Figure 3: In this case, multiple fire pumps connected to three parallel generators/switchgear in a large complex facility are shown.
43
www.csemag.com Consulting-Specifying Engineer • MARCH 2015
414 full load amps, 2550 locked-rotor amps, 3-phase, and across-the-line start-ing. Conductor sizes are based upon 125% of full load current for the fire pump per NEC 695.6(B)(1) and (2) and for this application would be 414 fla x 1.25 = 517.5 amps (900 kcmil or parallel 300 kcmil, 75 C, XHHW per NEC Table 310.15(B)(16)).
A simple calculation of the transform-er size needed to stransform-erve this fire pump is (per NEC 695.5(A)) 125% of the full load amps or 1.25 x 414 fla x 460 V x 1.73/1,000 = 412 kVa. The next standard transformer size is 500 kVa. However, due to the inrush current, we’ll change our selection to a 1000 kVa transform-er. The transformer selected will be a 12,470 V delta to 277/480 V wye. This provides a neutral bonding connection on the secondary for any potentially needed control voltage power and is a common transformer size/configuration for ease of replacement should it ever fail. This
transformer is dedicated to the fire pump.
No secondary overcurrent or short circuit protection is allowed (NEC 695.5(B)).
Figure 1 represents a simple one-line con-figuration that complies with the intent of the code.
Now let’s consider the same building but with two fire pumps; the one dis-cussed above (350 hp) is located in the low-rise portion of the building while a second fire pump is located on the 15th floor of a 30-story tower. Let’s assume the second fire pump is a 100 hp, 460 V, 124 full load amps, 725 locked-rotor amps, 3-phase.
The transformer needed for this second fire pump would be calculated as done before, resulting in a load of 123 kVa, and we’ll select a 300 kVa transformer to serve this fire pump to ensure locked rotor currents can adequately be served within the voltage drop limitations. Fig-ure 2 represents one possible method of providing power for both pumps.
Let’s further complicate the needs by changing our building to a mega-resort with an estimated power demand of 26 MW served by three 10 MVa, 12.47 kV circuits each loaded to 9 MW or less.
Assume the owner of this facility has requested enough backup power to keep this facility running at a reduced capac-ity (i.e., not the entire central plant) for a short duration. The design engineer puts together Figure 3 with nine 2 MW paralleled generators, three to each of the three services. These are intended to parallel with each other and the utility. If one service is lost, enough generation is available to pick up the entire load con-nected by that one service. If two services are lost, approximately all of the loads would be served. If all three services are lost, approximately 2/3 of the facility load would be served. Because the loads are prioritized and priority 1 will serve NEC 700 loads plus fire pump load(s), we have been successful at serving the
Selecting fire pumps
Figure 4: A vertical fire pump and its associated controllers serve a high-rise complex.
44 Consulting-Specifying Engineer • MARCH 2015 www.csemag.com
fire pumps as a prioritized breaker from the paralleling system for normal power with emergency power coming from the emergency distribution system (priority 1 system).
Details to note
When sizing the transformers on the NEC 700 emergency system, care must be given by the engineer to allow for all loads plus the locked rotor current of the fire pump. Some drawbacks to increasing the size of the emergency system trans-former are the fault currents increase on the secondary side, which must be con-sidered for equipment ratings as well as arc flash considerations.
All three applications will require compliance for the normal power sup-ply conductors to be routed outside of the building or routed through the building in a 2 in. concrete envelope installed per NEC 230.6(1) and (2) as per NEC 695.6(A)(1). The standby gen-erator supply conductors are considered feeders and must meet the requirements of NEC 695.6(A)(2), which give three options. For the medium-voltage feeders there are two options per NEC 695.6(A)
(1) when routing through the building, either 2 in. concrete encasement or a 2-hour rated enclosure because 2-hour listed electrical circuit protective sys-tems are not available. The downstream feeders at standard voltages (i.e., 208 or 480 V) would be allowed to comply with all three options.
There are some medium-voltage designs that implement 480 V genera-tors, and step-up transformers are used to parallel with a 12,470 V system and then step-down transformers used to serve fire pump loads. Inrush current must be applied for both the up and the step-down transformers to meet the minimum requirements of 15% voltage drop per NEC 695.7(A).
Single buildings with medium-voltage distribution systems have challenges to comply with the NEC and will require discussions with the authority hav-ing jurisdiction (AHJ) to apply custom designs and applications of equal or bet-ter than the code defined requirements.
There are many options to providing fire pumps for buildings and facilities.
The size and configuration of the facil-ity as well as the intended use will often
dictate the type of pump to use and the quantity needed. When using electric-driven pumps, consideration should be given to how the primary and emergen-cy power supplies are to be arranged and distributed. NFPA standards pro-vide various options to the designer on how to configure the power supplies to ensure the power feeding fire pumps is reliable and is protected. The key for all is to understand the requirements of both NFPA 20 and NFPA 70 to properly choose and configure a fire pump so that the fire protection systems can serve their intended use.
Allyn J. Vaughn is president at JBA Consulting Engineers. He has more than 30 years providing fire protec-tion system design and code consult-ing services, includconsult-ing design and commissioning of fire protection sys-tem for large complex facilities. Rick Reyburn is director of electrical engi-neering and has more than 30 years of experience in development and design of electrical systems and is a licensed professional engineer in more than 30 states.
Figure 5: Vertical and horizontal fire pumps are shown with their associated piping in a high-rise complex.
45
www.csemag.com Consulting-Specifying Engineer • MARCH 2015
Input #100 at www.csemag.com/information
2672 S. La Cienega Bl vd. Los Angeles, C A 90034 USA (800) 336-1942 (310) 839-2828 Fax: (310) 839-6878 www.t ekleen.com inf o@t ekleen.com Scale formation reduces the heat transfer rate and increases the water pressure drop through the heat exchanger and pipes. In fact, one study has shown that .002" fouling will increase pumping needs by 20%.
The Best Engineered Water Filtering Solution Always Costs Less