How to use this glossary
These concise definitions explain common terms, not a specific design. Manufacturer values and code requirements can be model- and location-specific. Read the exact manual and ask a qualified local professional before making equipment or installation decisions.
Electrical and transfer terms
- Automatic transfer switch (ATS)
- Equipment that changes the connected load between utility and generator sources as part of a compatible system. The exact sensing, timing, neutral, service, and load-control arrangement depends on the switch and generator models.
- Manual transfer switch
- A switch that requires a person to change between utility and generator power. Circuit coverage, rating, and operating steps are specific to the installed equipment.
- Panel interlock
- A mechanical accessory intended for a compatible electrical panel and breaker arrangement. It is not universal; the exact panel/accessory compatibility, installation, and local approval must be checked.
- Backfeed
- Electrical energy flowing toward a source or conductors that are not intended to be energized by the generator. CPSC warns not to connect a generator to house wiring by plugging it into a wall outlet; use properly installed transfer equipment.
- Load management / load shedding
- A control strategy that may delay, sequence, or disconnect selected loads when system conditions require it. Which loads can be managed and how they behave depend on the exact equipment and configuration.
- Service-entrance-rated switch
- Transfer equipment identified by its manufacturer for a particular service-entrance application. The rating does not by itself establish the switch’s compatibility with a specific panel or complete installation.
Ratings and performance terms
- Kilowatt (kW)
- A unit of real electrical power. A generator’s kW rating is only meaningful alongside the model, fuel, phase, voltage, and rating conditions.
- Kilovolt-ampere (kVA)
- A unit of apparent electrical power. The relationship to real power depends on power factor; do not assume a universal conversion when comparing equipment.
- Power factor
- The ratio of real power (kW) to apparent power (kVA) for an AC load under the stated conditions. Use the value or rating applicable to the specific generator or load.
- Standby rating
- A manufacturer’s stated output rating for standby/emergency use under stated conditions. Definitions and overload capability can differ; for example, the cited Generac sheet says its listed standby rating has no overload capability. Check the exact model documentation.
- Locked-rotor amps (LRA)
- A motor’s nameplate or manufacturer value associated with starting current. It may help describe motor-start demand, but LRA alone is not a complete generator-sizing calculation.
- Total harmonic distortion (THD)
- A measure of harmonic content in an electrical waveform relative to its fundamental component, commonly expressed as a percentage. Test load and method matter; do not compare ratings without their stated conditions.
- dB(A)
- A sound level expressed using A-weighting. Distance, microphone direction, operating mode, load, surroundings, and the manufacturer’s test method all affect whether two reported values can be compared.
- Exercise mode
- A scheduled generator test or exercise operation. Timing, duration, speed, loading, and controller behavior vary by model and settings; use the current owner manual.
Fuel and site terms
- Fuel-specific output
- The rated power a particular model publishes for a stated fuel and configuration. A natural-gas rating and an LP rating may differ; do not substitute one for the other.
- Dual-fuel standby generator
- A standby model designed to operate on either of two specified fuels, commonly natural gas or LP. The chosen fuel, field configuration, output, fuel use, and supply requirements must be confirmed for that model.
- Fuel-consumption test point
- A manufacturer-published fuel-use value at a stated load and test condition. It is not automatically a household average or a fuel-bill prediction.
- Fuel inlet pressure and flow
- The pressure and volume available at the generator connection while operating. The exact model’s installation manual specifies requirements; a qualified installer or fuel provider must verify the supply under the proposed load.
- Site derating
- A reduction in available output that may apply under environmental or installation conditions identified by the manufacturer. The conditions and calculation are model-specific; there is no universal percentage for every generator.
Reliability and code terms
- SAIDI
- System Average Interruption Duration Index: EIA describes it as the total duration of non-momentary interruptions experienced by an average customer in a year. It is a utility reliability measure, not a prediction for one home.
- SAIFI
- System Average Interruption Frequency Index: EIA describes it as the number of interruptions in a year. Check the data notes and event-inclusion rules when comparing values.
- Authority Having Jurisdiction (AHJ)
- The authority responsible for applying or enforcing relevant requirements in a particular location. The responsible office and adopted rules can vary by jurisdiction.
- National Electrical Code (NEC / NFPA 70)
- A model electrical code published by NFPA. The edition adopted locally and any local amendments determine what applies; installation design and approval are not established by this glossary.
Continue with a specific question
For actual appliance input, use the manufacturer-published generic wattage reference only as a starting point, then obtain exact nameplate data. For model ratings, see the brand data pages; for safe operation, read the safety guide.