Generator glossary

Short, direct answers to the terms that come up when choosing backup power.

50-amp inlet (14-50 / CS6365): Large portable generators above the 7,200 W ceiling of a 30 A connection use a 50-amp, 120/240 V connector — either a straight-blade 14-50R (the “RV/range” outlet) or a CS6365 twist-lock — carrying up to 12,000 watts into a 50 A generator inlet.
Automatic transfer switch (ATS): An automatic transfer switch monitors utility power and switches the house to generator power without human action — it signals a standby generator to start, transfers the load once output is stable, and transfers back when the utility returns.
CO safety shutoff: A CO safety shutoff is a built-in carbon monoxide sensor that stops the generator’s engine automatically when CO accumulates around the unit — sold under names like CO-MINDER, CO Shield, CO Guard, and CO Sense. It is a backstop, not a license to run a generator near the house.
Dual fuel: A dual-fuel generator runs on either gasoline or propane, switched by a selector and a regulator. Propane stores indefinitely and stays available when storms close gas stations, at the cost of roughly 10% less output than the gasoline rating.
EPA / CARB compliance: All new generators sold in the US must meet EPA emissions standards; CARB compliance is California’s stricter certification, required to sell a generator in California. Neither is a performance rating — they certify exhaust and evaporative emissions.
Floating vs bonded neutral: A bonded-neutral generator connects its neutral to the frame (its own ground); a floating-neutral generator leaves them separate, expecting the building’s panel to provide the bond. The wrong pairing with a transfer switch can trip GFCIs or defeat ground-fault protection.
Generator cord gauge: Cord gauge (AWG) sets how much current a generator cord can carry safely and how much voltage it loses over distance: 10 AWG for 30 A circuits, 6 AWG for 50 A, and thicker (lower-number) wire the longer the run.
Interlock kit: An interlock kit is a sliding metal plate on the breaker panel that makes it mechanically impossible to close the generator backfeed breaker while the main breaker is on. It is the low-cost alternative to a transfer switch for connecting a portable generator.
Inverter generator: An inverter generator converts its alternator’s raw output to DC and re-synthesizes clean AC electronically, producing low-distortion power at any engine speed. The result is quieter operation, better fuel economy at partial load, and output safe for sensitive electronics.
L14-30R outlet: The L14-30R is the standard 30-amp, 120/240-volt twist-lock receptacle found on most mid-size portable generators. It carries up to 7,200 watts through a single cord and is the usual connection point for a transfer switch or interlock.
Load shedding: Load shedding is automatically dropping lower-priority circuits when generator demand approaches capacity — letting a smaller standby generator protect a whole panel by making sure the air conditioner and dryer never run at the same time.
Parallel kit: A parallel kit is a cable set that links two inverter generators so their outputs combine into one circuit — two 2,200 W units become roughly 4,000 W of capacity. Only inverter generators designed for paralleling (usually matched models) support it.
Propane BTU content: Propane carries about 91,500 BTU per gallon — the number that converts a generator’s gallons-per-hour appetite into runtime from a given tank. A 20 lb grill cylinder holds about 4.6 gallons (~420,000 BTU); gasoline carries about 114,000 BTU per gallon.
Run time rating (at 25% / 50% load): Generator runtimes are quoted at a fraction of rated load — usually 25% or 50% — on a full tank. A “12 hours at 50%” unit running near full load may manage only 5–6 hours, so match the load fraction to how you will actually use it.
Starting watts vs running watts: Running watts is the power a generator sustains continuously; starting watts is the extra surge it can supply for a few seconds while a motor spins up. Size a generator so running loads fit the running rating and the single largest motor start fits within the starting rating.
Total harmonic distortion (THD): THD measures how far a generator’s AC output deviates from a pure sine wave, as a percentage. Under 5% THD is generally considered safe for sensitive electronics; conventional open-frame generators can exceed 15–25%, while inverter generators typically stay under 3%.
Transfer switch: A transfer switch is a device that connects a generator to a home’s circuits while physically disconnecting them from the utility line, so generator power can never backfeed the grid. It is the code-required way to power hardwired circuits from a generator.
Tri-fuel: A tri-fuel generator runs on gasoline, propane, or natural gas. The natural-gas option lets a portable unit draw unlimited fuel from the home’s gas meter — with the lowest output of the three fuels, typically about 20% below the gasoline rating.