1 Scope
NOTE This specification covers packaged engine-generator sets and their accessories for emergency, legally required standby, and optional standby power service in accordance with NFPA 70 Articles 700, 701, and 702, and NFPA 110. (1.1)
NOTE Each set comprises a reciprocating internal combustion engine, a directly coupled synchronous alternator, a unit-mounted controller, batteries and charging system, cooling and exhaust systems, fuel system, and an enclosure or base, furnished as a single integrated assembly listed to UL 2200. (1.2)
NOTE The performance commitments in this standard assume those coordinated scopes are in place. (1.4)
NOTE This standard does not cover prime power generation in continuous duty service. (1.5)
NOTE Prime and continuous duty ratings per ISO 8528 imply different engine selection, cooling, fuel infrastructure, and maintenance assumptions and are outside scope. (1.5.1)
NOTE This standard does not cover paralleled multi-engine plants beyond the basic provisions needed to add a future paralleling cubicle. (1.6)
1.6.1 Full paralleled systems with load sharing, synchronizing, and utility paralleling per IEEE 1547 require additional engineering and shall be specified separately.
2 Referenced Standards
2.1 Equipment, materials, and installation shall comply with the latest adopted edition of the standards listed below.
| Standard |
Title |
| NFPA 110 |
Standard for Emergency and Standby Power Systems |
| NFPA 37 |
Standard for the Installation and Use of Stationary Combustion Engines and Gas Turbines |
| NFPA 30 |
Flammable and Combustible Liquids Code |
| NFPA 54 |
National Fuel Gas Code |
| NFPA 58 |
Liquefied Petroleum Gas Code |
| NFPA 70 |
National Electrical Code (Articles 445, 700, 701, 702, 705) |
| NFPA 70E |
Standard for Electrical Safety in the Workplace |
| UL 2200 |
Stationary Engine Generator Assemblies |
| UL 142 |
Steel Aboveground Tanks for Flammable and Combustible Liquids |
| UL 2085 |
Protected Aboveground Tanks for Flammable and Combustible Liquids |
| UL 1236 |
Battery Chargers for Charging Engine-Starter Batteries |
| ISO 8528 |
Reciprocating Internal Combustion Engine Driven Alternating Current Generating Sets |
| ISO 3046 |
Reciprocating Internal Combustion Engines — Performance |
| IEEE 446 |
Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications (Orange Book) |
| IEEE 1547 |
Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces |
| NEMA MG 1 |
Motors and Generators |
| EGSA 100B |
Performance Standard for Engine Cranking Batteries |
| EGSA 101P |
Performance Standard for Engine Driven Generator Sets, Prime Mover |
| EGSA 109C |
Code of Practice for Packaged Engine Generator Sets |
| 40 CFR Part 60 Subpart IIII |
Standards of Performance for Stationary Compression Ignition Internal Combustion Engines |
| 40 CFR Part 60 Subpart JJJJ |
Standards of Performance for Stationary Spark Ignition Internal Combustion Engines |
| 40 CFR Part 63 Subpart ZZZZ |
NESHAP for Stationary Reciprocating Internal Combustion Engines |
| 40 CFR Part 1039 |
Control of Emissions from New and In-Use Nonroad Compression-Ignition Engines (Tier 4) |
| ASCE 7 |
Minimum Design Loads and Associated Criteria for Buildings and Other Structures |
| IBC |
International Building Code (seismic and anchorage provisions) |
| ICC ES AC156 |
Acceptance Criteria for Seismic Certification by Shake-Table Testing |
| NETA ATS |
Acceptance Testing Specifications for Electrical Power Equipment and Systems |
2.2 Where the contract documents, the adopted building code, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
3 Submittals
3.1 Action Submittals
3.1.1 Contractor shall submit the following for the Engineer's review prior to procurement and fabrication:
- Product data for the generator set, alternator, controller, battery charger, jacket water heater, enclosure, sub-base fuel tank, exhaust silencer, and all factory-supplied accessories
- Dimensioned shop drawings showing plan, elevations, conduit and cable entry locations, fuel piping connections, exhaust outlet location, cooling air intake and discharge openings, and required clearances
- Single-line diagram showing the generator output, neutral treatment, main line breaker, instrument transformers, and control wiring interfaces with the transfer switch
- Alternator reactance data, decrement curve, and starting kVA / voltage dip analysis for the project's largest motor and step-load profile
- Site-specific exhaust emissions calculation and compliance documentation for the applicable EPA standard and any state or local air quality permit
- Sound data showing octave-band sound pressure and overall A-weighted level at 7 m at full load, and predicted sound at the nearest property line or sensitive receptor
- Fuel consumption table at 25%, 50%, 75%, and 100% rated load, and calculated runtime at the specified tank capacity
- Cooling system performance data at the design ambient temperature, including air flow, static pressure available for ductwork, and radiator restriction limits
- Seismic certification documentation per ICC ES AC156 or per the project's applicable importance factor
- Genset controller submittal showing NFPA 110 compliance, all configured alarms and shutdowns, and the remote annunciator point list
- Factory test certificates (production tests per UL 2200 and ISO 8528) and the proposed factory witness test procedure
☑ Product data for generator and accessories
☐ Dimensioned shop drawings
☐ Single-line diagram and control interfaces
☐ Alternator reactance and starting kVA analysis
☐ Emissions compliance documentation
☐ Sound data at 7 m and at property line
☐ Fuel consumption and runtime calculation
☐ Cooling performance at design ambient
☐ Seismic certification (AC156)
☐ Controller submittal and annunciator point list
☐ Factory test plan and certificates
3.1.2 Fabrication shall not proceed until the action submittals are reviewed and returned.
3.2 Closeout Submittals
3.2.1 Contractor shall provide the following at substantial completion before the generator is accepted into emergency or standby service:
- Operation and maintenance manuals, indexed, including engine, alternator, controller, battery charger, and all accessories
- As-built drawings reflecting installed conduit and fuel pipe routing, exhaust routing, and any field changes
- Signed and dated NFPA 110 acceptance test record, including the on-site installation test and any required load bank test
- Factory and field test reports, including infrared scan of all power terminations under load
- Emissions source test report, where required by the air quality permit
- Warranty documentation and the start of the warranty period (commencement date)
- Spare parts inventory list with manufacturer part numbers
- Owner training sign-off sheet documenting training topics and attendees
☑ Operation and maintenance manuals (indexed)
☐ As-built drawings (conduit, fuel, exhaust routing)
☑ Signed NFPA 110 acceptance test record
☐ Factory and field test reports with infrared scan
☐ Emissions source test report (where required)
☑ Warranty documentation with commencement date
☐ Spare parts inventory list with part numbers
☐ Owner training sign-off sheet
4 Quality Assurance
4.1 Manufacturer Qualifications
4.1.1 The generator set shall be manufactured by a single company responsible for the engine selection, alternator selection, controller, base/enclosure, and integration.
4.1.2 The manufacturer shall have a minimum of ten years documented experience producing UL 2200 listed engine-generator sets in the rating range of the project.
4.1.3 The manufacturer shall maintain an ISO 9001 certified quality management system.
4.1.4 A factory-authorized service organization shall be located within a service radius such that a field technician with parts can be on site within four hours of notification, 24 hours a day, throughout the warranty period.
NOTE Local service capability is critical for life safety applications; a fast unit price from a manufacturer without local service is a false economy when the set fails during an outage. (4.1.5)
4.2 Source Limitations
4.2.1 The complete set — engine, alternator, base, controller, battery charger, enclosure, sub-base tank where provided, and exhaust silencer — shall be furnished by the generator manufacturer as an integrated assembly listed to UL 2200.
4.2.2 Component-by-component assembly by the installing Contractor is not acceptable.
NOTE UL 2200 listing depends on the integrated assembly and not on the components individually. (4.2.3)
4.3 Listing and Labeling
4.3.1 The complete generator set assembly shall be listed and labeled to UL 2200 by a Nationally Recognized Testing Laboratory.
4.3.2 The sub-base fuel tank, where provided, shall be listed and labeled to UL 142 or UL 2085 as applicable.
4.3.3 The battery charger shall be listed to UL 1236.
4.3.4 The controller and its protective relaying shall be listed for the purpose.
4.4 Testing Personnel Qualifications
4.4.1 Field acceptance testing and commissioning shall be performed by technicians certified by NETA, EGSA, or the generator manufacturer's training program.
4.4.2 Personnel performing NFPA 110 installation acceptance testing shall have documented experience commissioning at least three sets of the same general type and rating class.
5 Environmental and Service Conditions
5.1 The generator set shall be suitable for continuous operation, under the engine duty class selected, at the site's ambient conditions.
5.2 Where site conditions exceed the standard rating basis, the set shall be derated per ISO 8528 and the alternator and engine selected accordingly.
NOTE The rating shall be confirmed against the site's design ambient. (5.3)
NOTE Standard rating conditions per ISO 8528 are 25 deg C ambient, 100 m altitude, 30 percent relative humidity, and 100 kPa barometric pressure; very few real sites match this basis exactly. (5.3.1)
5.4 Ambient Temperature
40 deg C (standard outdoor enclosure rating)
45 deg C (warm climate)
50 deg C (hot climate or rooftop)
55 deg C (extreme heat)
5.4.1 The cooling system shall be selected so that the engine coolant and after-cooler air temperatures remain within the engine manufacturer's limits at the design ambient with the set carrying its rated load.
5.4.2 Radiator-cooled sets shall be sized for the air temperature rise through the enclosure plus the design ambient.
5.5 Altitude
Below 500 ft (150 m) - no derating
500 to 3,300 ft (150 to 1,000 m) - verify engine derating
3,300 to 6,600 ft (1,000 to 2,000 m) - engine derating required
Above 6,600 ft (2,000 m) - consult engine manufacturer
5.5.1 The published kW rating shall be the derated output at the design altitude and ambient, not the standard-condition rating.
NOTE Naturally aspirated diesel engines lose roughly 3 percent of power per 300 m above 150 m, and additional derating applies above the engine manufacturer's threshold ambient; turbocharged engines hold output longer but eventually derate as well. (5.5.2)
5.6 Cold Weather Service
Above 0 deg C (warm climate)
0 to -10 deg C
-10 to -25 deg C
Below -25 deg C (arctic)
5.6.1 Where the design minimum temperature is at or below 0 deg C, cold weather start aids shall be provided as specified in the Engine and Batteries sections.
NOTE NFPA 110 requires Level 1 systems to be capable of starting within 10 seconds of receiving a start signal; meeting this in cold weather requires a properly sized jacket water heater, battery heater pad, and (for very cold climates) lube oil heating. (5.6.2)
5.7 Corrosive and Coastal Environments
5.7.1 Where the set is installed within 1 mile of a salt water shoreline, in heavy industrial atmospheres, or in chemically aggressive environments, the enclosure paint system, fasteners, and exposed metal components shall be specified for the corrosivity category.
5.7.2 Stainless steel hardware should be substituted for plated steel at exterior fasteners.
5.7.3 The enclosure shall receive an enhanced paint system as described under Enclosure.
6 Ratings
6.1 Continuous Output Rating (kW)
302000
306010015020030040050060075010001250150017502000
Default: 500 kW
Per drawings
6.1.2 The Engineer shall provide both the standard-condition rating and the site-rated kW on the schedule.
NOTE The site-rated kW is the value that matters for connected-load sizing; it is the kW the set will actually deliver after derating for altitude, ambient, and any fuel selection (for example, the natural-gas rating of a dual-fuel engine is generally lower than its diesel rating). (6.1.3)
6.2 Duty Class
● Emergency Standby Power (ESP) - variable load, limited hours
○ Limited-Time Prime (LTP) - constant load, limited annual hours
○ Prime Power (PRP) - variable load, unlimited hours
○ Continuous Operating Power (COP) - constant load, unlimited hours
NOTE For a building emergency or standby system per NFPA 110, the Emergency Standby Power (ESP) rating is appropriate; it permits a variable load with average load not exceeding 70 percent of ESP and limited annual run hours. (6.2.1)
NOTE Specifying Prime or Continuous for a building standby application over-sizes the set and increases first cost without operational benefit; Prime and Continuous duty classes are appropriate for sets that run as the principal power source. (6.2.2)
6.3 Output Voltage and Configuration
208Y/120V, 3-phase, 4-wire
240/120V, 1-phase, 3-wire
240 delta / 120V, 3-phase, 4-wire (high-leg)
480Y/277V, 3-phase, 4-wire
600Y/347V, 3-phase, 4-wire
6.3.1 The selected voltage shall match the transfer switch and downstream distribution.
NOTE For commercial and institutional buildings 100 kW and above, 480Y/277V three-phase four-wire is the standard selection because it minimizes feeder copper between the set and the transfer switch; 208Y/120V is appropriate for smaller buildings whose entire distribution is 208Y/120V. (6.3.2)
6.4 NFPA 110 Classification
NOTE NFPA 110 classifies emergency and standby power systems by Level, Type, and Class. (6.4.1)
● Level 1 (failure to perform could result in loss of human life or serious injury)
○ Level 2 (less critical to human life and safety)
Type 10 (10 seconds)
Type 60 (60 seconds)
Type 120 (120 seconds)
Type U (uninterruptible)
Class 2 (2 hours)
Class 6 (6 hours)
Class 8 (8 hours)
Class 24 (24 hours)
Class 48 (48 hours)
Class 96 (96 hours)
NOTE The combination of Level, Type, and Class drives controller requirements, fuel storage, testing, and maintenance; Level 1 systems serve loads where failure to perform could result in loss of human life or serious injury, and Level 2 systems serve loads less critical to human life. (6.4.2)
6.4.3 For NFPA 70 Article 700 emergency systems, Type 10 is the minimum and shall be confirmed on commissioning.
NOTE Type 60 and Type 120 are appropriate for legally required standby and optional standby loads where a longer interruption is acceptable; Type U (uninterruptible) is generally achieved by combining the generator with a UPS that bridges the engine start interval, and the generator alone is not Type U. (6.4.4)
6.4.5 The project's Class shall be the larger of the value required by the AHJ and the value required by the served occupancy.
NOTE Healthcare facilities under NFPA 99 commonly require Class 96, and common-use buildings often default to Class 8. (6.4.6)
7 Engine
7.1 The engine shall be a four-stroke, water-cooled, reciprocating internal combustion engine rated by the engine manufacturer for use in stationary engine-generator service, complying with ISO 3046.
7.2 The engine shall be selected so that, at the alternator's rated output and power factor at the site conditions, the engine operates within its continuous rating for the selected duty class.
7.3 Fuel
● Diesel (No. 2 ULSD)
○ Natural gas
○ Liquefied petroleum (LP) gas
○ Bi-fuel (diesel primary, natural gas supplement)
○ Dual-fuel (natural gas or diesel, selectable)
7.3.1 The Engineer shall confirm the AHJ's position before selecting natural gas for a Level 1 system.
NOTE Diesel No. 2 ultra-low sulfur (ULSD) is the default for sets serving NFPA 110 Level 1 systems because the on-site fuel inventory provides predictable runtime independent of the gas utility; natural gas eliminates on-site fuel storage but ties the set's availability to the gas utility, which is not always acceptable for life-safety loads in seismic or high-wind regions. (7.3.2)
7.3.3 Combustion Air
7.3.3.1 The engine shall be furnished with a dry-type air cleaner sized for the engine's full-load air flow and the design ambient air quality.
7.3.3.2 Combustion air shall be drawn from outside the enclosure for sound-attenuated and walk-in enclosures, with a service indicator showing filter restriction.
7.4 Engine Mechanical Components
7.4.1 Each engine shall be furnished with a lube oil cooler, full-flow lube oil filtration, fuel filtration with water separation (for diesel), thermostatically controlled coolant, a flexible exhaust connection, and a starter motor sized for the engine and the design minimum temperature.
7.5 Emissions
Tier 2 (legacy installations only)
Tier 3
Tier 4 Interim
Tier 4 Final
○ 40 CFR Part 60 Subpart JJJJ (emergency rating)
○ 40 CFR Part 60 Subpart JJJJ (non-emergency rating)
● Not applicable (diesel engine)
7.5.1 Diesel engines installed in stationary service shall comply with the applicable subpart of 40 CFR Part 60 (Subpart IIII for compression-ignition) at the manufacturing date of the engine, and with 40 CFR Part 63 Subpart ZZZZ for in-use operation where applicable.
7.5.2 Spark-ignition engines on natural gas or LP shall comply with 40 CFR Part 60 Subpart JJJJ.
7.5.3 Where the AHJ or air permit authorizes a lower tier for emergency-only service, the documentation supporting the lower tier shall be included with the submittal.
NOTE New compression-ignition engines manufactured to current standards meet EPA Tier 4 Final for the regulated power range under 40 CFR Part 1039. (7.5.4)
NOTE Tier 4 Final compliance for diesel engines in the typical commercial size range generally requires aftertreatment — diesel oxidation catalyst, diesel particulate filter, and/or selective catalytic reduction with urea (DEF) injection — depending on engine size and the engine manufacturer's certification pathway, and the aftertreatment imposes physical space, exhaust temperature, and consumable handling requirements that shall be coordinated early. (7.5.5)
7.5.6 Annual Run-Hour Limitations
7.5.6.1 The Engineer shall confirm the project's permit limits and document them in the O&M manual.
NOTE EPA emergency-engine designations cap non-emergency operating hours, typically at 100 hours per year for maintenance and testing combined, with further restrictions on emergency demand response participation; exceeding the limit re-classifies the engine and triggers additional emission control requirements that may not be practical to add after installation. (7.5.6.2)
7.6 Start Aids
7.6.1 Jacket Water Heater
● Required (NFPA 110 Type 10 or colder than 0 deg C)
○ Not required (warm climate, slower Type)
7.6.1.1 A thermostatically controlled jacket water heater shall be provided to maintain engine coolant temperature at a value that allows reliable starting within the NFPA 110 Type time.
7.6.1.2 Heater wattage shall be sized for the engine displacement and the design minimum ambient.
7.6.1.3 Power for the heater shall be from a dedicated branch circuit on the normal source so that the heater is energized whenever the engine is not running.
7.6.2 Battery Heater Pad
● Required (design minimum below 0 deg C)
○ Not required (warm climate)
7.6.2.1 Where the design minimum temperature is below 0 deg C, a thermostatically controlled battery heater pad shall be provided so that cranking capacity is preserved.
NOTE Lead-acid battery cranking capacity drops sharply below 0 deg C, and an unheated battery in a cold enclosure may not crank a cold engine within 10 seconds. (7.6.2.2)
7.6.3 Lube Oil Heater
○ Required (design minimum below -15 deg C)
● Not required
7.6.3.1 In design minimum conditions below -15 deg C, or where the engine manufacturer requires it, a lube oil heater shall be provided.
NOTE Cold lube oil increases cranking torque and lengthens start time; the heater maintains the oil at a temperature that allows the engine to crank and accept load within the required time. (7.6.3.2)
8 Alternator
8.1 The alternator shall be a brushless, salient pole, synchronous machine with rotating field and permanent magnet generator (PMG) excitation, conforming to NEMA MG 1, Part 32, and rated for the selected duty class per ISO 8528.
8.2 The alternator shall be directly coupled to the engine through a flexible coupling on a common skid.
8.3 Belt-driven or remote-coupled alternators are not acceptable.
8.4 Excitation
● Permanent magnet generator (PMG) excitation
○ Shunt excitation
NOTE PMG excitation provides reliable short-circuit current for a defined time (typically 300 percent of rated current for 10 seconds) and is recommended for any set whose loads include selective coordination requirements or large motor starting; shunt excitation collapses field current under a bolted fault and cannot reliably trip downstream overcurrent devices, which is a significant safety and selectivity issue. (8.4.1)
8.5 Insulation Class and Temperature Rise
○ Class H insulation, Class H temperature rise
● Class H insulation, Class F temperature rise (recommended)
○ Class F insulation, Class B temperature rise
NOTE Specifying Class H insulation with a Class F temperature rise is the industry recommended practice because the insulation life is materially extended by operating at a lower temperature than its limit. (8.5.1)
8.6 Voltage Regulation
8.6.1 The voltage regulator shall be electronic, with three-phase RMS sensing, and shall maintain steady-state voltage regulation within ±0.5 percent of rated voltage over no-load to full-load and 0.8 lagging to unity power factor.
8.6.2 The regulator shall include a volts-per-hertz limiter to protect the alternator and connected loads on underspeed, an overvoltage limiter, and a separately adjustable underfrequency knee.
Standard (per manufacturer)
Low reactance (for stiff system / motor starting)
1035
101520253035
Default: 25 percent
8.7.1 Voltage dip during the worst case starting step (typically the largest fire pump or chiller) shall not exceed the value selected.
8.7.2 The submittal shall include a starting kVA / voltage dip analysis demonstrating compliance.
8.7.3 The Engineer shall verify both the voltage dip during the largest motor start and the short-circuit current rating of downstream equipment before selecting a low reactance alternator.
NOTE Low reactance alternators reduce voltage dip during motor starting at the cost of higher available short-circuit current, which the downstream equipment must be rated to interrupt. (8.7.4)
9 Controller
9.1 The genset controller shall be a microprocessor-based unit, listed for the purpose, mounted on the generator set with a vibration-isolated bracket, with an alphanumeric or graphical display visible from the set's normal service position.
9.2 The controller shall be NFPA 110 compliant for the project's Level and Type, providing all required alarms, shutdowns, and metering.
9.3 Required Functions
9.3.1 The controller shall provide as a minimum the following functions:
- Cranking and starting per the selected NFPA 110 Type
- Cool-down cycle on transfer back to normal (engine continues to run unloaded for a programmable period)
- Generator output metering (voltage, current, kW, kVAR, kVA, kWh, power factor, frequency, and run hours)
- Engine instrumentation (oil pressure, coolant temperature, battery voltage, fuel level)
- Programmable exerciser to start and (optionally) load the set on a periodic schedule
- Programmable cool-down and warm-up times
- Alarm log and event history with date and time stamp
- Communication interface (Modbus TCP/IP at a minimum) for integration with the building management system
Modbus RTU (RS-485)
Modbus TCP/IP (Ethernet)
BACnet IP
DNP3
Multiple protocols (specify in submittal)
9.4 NFPA 110 Alarms and Shutdowns
● Level 1 full alarm/shutdown set per NFPA 110 Table 4.7.3
○ Level 2 alarm/shutdown set
9.4.1 The controller shall be configured for the full alarm and shutdown set required by the project Level.
NOTE For Level 1 systems, NFPA 110 Table 4.7.3 requires specific alarms and shutdowns including overcrank, low coolant temperature, high coolant temperature pre-alarm and shutdown, low oil pressure pre-alarm and shutdown, overspeed shutdown, low fuel pre-alarm, low coolant level, battery charger malfunction, low battery voltage, and EPS supplying load. (9.4.2)
9.5 Remote Annunciator
Per drawings (deferred by default)
● Dedicated copper run from controller (two separate raceways for Level 1)
○ Network-attached (IP) annunciator with redundant link
9.5.1 A remote annunciator shall be provided per NFPA 110 4.6.4 at a location continuously monitored, normally outside the generator room — typically at the building's fire command center, security desk, or facility operations room.
9.5.2 The annunciator shall display all required NFPA 110 alarms with a common audible alarm, a means to silence the audible, and a means to test the lamps.
9.5.3 NFPA 110 requires the wiring from the controller to the annunciator to be supervised.
NOTE The most common implementation is a dedicated copper run; a network-attached annunciator is acceptable where the network meets the supervision requirements and the network is itself supplied from the standby system. (9.5.4)
9.6 Main Line Circuit Breaker
○ Thermal-magnetic (smaller sets)
● Electronic LSI (Long-time, Short-time, Instantaneous)
○ Electronic LSIG (with ground fault)
9.6.1 A main line circuit breaker shall be provided on the generator set output per NEC 445.18, sized for the alternator's rated output.
9.6.2 The breaker shall be molded case or insulated case as appropriate, with a thermal-magnetic or electronic trip unit, and shall be field-accessible for maintenance and testing.
10 Cooling System
10.1 The cooling system shall be sized for the engine's full-load heat rejection at the site design ambient, with the air flow path that the enclosure or room imposes.
● Unit-mounted radiator (set-mounted, engine-driven fan)
○ Remote radiator (separate radiator, set-mounted heat exchanger)
○ City water (heat exchanger to building cooling system)
10.2 City-water cooling shall not be used for NFPA 110 Level 1 systems because the cooling source must remain available during the same events that may have caused the outage.
NOTE The default arrangement is a unit-mounted radiator with a blower fan driven by the engine, drawing air from one face of the enclosure and discharging through the radiator; for very large sets, sets in walk-in enclosures with sound attenuation, or sets inside buildings without acceptable air flow, a remote radiator or heat exchanger arrangement may be required. (10.3)
10.4 Radiator
● Engine-driven (belt or direct)
○ Electric (separately driven)
50/50 ethylene glycol / water
Propylene glycol / water (50/50)
Manufacturer's pre-mixed inhibited coolant
10.4.1 The radiator shall be sized for the engine manufacturer's published heat rejection at the site ambient with at least 10 deg C margin on coolant outlet temperature.
10.4.2 Radiator core construction shall be copper-brass or aluminum, with corrosion protection appropriate to the environment.
10.4.3 Aluminum cores in salt air shall not be specified.
10.5 Coolant Recovery and Make-up
10.5.1 A coolant recovery bottle shall be provided so that overflow on thermal expansion does not result in coolant loss.
10.5.2 For unattended sets or sets in remote locations, a low coolant level pre-alarm shall be wired to the controller and the remote annunciator.
11 Fuel System
11.1 Diesel Fuel Storage
○ Sub-base tank (UL 142, single-wall)
● Sub-base tank (UL 142, double-wall with interstitial monitoring)
○ Protected sub-base tank (UL 2085, two-hour fire rated)
○ External aboveground tank with day tank at generator
○ Underground tank with day tank at generator
11.1.1 Sub-Base Fuel Tank
NOTE The default fuel storage configuration is a sub-base tank — a fuel tank constructed as the base of the generator set, listed to UL 142, with interstitial monitoring on double-wall designs. (11.1.1.1)
504000
50100250500100015002000250030004000
Default: 1000 gal
Per drawings
○ Single-wall steel (UL 142)
○ Double-wall steel with interstitial space (UL 142)
● Double-wall with interstitial leak detection sensor
○ Concrete-encased UL 2085 (two-hour fire rated)
NOTE Sub-base tanks are practical up to roughly 4,000 gallons (15,000 liters); larger storage typically requires an external bulk tank with a smaller day tank at the set. (11.1.1.2)
11.1.1.3 The tank capacity shall provide the NFPA 110 Class runtime at the alternator's full-load fuel consumption.
11.1.1.4 The submittal shall include a fuel consumption table at 25, 50, 75, and 100 percent load and the calculated runtime so that the Engineer can confirm that the selected tank meets the Class requirement.
NOTE Double-wall construction with interstitial leak detection is the default because it provides secondary containment without requiring a separate concrete or steel dike, and the leak detector provides early warning of either a primary tank failure or condensation in the interstitial space; single-wall tanks require a separate containment basin sized for the tank capacity per NFPA 30. (11.1.1.5)
11.1.1.6 The tank shall be furnished with normal and emergency vents per NFPA 30, a fill connection with overfill protection per NFPA 30, a level indicator readable without opening the tank, a low-fuel pre-alarm contact wired to the controller, and a fuel return port.
11.1.1.7 Interconnection between an external tank and a day tank shall include a transfer pump, day tank float controls, and an overflow return to the bulk tank.
11.1.2 Fuel Quality
11.1.2.1 Diesel fuel shall be ultra-low sulfur (ULSD), No. 2-D per ASTM D975, with a cold-flow point suitable for the climate.
11.1.2.2 The Owner's operating instructions shall include a fuel quality program: at minimum, quarterly testing for water, particulates, and microbial growth, and a fuel polishing program for sets stored at high fill levels for extended periods.
11.2 Natural Gas and LP Supply
Low pressure (less than 1 psig)
Medium pressure (1 to 5 psig)
Elevated pressure (5 to 15 psig)
Per engine manufacturer requirement
11.2.1 Where the set is fueled by natural gas or LP, the supply piping shall comply with NFPA 54 (natural gas) or NFPA 58 (LP), be sized for the engine's full-load fuel demand at the worst-case supply pressure, and terminate with a manual shutoff valve and a flexible connector at the engine.
11.2.2 A solenoid valve interlocked with the controller shall close on engine shutdown.
11.2.3 The supply pressure at the engine inlet, with the engine at full load, shall remain within the manufacturer's required range.
11.2.4 The supply piping shall be sized with margin and verified at commissioning.
NOTE Inadequate gas supply pressure at full load is one of the most common causes of NFPA 110 test failures on natural-gas sets. (11.2.5)
12 Exhaust System
12.1 The exhaust system shall convey engine exhaust from the engine outlet to a discharge point that does not allow re-entry into the building, into the generator combustion air, or to areas where people congregate.
12.2 The exhaust system shall include a silencer sized for the project's sound attenuation requirement, a flexible exhaust connection between the engine and the silencer, condensate drains at low points, and aftertreatment components where required for emissions compliance.
12.3 Silencer Selection
Industrial (12 to 18 dB(A) insertion loss)
Residential (18 to 25 dB(A) insertion loss)
Critical / Hospital (25 to 35 dB(A) insertion loss)
Super-critical (above 35 dB(A) insertion loss)
12.3.1 Silencer grade shall be selected to achieve the project's sound limit at the nearest sensitive receptor.
12.3.2 The silencer's back-pressure shall not exceed the engine manufacturer's allowable back-pressure at full load.
NOTE Excess back-pressure reduces power and increases exhaust temperature, which can damage the engine. (12.3.3)
12.4 Exhaust Routing
● Schedule 40 carbon steel
○ Schedule 80 carbon steel
○ Stainless steel (corrosive environments or condensate)
○ Insulated where exposed within 8 ft of personnel routes
● Insulated entire run inside building
○ Not insulated (outdoor routing only)
12.4.1 The exhaust shall be routed in seamless steel pipe (Schedule 40 carbon steel as the default) with welded or flanged joints, supported clear of combustible construction with the clearances of NFPA 37 maintained, and insulated where exposed to personnel or combustible materials.
12.4.2 The discharge shall point away from building air intakes, with the separation from openings in the building required by NFPA 37.
12.4.3 A condensate trap and drain shall be provided at the low point of any exhaust run that can collect condensate, with discharge to a suitable waste connection.
12.4.4 Exhaust condensate is acidic and shall not be discharged onto building materials or to a storm drain.
12.5 Aftertreatment
12.5.1 Where the engine requires aftertreatment to meet EPA Tier 4 Final or another applicable standard, the diesel oxidation catalyst, diesel particulate filter, and/or SCR catalyst shall be furnished by the generator manufacturer as part of the exhaust system, with all sensors and the DEF (urea) tank and dosing system as applicable.
12.5.2 The aftertreatment shall be sized for the engine and located so that the exhaust temperature at its inlet remains above the catalyst's activation temperature during the project's typical operating cycle.
13 Enclosure and Sound Attenuation
Open set (indoor, mechanical room installation)
Weather-protective enclosure (basic outdoor housing)
Sound-attenuated enclosure (specify dB(A) target)
Walk-in sound-attenuated enclosure
6085
60657072758085
Default: 75 dB(A)
Per drawings
NOTE An open set is appropriate where the generator is installed inside a building room dedicated to it and the room provides weather protection, ventilation, and sound attenuation; a weather-protective enclosure is the minimum for outdoor installations, and sound-attenuated and walk-in enclosures incorporate acoustic lining, sound-attenuating intake and discharge openings, and exhaust silencer integration to meet a specified sound limit. (13.1)
13.2 The sound rating shall be specified at the manufacturer's standard measurement condition (typically 7 m from the enclosure under free-field conditions at the rated load).
13.3 The Engineer shall verify property line compliance separately.
NOTE Sound at the property line will generally be lower than the 7 m value because of distance attenuation, but reflections, intervening surfaces, and other sources may complicate the relationship. (13.4)
13.5 Enclosure Construction
● Galvanized steel with powder coat
○ Aluminum (coastal applications)
○ Stainless steel (severe corrosion)
13.5.1 The enclosure shall be fabricated from minimum 14 gauge steel with all seams welded or sealed, internal acoustic lining selected for moisture and fire resistance, hinged and lockable access doors on both sides for engine and alternator service, and a removable end panel or roof for major component removal.
13.5.2 The enclosure paint system shall be a polyester powder coat over corrosion-resistant primer with a minimum total dry film thickness of 3 mils; coastal and industrial environments shall receive an enhanced 5 mil minimum system.
13.6 Ventilation Openings
13.6.1 Intake and discharge openings shall be sized for the radiator air flow plus the combustion air, with motorized or gravity louvers that close when the engine is not running to keep wind-driven rain, snow, and animals out of the enclosure.
13.6.2 Louvers shall open before cranking begins so that they do not obstruct the radiator air path on starting.
14 Batteries and Charger
14.1 Starting Batteries
○ Flooded lead-acid
● Absorbed glass mat (AGM) sealed lead-acid
14.1.1 Cranking batteries shall be lead-acid (flooded or AGM), sized for the engine manufacturer's required cranking capacity at the design minimum temperature, conforming to EGSA 100B, mounted in a vibration-resistant rack on the set or in the enclosure.
14.1.2 NFPA 110 4.7.4 requires the battery to be capable of three complete cranking cycles at the design temperature without exceeding the manufacturer's limits.
NOTE AGM batteries are recommended over flooded for stationary generator service because they tolerate vibration better, do not require watering, do not vent acid gases in normal service, and are orientation-independent; flooded batteries remain acceptable where the lower first cost is preferred and the Owner has an established maintenance program. (14.1.3)
14.2 Battery Charger
5 A (small sets)
10 A (mid-range)
20 A (typical)
Per manufacturer (sized to battery)
14.2.1 A two-rate (float / equalize), temperature-compensated battery charger listed to UL 1236 shall be provided.
14.2.2 The charger shall maintain the battery at float voltage during normal standby and transition to bulk/absorption charging after an engine start without sulfating the battery on extended floats.
14.2.3 A battery charger malfunction contact shall be wired to the controller per NFPA 110.
14.2.4 The charger shall be powered from a dedicated branch circuit on the normal source, and shall be wired so that on loss of normal power the charger does not become a load on the generator.
14.2.5 The charger output shall include reverse polarity protection and short-circuit protection.
15 Vibration Isolation and Seismic
15.1 Vibration Isolation
○ Factory isolation only (outdoor pad-mount, no occupied space below)
● Factory isolation plus external spring isolators with seismic restraints
○ Factory isolation plus restrained spring isolators on inertia base
15.1.1 The generator set shall be mounted on factory-installed vibration isolators between the engine-alternator skid and the base or sub-base tank.
15.1.2 Where the set is installed inside an occupied building, additional spring isolators with seismic restraints shall be provided between the base and the housekeeping pad to limit structure-borne noise transmission.
NOTE A restrained spring isolator with an inertia base is appropriate where the set is installed above or adjacent to acoustically sensitive occupied spaces and the additional mass and isolation are needed to meet a noise criterion. (15.1.3)
15.2 Seismic Certification and Anchorage
Not required (no seismic risk)
ASCE 7 Seismic Design Category C - Importance Factor 1.0
ASCE 7 SDC D, E, or F - Importance Factor 1.0
ASCE 7 SDC D, E, or F - Importance Factor 1.5 (essential facility)
OSHPD pre-approval (California healthcare)
15.2.1 Where seismic certification is required, the complete generator set as assembled — including engine, alternator, controller, sub-base tank, and enclosure — shall be certified by shake-table testing per ICC ES AC156 or by analysis acceptable to the AHJ.
15.2.2 Anchorage to the housekeeping pad shall be by post-installed anchors sized for the certified base shear and overturning moment, installed per the certification documentation.
15.2.4 Where the project is an essential facility per ASCE 7 (Importance Factor 1.5), the set shall also be functional after the design seismic event; certification shall demonstrate operability and not only structural survival.
16 Testing
16.1 Factory Tests
16.1.1 The manufacturer shall perform the following production tests on every set prior to shipment per UL 2200 and ISO 8528-6:
- Full-load run at rated kW, voltage, and frequency
- Single-step rated load pickup
- Safety shutdown verification (overspeed, low oil pressure, high coolant temperature)
- Voltage regulation test through the load range
- Phase rotation and polarity verification
- Insulation resistance test on the alternator
- Visual and dimensional inspection
○ Not required beyond manufacturer's production tests
● Certified test report (unwitnessed)
○ Witnessed by Owner's representative
○ Witnessed and instrumented to ISO 8528-6 test protocol
16.1.2 Where witnessed testing is specified, the manufacturer shall provide at least two weeks notice of test readiness and submit the test procedure for review.
16.2 Field Acceptance Tests
16.2.1 The Contractor shall perform the NFPA 110 installation acceptance test on the completed installation, per NFPA 110 Chapter 7, including as a minimum:
- Cold start test demonstrating the NFPA 110 Type time from start signal to load acceptance
- A minimum of two hours of operation at not less than 30 percent of the rated load, with one of the loads being a step load representative of the building's largest single step
- Verification of all NFPA 110 alarms and shutdowns
- Verification of the remote annunciator function
- Transfer and re-transfer testing with the automatic transfer switch
- Verification of cool-down operation on return to normal source
- Functional test of the exerciser and any load bank interface
Building loads only (where they meet NFPA 110 30 percent threshold)
Load bank to NFPA 110 minimum (typically 30 percent)
Load bank to 100 percent of rated kW for two hours
Load bank to 100 percent and four-hour endurance run
NOTE A 100 percent rated load bank test is recommended at acceptance even when building loads alone would meet NFPA 110, because most building loads at the time of commissioning are well below the generator's rating, and wet stacking on a chronically under-loaded diesel is a common in-service problem. (16.2.2)
16.3 Commissioning Documentation
● Authority Having Jurisdiction witness required
○ Owner's commissioning agent witness
○ Engineer of Record witness
○ Test report certified by Contractor
16.3.1 The Contractor shall provide a written, signed NFPA 110 installation acceptance test record.
16.3.2 The record shall include the date of test, the technicians performing the test, the instruments used, the measured start time, the load profile, observed alarms, corrective actions if any, and the AHJ witness signature where the AHJ elects to witness.
16.4 Infrared Scanning
● Initial scan within 90 days plus follow-up at 11 months
○ Initial scan within 90 days only
○ Not required
16.4.1 An infrared thermographic scan of all power terminations and bus connections shall be performed under full load within 90 days of energization, with a follow-up scan at 11 months to capture any connections that loosen during initial thermal cycling.
16.4.2 Connections showing more than 10 deg C rise above ambient or 5 deg C rise above similar adjacent connections shall be corrected.
17 Installation
17.1 Concrete Housekeeping Pad
17.1.1 The generator set shall be set on a reinforced concrete housekeeping pad sized to extend at least 6 in. beyond the set's footprint on all sides, with a minimum thickness sufficient to accept the anchor embedment depth required by the seismic anchorage design, and an upper surface elevation of at least 4 in. above the surrounding floor or grade.
17.1.2 Pad construction shall be coordinated with Concrete Pads and with the structural drawings. 17.1.3 Conduit penetrations, fuel line penetrations, and grounding electrode connection points shall be cast or sleeved into the pad before concrete placement.
NOTE Drilling and chipping the housekeeping pad after the fact for cable entries is poor practice and weakens the anchorage. (17.1.4)
17.2 Clearances
Per manufacturer's recommendation (typically 3 ft on service sides)
Per NFPA 70 110.26 (electrical working space) - minimum
Walk-around access on all four sides
17.2.1 Working clearances around the generator set and its controller, transfer switch, and main line breaker shall comply with NFPA 70 Article 110.26.
17.2.2 The Contractor shall confirm that the planned location accommodates the larger of the NFPA 70 working clearances and the NFPA 37 clearances between the engine and combustible construction, between the exhaust pipe and combustibles, and around the enclosure for service access.
17.3 Conduit, Cable, and Grounding
○ Switched neutral at ATS - generator is a separately derived system
● Solid (non-switched) neutral at ATS - generator is not separately derived
17.3.1 Power and control conduit entries shall be located per the shop drawings, with watertight fittings on outdoor enclosures and bushings or hubs as required for the cable system.
17.3.3 The generator frame and the alternator neutral (where applicable) shall be grounded per NEC Article 250 and per Grounding And Bonding. 17.3.4 The Contractor shall confirm the transfer switch arrangement before bonding the neutral, and shall coordinate with the transfer switch submittal under Automatic Transfer Switches. 17.3.5 A generator that is a separately derived system shall have its neutral bonded to ground at the set and a grounding electrode connection per NEC 250.30.
17.3.6 A generator with a solid (non-switched) neutral through the ATS shall not have its neutral bonded to ground at the set, because the service main bonding jumper already provides the system bond and a second bond creates objectionable parallel neutral current.
NOTE Whether the generator is a separately derived system depends on the transfer switch's neutral treatment. (17.3.7)
17.4 Fuel and Exhaust
17.4.1 Fuel piping, fuel tank vents, and fuel fill connections shall be installed per NFPA 30 (diesel) or NFPA 54 / 58 (gas).
17.4.2 Exhaust piping shall be supported and routed per NFPA 37 with the required clearances from combustibles, and discharge shall comply with the air permit and with NFPA 37 separation from building openings.
18 Identification and Labeling
☑ Equipment designation matched to one-line diagram
☐ EPS supply identification per NEC 700.10(A) (emergency systems)
☐ Available fault current label per NEC 110.24
☐ Arc flash warning label per NFPA 70E and IEEE 1584
☐ NFPA 110 Level and Type identification at the set
☐ Emergency power source identification at served panelboards
18.1 Each emergency system component, including the generator, shall be marked at its enclosure as part of an emergency system per NEC 700.10(A).
18.2 The available fault current at the generator main breaker and at the load side of the transfer switch shall be calculated, labeled, and dated per NEC 110.24.
19 Delivery, Storage, and Handling
19.1 The generator set shall be shipped from the factory with the engine pre-filled with the manufacturer's recommended lubricant, the cooling system filled or drained-and-tagged per the storage plan, batteries shipped dry or wet per the manufacturer's recommendation, and all shipping braces and weather seals in place.
19.2 Sets stored on site for more than 30 days before energization shall be stored under cover, with the jacket water heater and battery charger connected to a temporary source if available, and shall be turned over periodically per the manufacturer's storage instructions.
19.3 The Contractor shall verify clearances along the entire delivery path — gates, doors, ramps, elevators, structural floor capacity — before the set arrives.
NOTE Large sets are routinely re-routed at the last minute because someone discovered a doorway that the set will not pass through; this is avoidable with a pre-delivery survey. (19.4)
20 Warranty
1 year from substantial completion or first start, whichever is earlier
2 years / 1,000 hours, whichever occurs first
5 years / 1,500 hours extended (premium)
Custom (specify in submittal)
20.1 The warranty shall cover defects in materials and workmanship under normal standby use.
20.2 The warranty period shall include the manufacturer's commitment to provide a field-service technician on site within four hours of notification of a critical failure, 24 hours per day, for the duration of the warranty.
NOTE Owners commonly extend the warranty to five years on critical-mission installations. (20.3)
21 Spare Parts and Maintenance Materials
☑ One set of engine filters (oil, fuel, air, coolant)
☐ One set of belts and hoses
☐ Spare set of alternator brushes (where applicable)
☐ Spare battery (matched to installed set)
☐ Spare control fuses and indicating lamps
☐ Touch-up paint matching enclosure finish
21.1 Spare parts shall be stored on site in a labeled cabinet in the generator room or electrical room.
21.2 The O&M manual shall list the part numbers, supplier, and reorder lead times so that the Owner can replenish without relying on the original Contractor.
21.3 Owner Training
4 hours (minimum)
8 hours (split between operations and maintenance)
16 hours (operations, maintenance, and troubleshooting)
21.3.1 The generator manufacturer's authorized service representative shall provide a minimum of four hours of on-site training to the Owner's operating personnel.
21.3.2 Training shall cover normal operation, the controller interface, the exerciser configuration, the alarm and shutdown response procedure, NFPA 110 testing and recordkeeping, and routine maintenance intervals.