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Disconnecting Means Requirements as Stated in 645-10 and 11

Posted By Robert Jones, Monday, January 01, 2001
Updated: Tuesday, February 12, 2013

For several years I have heard horror stories associated with the accidental activation of the disconnecting means required by Sections 645-2(a), 645-10, and 645-11. Roger Witt, representing State Farm Insurance Company, submitted several Code change proposals to delete the requirement in the 2002 NEC. Mr. Witt’s substantiation is as follows:

The disconnecting means requirement presents a problem with accidental or malicious activation and in some cases presents problems to equipment and processes external to the data room. Accidental or malicious shutdown of a data center causes a large economic hardship on businesses that rely heavily on data processing centers. The two issues addressed by the "disconnecting means” the shutdown of the electrical source and air supply to the room are addressed in other parts of the NEC and other NFPA standards. Identification of power source locations is covered in the NEC Sections 230-2(e) and 700-8. With this knowledge, the power source can be located and disconnected. With smoke detectors installed on the ceiling of the data room, under the raised floor, and in air handling systems of 2000 cfm or more (NFPA 90-A, chapter 4), the shut down of the air handling system is addressed. Also, requirements for using cable types meeting flame test under the raised floor by either the NFPA or model building codes help in reducing the propagation of fire and smoke. In some data rooms automatic fire sprinklers are required, adding yet another means to help reduce the destructive affects of a fire. With the power source locations identified and the installation of smoke detectors, fan shutdown systems upon the sensing of smoke, fire sprinklers, and flame spread rated cables, it seems that protection is provided without the need for a single switch that will turn off the power to the entire data room.

This proposal was rejected by CMP-12 because it lacked sufficient technical merit and documentation of problems associated with this requirement. As stated above, I have heard stories of accidental activation of the disconnecting means, but how many times has it actually happened and what was the cost impact of each occurrence? Is there really a problem with this requirement or is the requirement being misinterpreted?

Before the code panel meeting, I asked for input from the members of NFPA 75. Ten members responded and they were overwhelmingly opposed to the deletion of the disconnecting means for the following reasons:

1. NFPA 2001 requires air ventilation systems to shutdown prior to discharge of gaseous agents because their continued operation would adversely affect the performance of the fire extinguishments agent system.

2. Most of the fires start due to short circuitry. Power shut down requirements to the equipment helps to cut fuel supply.

3. Code requires means to shut down power manually when other means to shutdown power to the fans or equipment does not happen.

4. The single disconnect switch provides a means of shutting off all electric power to the computer room. The assumption is that the electric power is a source of ignition, which must be eliminated to permit successful fire extinguishments.

5. The need to find multiple power disconnects during a fire is theoretically eliminated.

6. The requirement for a power disconnect has always been included in the standard.

7. The potential for an electrical fire in the computer room is high due to the quantity of equipment and wiring and the large power demand.

8. Limit the damage and spread of fire among the electronic equipment.

9. The means to disconnect power to all electronic equipment with a marked main power shutoff switch allows for a quick restriction of the fire energy source and limiting the fire and, thus, reducing the overall damages.

10. Water can be cleaned from EDP equipment with little damage as long as the equipment was not energized when it was wet down.

11. An increased potential for injury or death, as computer site personnel will no doubt need to visit every panel in the room to disconnect power, absent the existence of a centralized EPO switch (push button or panic button).

12. Electrical fire is a very likely scenario in a computer room.

13. Being able to quickly shut down power could also expedite manual fire fighting using water.

14. No one can expect the computer room operator to go to the service disconnect in some electrical equipment and switchboard room and trip the breaker.

15. All clean agent extinguishing systems, in a computer room, have been designed under de-energized conditions.

16. A computer room operator will become aware of a problem in advance of the automatic detection and suppression systems and any necessary shutdowns can be done in advance of the automatic functions.

Why is this disconnecting means a requirement of the NEC? Section 90-1 states that "the purpose of the Code is the practical safeguarding of persons and property from the hazards of the use of electricity.” An argument could be made that the information technology equipment is being protected, but is it actually being protected from the use of electricity?

Another argument could be made that the intention of this requirement is to protect fire fighters by disconnecting all power in this area. This is an interesting argument because if this is the intention, then all UPS systems should be required to shut down in the event of a fire and not just a UPS system associated with information technology equipment installed in accordance with Article 645 of the NEC.

The computer people seem to want to minimize the damage to their equipment in the event of a fire. The stated purpose of NFPA 75 is "to set forth the minimum requirements for the protection of electronic computer/data processing equipment and computer areas from damage by fire or its associated effects—namely, smoke, corrosion, heat, and water.” The disconnecting means definitely serves this purpose.

Is a countdown system with regard to a disconnecting means a violation of the NEC? Article 100 defines disconnecting means as "a device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of power.” By this definition it seems that a countdown type of disconnecting means would be acceptable. A countdown type of system makes sense because if the disconnecting means were activated by accident, the operator would have time to override it. Also, protective covers should be used to prevent accidental activation.

Article 685 has been cited as giving permission for an orderly shutdown of information technology equipment: however, the scope of Article 685 is very specific. In accordance with Article 685, an integrated electrical system is a unitized segment of an industrial wiring system where certain conditions are met. An information technology equipment room in a typical commercial building would have a hard time fitting this description.

Confusion may have been added to this disconnecting means because CMP-12 accepted a proposal that states, "Where a push button is used as a means to disconnect power, pushing the button in shall disconnect the power.” It needs to be stressed that if this proposal becomes a part of the 2002 NEC it does not require the disconnecting means to be a button. Article 645 does not specify what type of disconnecting means to use; it only states that a means to disconnect power to all electronic equipment shall be provided.

Code Panels make changes to the NEC by voting on proposals. These proposals must be properly submitted with sufficient technical information and documentation so that panel members can formulate an opinion.


Read more by Robert Jones

Tags:  Featured  January-February 2001 

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