquakes and tsunamis; hurricanes, tornadoes and nor’easters; and airborne chemicals from chemical plants, railway derailments with chemical spills and nuclear emergencies.
Risk hazard assessments must also take into consideration the possibility of human-caused accidents, intentional events and range and forest fires that can cause major damage and devastations. Once the risk assessment has been done and the potential hazards identified, a strategy must be developed and implemented to mitigate the specific hazards based on prescriptive requirements in Article 708.
The requirements in Article 708 address more than any of the requirements in Article 700 for emergency systems with the mission-critical facilities having to operate for a much longer time than normal emergency applications. Physical security must be provided for the electrical COPS, with electrical circuits and equipment only being accessible to qualified personnel.
In a building or at a structure where a COPS and any other type of power system are present, all boxes and enclosures (including transfer switches, generators and power panels) for COPS circuits must be permanently marked so they will be readily identified as a component of the COPS. In a building in which COPS are present with other types of power systems described in other sections in this article, the cover plates for the receptacles or the receptacles themselves supplied from the COPS must have a distinctive color or marking to be readily identifiable. Nonlocking-type, 125V, 15A and 20A receptacles supplied from the COPS shall have an illuminated face or an indicator light to show there is power to the receptacle. These requirements are not expensive to accomplish during initial construction.
Wiring of two or more COPS circuits supplied from the same source are permitted in the same raceway, cable, box or cabinet. However, wiring from a COPS source or COPS source distribution overcurrent protection to critical loads must be kept entirely independent of all other wiring and equipment.
This requirement is similar to the requirements in Article 700 for emergency equipment and in Article 517 for critical circuits in hospitals that ensure normal circuit failures will not adversely affect emergency circuits or critical circuits. COPS feeders must be protected from physical damage by installing the feeders in rigid metal conduit, intermediate metal conduit or Type MI cable. Schedule 40 PVC or Schedule 80 PVC, RTRC, EMT, flexible nonmetallic or jacketed metallic raceways or jacketed metallic cable assemblies listed for installation in concrete can be used for physical protection, but only where encased in not less than two (2) inches of concrete. This would be very difficult and expensive to retrofit into an existing building.
The feeders mentioned above must meet one of the following requirements: (1) The cable or raceway is protected by a listed electrical circuit protective system with a minimum 2-hour fire rating. (2) The cable or raceway is a listed fire-resistive cable system with a minimum 2-hour fire rating. (3) The cable or raceway is protected by a listed fire-rated assembly that has a minimum fire rating of 2 hours. (4) The cable or raceway is encased in a minimum of 50 mm (2 in.) of concrete.
A wall and an electrical circuit
The 2-hour rating of a wall is much different than the 2-hour rating of an electrical circuit. At the end of a 2-hour fire test on an electrical conduit with wires, its insulation must be intact, and the circuit must function electrically: no short circuits, grounds or opens are permitted. A wall subjected to a 2-hour fire resistance test must only prevent a fire from passing through or past the wall, without regard to wall damage. For HVAC wiring, fire alarm, security, emergency, communications and signaling systems, rigid metal conduit, intermediate metal conduit or Type MI cable must be used.
There are many additional requirements in Article 708 that I have not covered but are necessary to ensure critical mission facilities are going to operate during and after major disasters. Contact me if you have any questions.