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Generator Glossary

Glossary of common terminology

In order to help you better understand some of the technicalities associated with purchasing a generator, below is a list of common terms and definitions used in the generator industry. Please feel free to call your Leete Generators Power Specialist with any questions that may arise.

Air-Cooled.  Used to describe a genset that uses air to cool the engine, alternator, and other components.  In contrast to water-cooled, air-cooled gensets are typically high-speed and cost significantly less, but are less dependable and have a shorter expected lifespan.

Alternator.  The component on a genset that produces electrical output when a mechanical force is applied, usually via an engine.  Alternators can be either stand-alone or incorporated as an integral component of a genset.  Often times, the alternator is less accurately referred to as a “generator.”

ATS.  Short for “automatic transfer switch.”  ATS’s operate automatically in response to power outages and or brownouts, starting and stopping standby gensets as required without the need for human intervention.

AVR.  Short for “automatic voltage regulator.”  AVR’s are electronic devices that control the voltage output of a generator to exacting accuracy.  In contrast to capacitive regulators, AVR’s are required in applications where entertainment systems, computers, healthcare equipment, microwave ovens, televisions, UPS’s and other sensitive electronic devices are to be powered by the generator.  See “Clean Power.”

Back-Feed.  This term is used to describe the introduction of external electrical power into a municipality’s electrical system and is usually caused by failure to comply with NEC regulations.  Note: genets should never be plugged directly into an electrical receptacle.  This is an extremely serious matter, as life-threatening injury and or death may occur to unsuspecting line workers.  For this reason, it is imperative that only properly licensed electrical contractors experienced with generators perform installations.

Continuous Rating.  Used in contrast to “surge rating,” this term describes the maximum output at which a genset or alternator is rated to run for an extended time period.  Please note: the definition of an “extended time period” is determined solely by the manufacturer and will vary for each genset and application.

Clean Power.  This term describes an electrical power supply that displays tightly regulated and accurate voltage and frequency characteristics.  Clean power is required to properly operate sensitive microprocessor-controlled equipment such as entertainment systems, computers, healthcare equipment, microwave ovens, televisions, UPS’s, and etceteras.

Control Panel.  This genset component controls the engine operation and may also display system performance information and parameters via various gauges, meters, LCD’s, LED’s, and CRT’s.

Electronic Governor.  See “isochronous governor.”

Enclosure.  Also called a “housing.”  An enclosure is an assembly typically attached to the skid that protects gensets from exposure to weather, rodents, and other harmful forces.  Virtually all enclosures are NEMA 3R-rated.  Further, most enclosures are equipped with locks to prevent tampering by unauthorized personnel and can also be sound attenuated to reduce the inherent noise level.

Engine.  This genset component is used to rotate the alternator.  Engines are controlled by the governor and are available in diesel, gasoline, liquid propane, liquid propane vapor, and natural gas fuel configurations.  Unlike automobiles, genset engines operate a constant rpm, while the horsepower is manipulated to meet system requirements.

Frequency.  This is a characteristic of electrical power and is controlled by the governor.  Measured in cycles per second (Hertz), the US standard is 60 Hz.

Generator.  Used interchangeably with “generator set” or “genset.”  Frequently, this term is less accurately used to describe the “alternator” component alone.

Generator set.  Also referred to as “genset.”  A generator set is a self-contained apparatus that houses all the components necessary to produce an electrical output.  In most cases, this includes four major components and their associated sub-systems including the engine, alternator, control panel, and skid.  Please note that the skid is often equipped with an enclosure.

Genset.  Short for “generator set.”

Governor.  A device that controls engine speed, thereby controlling the output frequency.  Governors can be either mechanically or electronically actuated.  See “Isochronous Governor.”

High-speed.  Used to describe a genset that runs at 3,600 rpm (60 Hz applications).  In contrast to low-speed, high-speed gensets are typically air-cooled and cost significantly less than their low-speed alternatives, but produce more noise and have a shorter expected lifespan.

Home Standby.  In contrast to “industrial” or “portable,” this term is used to describe equipment or applications that relate to use in homes, small business, or commercial applications.  See “Standby” for further detail.

Housing.  Please see “enclosure.”

Industrial.  This term is used to describe equipment or applications that relate to heavy-duty, strenuous, large, and or primary power applications.

Isochronous Governor.  Also called an “electronic governor.”  This device maintains the engine speed to exacting tolerances, thus tightly controlling the output frequency measured in hertz.  In the United States the frequency is at 60hz, in other parts of the world it’s measured at 50hz.  Electronic governors are often required in applications where sensitive microprocessor-controlled equipment, such as entertainment systems, computers, healthcare equipment, microwave ovens, televisions, and UPS’s.  See “Clean Power.”

KW.  Short for “kilowatt.”  This is a measurement of wattage reported in thousands of watts.  For instance, 8500 watts is the same as 8.5 kW and is used primarily to describe genset output capacity or load capacity.

Load Capacity.  The amount of electrical power a circuit, wire, and or device is designed to produce and or carry.  Load capacity usually has two components – surge, or temporary, and continuous.

Loaded.  Also referred to as “live,” this term is used to describe situations where electrical power is flowing through a circuit, wire, and or device.

Low-speed.  Used to describe a genset that runs at 1,800 rpm or lower (60 Hz applications).  In contrast to high-speed, low-speed gensets are typically water-cooled, last longer, run quieter, and are less costly to operate.

Manual Transfer Switch.  This is a transfer switch that is manually operated, usually by actuating a spring-loaded lever.  In contrast to a “safety switch,” true transfer switches are designed for operation while loaded.

Motor Starting Capacity.  This term describes the largest motor a given alternator or genset is able to start and is usually reported in horsepower and winding code.  Please note: motor starting capacity is often mistaken with “surge capacity.”

Multi-Fuel.  This term is used to describe gensets that are equipped to run on more than one fuel source.  For portable gensets, the fuel options are gasoline with either liquid propane vapor or natural gas.  Switchover from one fuel source to another is accomplished via manually actuated levers located on the carburetion system.  For home standby and industrial gensets, the fuel options are natural gas and liquid propane vapor only.  In such applications, switchover occurs automatically when the fuel line pressure of the primary fuel source falls below a preset threshold.  There are a few large generators that operate by mixing natural gas and diesel fuels, but they are rare.

NEC.  Short for “National Electrical Code.”  This is the set of rules and regulations that dictate how electrical installations are to be performed, including generators, transfer switches, and UPS’s.<

NEMA.  Short for “National Electrical Manufacturer’s Association.”  This organization sets the standards to which electrical equipment is manufactured.

NEMA 1.  This indicator is used to denote electrical equipment that has been designed for use in dry, indoor environments only

NEMA 3R.  This indicator is used to denote electrical equipment that has been designed for use in outdoor environments subject to rain and snow.

NFPA.  Short for “National Fire Protection Agency.”  The NFPA sets the standards to which generators must perform in certain critical applications such as in healthcare facilities, fire pumps, and police stations.

Noise Level.  This is the amount of noise a genset produces and is generally reported in dbA (decibels).  Typically, the average of eight measurements taken from equally spaced locations around the perimeter of the genset at a distance of seven meters (twenty-three feet) is provided.

Portable Genset.  These are small, low-cost, air-cooled gensets designed primarily for construction worksite applications.  Portable gensets are also sometimes used for non-critical emergency applications where functionality and convenience are sacrificed in order to keep costs to a bare minimum.

Primary Power.  Also referred to as “prime power.”  This term is used to describe a genset and or application that is designed, rated, and approved for continuous operation, twenty-four hours a day, seven days a week where no other power supply is available.  Virtually all primary power gensets are water-cooled and low-speed, and are nearly always diesel fueled.

Residential Standby.  See “home standby.”

Safety Switch.  This is a low-cost switch, usually of wiper-and-blade configuration, that is sometimes substituted for a true transfer switch.  Please note using a safety switch for standby genset installations is a substandard practice, as is it NOT designed for use in loaded applications.

Skid.  Sometimes referred to as the “base.”  The skid is the structure on which genset components are mounted.  Gensets may be configured as “open” (without an enclosure), with a weather protective housing, or with a sound-attenuated weather housing.

Sound Attenuated.  This is an enclosure that has been engineered to reduce noise level.  They may be an integral part of the genset or an aftermarket addition and are available in a myriad of sizes and performance levels.

Standby.  This term is used to describe equipment or an application that is non-continuous in nature such as emergencies and or when the municipal power supply has failed.  Standby can be further divided into sub-classes including “residential” and “commercial.”  Further, more specific definitions are often implied, although such definitions vary widely by model and manufacturer.

Standby Rating.  This term describes the output a generator or genset is rated to produce for an indefinite, but temporary time period, usually of less than eight hours duration.  It is used in contrast to “primary power.”

Surge Rating.  This term describes the maximum output a generator can produce for an extremely short time interval; usually ten seconds or less.  It is commonly used to imply “motor starting capacity,” although this is an incorrect usage and may be dangerously misleading.

Transfer Switch.  Transfer switches are installed between an alternator or genset and a municipal power supply or other power source to prevent back-feed or otherwise separate the auxiliary power supply from the main system.  Many types of transfer switches are available with numerous options.  See “automatic transfer switch” and “manual transfer switch” for additional detail.

Tri-fuel.  This is a term used by some manufacturers to describe a genset that is equipped to run on three different fuel types.  See “Multi-Fuel” for additional detail.

UL Listed.  Various UL listings are applicable to alternators, gensets, transfer switches, UPS’s, and other electrical equipment.  To obtain a UL listing, equipment must be designed and manufactured to specific requirements intended to ensure a product that is safe for use in the intended application.  Please note that, contrary to popular belief, a UL listing does not imply anything akin to a guarantee, nor does it indicate that the specific piece of equipment has been tested in anyway, whatsoever.

UPS.  Short for “uninterruptible power supply.”  Essentially, UPS’s are backup batteries with built-in control electronics that circumvent power disruptions, thus preventing the loss of critical information and or interruption of equipment usage.  UPS’s are commonly used for computers, healthcare equipment, and other electronically controlled apparatuses.

Voltage.  Voltage is a characteristic of electrical power and is controlled by the AVR or other voltage-regulating device, such as capacitors.  Measured in volts, the US standard is 120/240 for residences on single phase, although in actuality it may be as low as 105/210 depending upon a number of factors controlled by the municipal utility.  In an industrial environment, 3-phase voltages are used.  They are 120/208, 120/240, or 277/480.

Water-cooled.  Also referred to as “liquid-cooled,” this term is used to describe gensets that most often employ a closed-loop recirculation system with a radiator and blower to cool the engine.  In contrast to air-cooled, water-cooled gensets are typically more robust and last significantly longer.  With very few exceptions, water-cooled gensets are also low-speed.<

Winding Code.  This is a letter designation used to reference how a motor was manufactured.  Knowing the winding code and horsepower of a motor is essential to determine the proper size and configuration of alternators and or gensets intended for motor starting applications.  See “motor starting capacity.”