Chapter 7 of NFPA 110 defines installation requirements for Emergency Power Supply Systems (EPSSs) and makes users aware of environmental conditions that have an effect on the performance of the EPSS. The performance of the EPSS is dependent on many factors, including the installation location and environmental conditions. While NFPA 110 is not a design standard or installation guide for EPSSs, certain minimum standards are recognized as essential for the successful operation of the EPSS.
Design considerations must be made when specifying an EPSS that operates in extreme weather conditions. The EPSS should be protected from floods, fire, vandalism, wind, earthquakes, lightning, and other environmental hazards common to the geographic location. The probability and frequency of these events and the potential to cause a power failure should also be considered.
A good practice is to avoid locating the EPSS equipment (including generators, switchgear, and transfer switches) in building areas subject to flooding. In earthquake prone areas, seismic generator mounts and flexible connections for the fuel-supply system and electrical connections should be considered. Surge arrestors and surge-protection devices should be specified at panels serving sensitive electronic equipment and life-safety loads to protect against lightning strikes or surges that may result from switching inductive loads. Since equipment or cable failure can occur anywhere between the incoming normal service and the load, locating the transfer switch close to the utilization point usually provides greater protection. (7.1.2)
NFPA 110 sets the minimum performance requirements governing the installation of the EPSS equipment. However, the authority having jurisdiction (AHJ) is responsible for enforcing code compliance in a particular city or area and ultimately determines what installations comply with the standard and which codes apply. NFPA 110 is also not intended to allow installations that are contradictory to the equipment manufacturer’s specifications and requirements. (7.1.3)
When the normal power source is not available, the Emergency Power Supply (EPS) shall be permitted to serve optional loads other than emergency system loads, provided that EPS has adequate capacity or automatic selective load pickup and shedding are provided as needed to ensure adequate power to (1) the Level 1 loads, (2) the Level 2 loads, and (3) the optional loads in that order of priority. (7.1.5)
The EPS shall be installed in a separate room for Level 1 installations. The room in which the generator is located must have a two-hour fire resistance rating. NFPA 110 allows but does not require that the EPSS equipment (e.g. transfer switches, circuit breakers, etc.) to be installed in the EPS room. However, it does not allow any other equipment except those that serve this space to be in the EPS room. (7.2.1)
Catastrophic events in the service switchboard could interrupt the EPSS equipment rendering both inoperable. Therefore, Level 1 EPSS equipment is not to be installed in the same room as with the normal service equipment where the service equipment is rated higher than 150V to ground and equal to or greater than 1,000 amps. (7.2.3)
The requirement to provide a separate room does not apply to Level 2 systems that are installed indoors. NFPA 110 also does not restrict Level 2 EPSS equipment from being located in the same room with with Level 1 equipment.
For EPSS equipment located outdoors, the EPS shall be located in a suitable enclosure located outside the building and capable of resisting the entrance of snow or rain at the maximum wind velocity as required by local building codes. EPSS equipment shall be permitted to be installed in the EPS enclosure. However, no other equipment shall be permitted in the EPS enclosure. (7.2.2)
The rooms, enclosures, or separate buildings housing Level 1 or Level 2 EPSS equipment shall be designed to minimize damage from flooding resulting from fire fighting, sewer water backup, and other disasters or occurrences. (7.2.4). If the EPSS equipment is to be located in an area prone to flooding, the authority having jurisdiction (AHJ) may require an elevated structure to place the EPS and EPSS equipment above the 10-year flood plane.
Equipment such as fuel storage tanks and fuel pumps are also subject to the damaging effects of floods and earthquakes and should be taken into consideration by the designers.
The rooms or enclosures containing EPSS equipment shall also be designed to minimize the possibility of damage to the EPSS equipment and permit sufficient room for access for inspection, repair, maintenance, cleaning or replacement.
Anything that is not necessary for the performance of the generator, including cosmetic architecture, should not be installed in the room or enclosure.
For areas where vehicles could hit the equipment, bollards or barricades may need to be installed to prevent damage from an accident.
Maintenance personnel at the generator will be in the dark if primary power is disrupted and the EPS requires attention. A battery-powered emergency light source is required in generator rooms and walk-in enclosures. The emergency lighting charging system and the normal service room lighting shall be supplied from the load side of the transfer switch. (7.3)
Although this lighting requirement does not apply to outdoor units without walk-in access, it may be beneficial to store a flashlight or rechargeable battery powered light at the generator.
Mounting and Vibration
Generators must be installed on solid foundations to prohibit sagging of fuel, exhaust, or lubricating oil piping and damage to parts resulting in leakage at joints. Such foundations shall be raised at least 6 inches above the floor or grade level and permit ease of maintenance. (7.4)
Vibration isolators, as recommended by the manufacturer of the EPS, shall be installed either between the rotating equipment (engine and generator) and its skid base or between the skid base and the foundation or inertia base. (7.5)
Noise and Enclosures
Local codes, the location, and the application itself will dictate the requirements for noise control. Noise treatment, if required, needs to be considered early in the design phase and can add considerable cost and space requirements for the installation. A generator set is a complex noise source that includes the cooling fan noise, the engine noise, and the exhaust noise. Effective noise control must address all of these sources of noise.
Compliance with noise regulations requires an understanding of the ambient noise level and the resultant noise level with the generator set running at full load in those conditions. In general, required noise levels at a property line are often around 60 dBA, while a generator set without any noise reduction can approach 100 dBA. In order to achieve the required noise levels, sound attenuation materials such as exhaust silencers, barriers or ducting to block or change the direction of the noise, and sound absorbing (acoustic) materials may be used to reduce noise.
Sound attenuated enclosures are often provided with generator sets that are installed outdoors. These enclosures effectively form an enclosed space around the generator set and can be fitted with sound absorbing foam and air intake and/or exhaust scoops for redirecting noise and airflow.
Generator sets are almost always provided with an exhaust silencer (muffler) to limit exhaust noise. Silencers are available in several different sound attenuation grades commonly referred to as Industrial, Residential, Critical, and Hospital and can reduce exhaust noise from 12-40 dB. Care must be taken when choosing exhaust silencers so as not to create excessive airflow restriction and exhaust backpressure.
When an EPS is installed in an outdoor enclosure, NFPA 110 requires that the enclosure resists the entrance of snow and rain and allows EPSS equipment to be mounted within the EPS enclosure. It also specifies that the design shall include consideration of noise control regulations. (7.6)
A generator installed in an outdoor enclosure with base-mounted fuel tank may raise the generator access doors to a point that maintenance is not possible without a ladder. In these instances, a raised platform with a minimum width of 36 inches from the generator rails must be installed with railings and stairs to allow full access to the maintenance doors.
Heating, Cooling, and Ventilating
For generators located indoors, ventilation must be considered. Heat from the engine, radiator, alternator, and exhaust system could raise the operating temperature of the equipment and must be vented to obtain proper room temperature. Design of an EPS ventilation system should consider the following:
- Radiator airflow (when installed in the EPS room)
- Combustion airflow consumed by the engine
- Maximum potential ambient temperature of air entering the EPS room for ventilation
- Radiated heat load from the EPS
- Radiated heat load from the EPS exhaust system
- Other heat loads in the room
- Maximum allowed airflow pressure drop through the ventilation supply into the room and through the ventilation discharged from the radiator
Air for engine combustion airflow requirements shall be installed per the manufacturer requirements. Ventilation air for the EPS must be direct from outside in a 2-hour enclosure for Level 1 installations to maintain the 2-hour fire rating required by NFPA 110. The outside airflow must be designed for the rated load of the EPS. Fire dampers, shutters, or other self-closing devices shall not be permitted in ventilation openings or ductwork in a Level 1 installation. Motor operated dampers, when used, shall be spring operated to open and motor closed. (7.7)
Level 1 installations in outdoor enclosures shall be maintained at not less than 40 degrees F. Depending on the local climate, this may require motor operated dampers and auxiliary heaters for the enclosure in addition to the water jacket heater required by NFPA 110.
Exterior louvers must be designed for prevailing winds that might blow against the radiator fan discharge air.
Makeup water hose bibs and floor drains, where required by other codes and standards, shall be installed in EPS equipment rooms. Generators with unit mounted radiators must be connected to the exterior louvers by means of flexible sections. (7.8)
NFPA 110 requires that the EPS and its fuel supply are required to be sufficient to supply the loads served by the EPSS for its specified time (class of service) without having to refuel.
All fuel tanks and systems shall be installed and maintained in accordance with NFPA 30, Flammable and Combustible Liquids Code; NFPA 37, Standard for the Installation and Use of Stationary Combustion Engines and Gas Turbines; NFPA 54, National Fuel Gas Code; and NFPA 58, Liquefied Petroleum Gas Code. (18.104.22.168)
The fuel system design shall provide for a supply of clean fuel to the prime mover (engine). (22.214.171.124) Without a clean supply of fuel the generator will not function. This covers more than the quality of the fuel. Designers should also consider the placement and protection of the fuel system to allow the EPS to function after a flood or an earthquake.
Tanks shall be sized so that the fuel is consumed within the storage life, or provisions shall be made to remediate fuel that is stale or contaminated or to replace stale or contaminated fuel with clean fuel. (126.96.36.199) Fuel quality and fuel management are concerns because many generator failures are attributed to poor fuel quality, contamination, or other fuel problems.
Fuel tanks shall be close enough to the prime mover (engine) for the fuel lift (suction head) of the prime mover fuel pump to meet the fuel system requirements, or a fuel transfer pump and day tank shall be provided. (7.9.2) The location of the main fuel tank is not specified, nor are overhead fuel supplies prohibited. This allows flexibility in the design and installation of the system. However, if these values are exceeded a day tank arrangement is required.
Approved flexible fuel lines shall be used between the prime mover (engine) and the fuel piping. Galvanized fuel lines shall not be used. (7.9.3) The reaction between sulfur in the diesel fuel and the galvanizing on the interior of the piping could adversely affect engine performance.
Day tanks on diesel systems shall be installed below the engine fuel return elevation and the return line shall be below the fuel return elevation. Gravity fuel return lines between the day tank and the main supply tank shall be sized to handle the potential fuel flow and shall be free of traps so that fuel can flow freely to the main tank. (7.9.4) The intent of this requirement is to allow the fuel from the engine to return to the day tank without the use of a fuel pump and prevent possible failure points and fuel leaks.
Integral tanks, such as sub-base or belly tanks, are limited to 660 gallons of diesel fuel inside buildings or on rooftops. (7.9.5) It is not a requirement to provide integral tanks for generators installed on roofs and in basements.
For gaseous fueled systems, where the gas supply is connected to the building gas supply system, it shall be connected on the supply side of the main gas shutoff valve and marked as supplying an emergency generator. (7.9.6) When firefighters respond to a fire, they shut off the main gas supply to a building. Shutting off the main valve would inadvertently turn off the fuel supply to the emergency generator, leaving the EPS without fuel.
One of the more controversial requirements of NFPA 110 is the requirement for 96 hours of fuel capacity for Level 1 systems. For health care facilities, the Joint Commission has clarified that the intent is to have a plan for providing 96 hours of fuel capacity, not to have a 96-hour onsite storage capacity. Local fuel suppliers must be reliable and able to provide a plan to certify this will be provided. When using a refueling plan with a listed generator sub-base secondary containment fuel tank that is 660 gallons or less, the tank may be installed outdoors or indoors without diking or remote impounding unless the authority having jurisdiction (AHJ) states otherwise.
The 2016 edition of NFPA 110 includes a new requirement that prohibits the use of automatically actuated valves in the fuel supply and return lines. (7.9.13) This requirement is intended to reduce the chances for inadvertent interruption of the fuel supply and EPS to fire pumps and other life safety equipment during a fire.
NFPA 110 requires that the exhaust system equipment and installation, including piping, muffler and related accessories, shall be in accordance with NFPA 37, Standard for the Installation and Use of Stationary Combustion Engines and Gas Turbines; and other applicable standards. (7.10.1)
Exhaust piping shall be connected to the prime mover (engine) by means of a flexible connector and shall be independently supported thereafter so that no damaging weight or stress is applied to the engine exhaust manifold or turbocharger. (7.10.3) Flexible connectors for exhaust piping are typically supplied by the generator set manufacturer.
A condensate trap and drain valve shall be provided at the low points of the piping unless the piping is self-draining. (188.8.131.52)
For reciprocating engines, mufflers shall be placed as close as practicable to the engine, in a horizontal position if possible. (184.108.40.206)
An approved thimble shall be used where exhaust piping passes through combustible walls or partitions. (220.127.116.11)
For reciprocating engines, the piping shall terminate in any of the following: (18.104.22.168)
- Rain Cap;
- Ell, pointing downwind from the prevailing wind
- Vertically upward-orient stack with suitable provisions for trapping and draining rain and snow water.
Consider the heat effects of exhaust piping placed near conduit runs, fuel piping, and lighting fixtures. (22.214.171.124)
Design consideration shall be given to insulating the engine exhaust system in buildings after the flexible section. (126.96.36.199)
Exhaust systems shall be designed and installed to meet the requirements of the manufacturer and eliminate excessive backpressure on the engine by properly selecting, routing and installing the piping size, connections and muffler. (7.10.4)
NFPA 110 requires that the room in which the EPS equipment is located shall not be used for other purposes that are not directly related to the EPS. (7.11.1) Parts, tools and manuals for routine maintenance and repair are permitted to be stored in the generator room. However, setting up an office in the room would violate this requirement.
NFPA 110 does not mandate the use of a fire suppression system in the generator room, nor does it require a fire detection system or address whether it is permissible to install smoke or heat detection systems in lieu of a fire suppression system. Rather it references, NFPA 72, National Fire Alarm and Signaling Code, when a fire detection system is installed.
The installation of a lightning protection system is not required, but NFPA 780, Standard for the Installation of Lightning Protection Systems, must be followed for the installation of such a system.
In recognized seismic areas, the generator and other EPSS components, such as electrical distribution lines, water lines, fuel lines, transfer switches, distribution panels, circuit breakers, and other components shall be designed and installed to minimize damage from earthquakes. ASCE / SEI 7, Minimum Design Loads for Buildings and Other Structures, provides information regarding earthquakes with maps indicating the regions affected by them.
NFPA 110 requires that the distribution and wiring systems within the EPSS shall be installed in accordance with NFPA 70, National Electrical Code (NEC). When EPSSs are installed in health care facilities, the installation of the EPSS shall also be in compliance with NFPA 99, Health Care Facilities Code. (7.12)
Where two standards are applicable for a given installation, the most stringent requirement for either document typically applies to the installation.
The wiring between the generator output terminals and the first distribution overcurrent protective device (OCPD) terminals shall be located at a minimal distance to ensure system reliability and safety. (7.12.3)
Flexible conduit sections shall be installed between the generator and the transfer switch, the control and annunciator panels, and any accessory such as jacket water heaters. (7.12.4) Stranded wire of adequate size shall be used to minimize breakage due to vibration and bushings shall be installed to protect wiring from abrasion with conduit terminations. (188.8.131.52)
All AC powered support and accessory equipment shall be supplied from the load side of the ATS or the output terminals of the generator set ahead of the main circuit breaker to ensure continuity of the EPSS operation and performance. This equipment could include such items as fuel transfer pumps, battery chargers, and jacket water cooling pumps. (7.12.5)
The starting batteries shall be located next to the engine starter to minimize voltage drop. (7.12.6) Battery cables shall be sized to minimize voltage drop in accordance with the manufacturer’s recommendations and accepted engineering practices. (184.108.40.206)
Battery charger output wiring shall be permanently connected to the primary side of the starter solenoid (positive) and the generator set frame (negative), or other grounding location. (220.127.116.11) A permanent connection away from the battery terminals is necessary to remove the corrosion problem that may occur at the battery terminals.
When all of the installation standards are met, failures that are due to improper installations are reduced greatly.