Sharing our Guidance

Backup Generators

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04/13/23 2

What Is A Generator?

• A generator is a machine that converts mechanical

energy into electrical energy.

• Serve as a power source in the event of utility power

failure

• Sources of mechanical energy can include:

• Steam engine

• Waterwheel

• Hand crank

• Compressed air

• Internal combustion engine

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Generator Fuel TypesSUMMARY OF FUEL FACTORS

FACTOR GASOLINE DIESEL & MIXES NATURAL GAS VAPOR PROPANE LIQUID PROPANE

ENGINE COSTEXCELLENT

(MANY LOW COST GENSETS ON THE MARKET)

EXCELLENT (HIGH COST IN SMALL SIZES)

EXCELLENT (LOW COST IN SMALL SIZES)

EXCELLENT (LOW COST IN SMALL SIZES)

EXCELLENT (LOW COST IN SMALL SIZES)

FUEL SYSTEM INSTALLATION & STORAGE COST

VARIES (LOW COST IN SMALL SIZES)

VARIES (LOW COST IN SMALL SIZES)

EXCELLENT (IF GAS SERVICE ALREADY

AVAILABLE AT SITE)

EXCELLENT (IF ADEQUATELY SIZED TANK

ALREADY AT SITE)

EXCELLENT (IF ADEQUATELY SIZED TANK

ALREADY AT SITE)

FIRE PERSONNEL SAFETYPOOR (HIGHLY

FLAMMABLE, POISONOUS VAPORS)

EXCELLENT (HIGH FLASH POINT)

MEDIUM (RARE LEAK RISK)

MEDIUM (RARE LEAK OR TANK EXPLOSION

RISK)

MEDIUM (RARE LEAK OR TANK EXPLOSION

RISK)

ENVIRONMENTAL IMPACTSPOOR

(SPILL RISK, EXHAUST NOT CLEAN)

POOR (SPILL RISK, EXHAUST NOT CLEAN)

EXCELLENT (CLEAN BURNING)

EXCELLENT (CLEAN BURNING)

EXCELLENT (CLEAN BURNING)

FUEL AVAILABILITY MEDIUM (EASY TO PURCHASE)

MEDIUM (MUST BE DELIVERED & STORED)

EXCELLENT (STORAGE NOT REQUIRED, SUPPLY

RARELY LOST)

MEDIUM (MUST BE DELIVERED & STORED)

MEDIUM (MUST BE DELIVERED & STORED)

COLD STARTING & OPERATION POOR (FORMS GUM DEPOSITS)

MEDIUM (HARD STARTING AT COLD

TEMPERATURES)EXCELLENT

MEDIUM (TANK MUST BE LARGE &

FULL)

EXCELLENT (NO VAPORIZATION ISSUE)

ENGINE LIFE/WEAR POOR/MEDIUM (DEPENDS ON ENGINE TYPE) EXCELLENT MEDIUM MEDIUM MEDIUM

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Engine Generator Requirements

• Required to have enough fuel to run generator at full load for 2

hours minimum

• Generators generally consume 7 gallons/hour for every 100kW

of generator capacity

• Some critical facilities store up to 72 hours of fuel

• Fuel can be stored in belly tanks under the generator or separate

tanks

• Storage limited to 660 gallons inside a structure or on the roof

(NFPA 110 7.9.5)

• Subject to strict emission standards (Tier 1, 2, 3, 4)

• NEC Article 445 – Generator Installation/Requirements

• NEC Articles 700, 701, and 702 – Backup Load Types

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Backup Load Types

1. Emergency

• Legally required and classified as emergency by code

• Automatically supply light, power, or both essential for safety of human life

• Egress lighting, fire detection/protection, elevators, public safety

communications, etc.

• Power must be available within 10 seconds

2. Legally Required Standby

• Legally required by code

• Provide power to systems that may create hazards or hamper firefighting

operations if off

• Communications, ventilation, smoke removal systems, lighting, industrial

processes, etc.

• Power must be available within 60 seconds

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Generator Power Source Categories

3. Optional Standby

• Loads that do not affect life safety but would result in

unacceptable financial or operational losses to a facility

• Data processing, communication systems, refrigeration,

HVAC loads, critical processes, etc.

• Power must be available within 60 seconds

4. Mission Critical

• Designated by local, state, or federal government

• Loads that are necessary for public safety, national

security, business continuity

• Data centers, semiconductor manufacturing, etc.

• Power must be available within 60 seconds

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Backup System One Line Diagram

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Loading & Generator Sizing

• Emergency and required standby system loads must be applied

without demand factors

• Full load must be applied to the generator at all times

• Must include starting currents of motors on the system

• Use of a generator sizing program is recommended:

• Inductive loads can present concerns with inrush

• Harmonics

• Voltage regulation

• Load shedding or sequencing must be implemented when

including emergency and non-emergency loads on the same

generator

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Generators vs. Batteries

GENERATOR BATTERIES

START UP TIME 10-60 SECONDS MILLISECONDS

NOISE NOISY QUIET

FUEL RESERVE SUPPLY NONE NEEDED

RUN-TIME AS LONG AS FUEL IS AVAILABLE

UNTIL BATTERIES ARE DISCHARGED

UPFRONT COST MORE EXPENSIVE LESS EXPENSIVE

MAINTENANCE HIGH MAINTENANCE LOW MAINTENANCE

LIFE SPAN LONG LIFE SPAN SHORT LIFE SPAN

BACK UP TYPE LONG TERM SHORT TERM

CONCLUSION

THANK YOU.