Fire Pump - Overhead Conductors

[JTS]

I am working on a fire pump design for an industrial facility fed by overhead conductors. NFPA 20 considers a source to be reliable if it is not supplied by overhead conductors immediately outside the protected facility. As this is an industrial facility with various buildings and outdoor equipment is the 'protected facility' considered to be the entire complex, or is just the housing for the fire pump itself. Also, what exactly is 'immediately outside'?

 

[LCREP]

Can a fire in your building or next door impact the fire pump wire? If Yes not reliable, no you are good to go. Radiant heat must be considered for existing operations and or any future changes in exposures. Taking the fire pump out during a fire is not a good thing. Installing a diesel fire pump maybe another option.

 

[stookeyfpe]

A more thorough hazard analysis is required to answer this question. Frankly I would major concerns with using an overhead utility power line as a feed for a fire pump. Both NFPA 20 and NFPA 70 Article 695 pushes one to go underground - or - use protected cabling if the wiring is aboveground. In addition to LCREPs concerns I would be worried by other external exposures such as tornadoes, hurricanes or some unit process handing flammable or combustible liquids compromising the power supply to the pump.

 

[JTS]

Thank you for the responses. I think I need to clarify a bit. The vast majority of the sites I work at are in Oregon (paper and wood products mostly) and they are all fed from overhead lines by the utility. The biggest thing that we really have to worry about would be lightning strikes; however, this is mitigated using surge arrestors either on the poles themselves or the incoming side of distribution equipment. The way I understand it is that if I come in off the pole, onto a transformer, and then go underground to the pump house so fire equipment can get to the pump house without fear of overhead lines I should be ok. Is this correct, or do I need to move on and add a small generator to feed the fire pump as a backup?

 

[stookeyfpe]

Not being from Oregon, what happens when lightning strikes a branch circuit for a fire pump with a surge arrestor? I ask because doesn't a surge arrestor need to be sized for a given amperage and duration?

 

[JTS]

The surge arrestor is used for overvoltage protection, if a lightning strike happens the arrestor acts as a short to ground. I've always sized the surge arrestors based on the line voltage and the manufacturers table.