Nov 2008

Protecting Electrical Rooms Containing Grouped Power Cables.

During inspections of electrical rooms, property loss prevention engineers should determine how much of a presence there is of “grouped power cables.” There are no clear definitions or criteria as to what amount of cables (i.e., amount of cables per volume) are sufficient to necessitate fire protection.

According to NFPA Fire Protection Handbook 19th Edition, about 10% of industrial or manufacturing facility fires are caused by electrical distribution systems such as lighting, switchgears, wiring, over-current protection devices etc. High voltage electrical equipment items can cause fire especially when they are poorly maintained. The fire can spread on the combustible jacketing of power cables, particularly where grouped cables exist. In many cases, they are the only concentration of combustibles (see Note 1) in the rooms. A fire originating in an electrical room is, however, unlikely to spread outside the room since most electrical rooms are normally constructed of one or two hour fire rated walls (or partitions). The amount of combustibles (other than power cables) has already been limited to the absolute minimum, assuming there are no oil insulated transformers or fuel oil tanks for emergency generators (see Note 2).

The greatest concern for such power cable fires is business interruption. Assuming a fire occurs in the main switch room where the high voltage power feeders directly come from the local power supplier, power can be interrupted for the entire facility, and full recovery might not take place within a week. A fire in a small electrical room can also affect the facility operations if the cables supply power to vital equipment, especially those related to production.

Once the amount or concentration of cables is determined to be unacceptably high (i.e., presence of grouped cables), there are four options according to FM Global Property Loss Prevention Data Sheets 5-31, “Cables and Bus Bars:”

1) Automatic sprinklers
For facilities where automatic sprinklers are already installed in the areas near the electrical rooms in question, it is relatively easy to extend sprinkler protection to the electrical rooms at minimal cost. However, local authorities, electrical engineers/inspectors, or facility managers may be reluctant to install wet type automatic sprinklers in electrical rooms, due to concerns of unwanted water discharge or leakage where there is no actual fire.

According to NEC 110.26 (also known as NFPA 70), automatic sprinkler installation is allowed in electrical rooms where equipment is 600V or less, except for certain spaces called “Dedicated Electrical Space.” These spaces are directly above the electrical equipment (please refer to NEC 110.26 for exact definition). All other spaces in electrical rooms can be protected by wet type automatic sprinklers. According to NFPA, unwanted water leakage events from sprinklers are very rare, occurring with only one in 16,000,000 sprinkler heads.

There are frequent automatic sprinkler installations in electrical rooms in the United States.

2) Coating Cables
When grouped cables exist in small areas of large electrical rooms, it may be practical and cost effective to provide an approved fire protection coating on the power cables. However, it may be impossible or difficult to work on existing live high voltage cables if the facility needs to operate continuously.

3) Clean Agent Suppression System
Gaseous suppression systems are frequently seen in electrical rooms in Asia. Clean agents such as nitrogen, Inergen, FM200 or other inert gases are more commonly used, and they are much safer than carbon dioxide. In many cases, gaseous suppression systems would be the most expensive choice among these options – especially when the protected room volumes are large or when there are multiple electrical rooms scattered within the facility.

4) Carbon Dioxide Suppression System
Carbon dioxide systems should be avoided, since carbon dioxide is highly toxic. Carbon dioxide should be used in an enclosed machine so it does not affect life safety.

If none of these four options can be implemented due to the cost or other reasons, power cables should be separated as much as possible by re-routing, so that “groups” are not created (again, there are no clear rules as to how far they should be separated). Smoke detectors should be installed at the ceiling level and inside cabinets or sub-floors where practical, and infrared inspections should be conducted for all equipment items at least once a year.

Note 1: Fire protection is not needed if the cable is FM Global Group 1, UL 910 plenum rated or flame spread does not exceed 1.5 m (5 ft) when tested in accordance with NFPA 262.

Note 2: Protecting indoor oil insulated transformers or emergency generators are not within the scope of this article.

Risk Logic can help provide options for protection within your electrical rooms.