GENERAC 7128 GP3500iO Open Frame Inverter 50 ST/CSA

The GP3500iO (model 7128) is rated 3000 running watts with 3500 surge watts, all at 120 volts. Generac's PowerRush technology bumps electrical current on demand above rated output when starting electric motors, which is what gets a compressor, pump or power tool through its inrush. Size the running load at 3000 W and leave the surge headroom for the motor start.

No. It's 120 volts only. The panel carries one 120V 20A 5-20R duplex, one 120V 30A L5-30R twist lock, and two USB ports. That 30A twist lock will feed a 120V-only transfer switch or an RV-style adapter, but anything needing 240V single phase, like a deep well pump or a whole-panel switch, needs a different generator.

It weighs 74.3 lbs and measures 19.7 in long by 16.5 in wide by 16.4 in high, so it's a two-hand lift for most people and an easy two-person load. No wheel kit is included, so if it's moving around a site all day plan on a cart or a separate kit. Generac states it's 25 percent lighter than the GP3300.

Yes, the 7128 is CARB compliant, so it can be sold and operated in California. It's also CSA Certified and UL Listed, which covers Canadian jobs and facilities that require a listed unit.

It's an inverter alternator, not a conventional one, and Generac markets the output as TruePower clean power for sensitive electronics. That's the reason to pick this over an open-frame conventional unit for computers, monitoring gear, POS terminals or battery chargers on a site.

About 4.5 hours per tank at half load, from a 2.37 gallon gasoline tank. There's a fuel gauge on the unit so crews can see what's left without opening the cap. For an overnight run you're refueling at least once.

The GP3500iO is the open-frame style: a steel frame around the engine rather than a sealed plastic shell. That keeps weight and size down (74.3 lbs) and makes the engine, oil fill and plugs easy to reach for service, which matters on a rental or fleet unit. Generac rates it 50 percent quieter than the GP3300, but a fully enclosed inverter is still the quieter choice for a campground or a noise-restricted residential street. For general contractor use, open frame is the practical pick.

Pull start only. Starting, running and stopping all run through Generac's single PowerDial, so there's no separate fuel valve and choke sequence to learn, but there is no electric start key, no battery and no Bluetooth or phone app on this model.

No cord is included. You supply the extension cords, and for the 30A twist lock outlet you'll need an L5-30P cord or adapter to get to standard 5-15/5-20 receptacles. The 5-20R duplex takes a normal 120V cord as is.

A 212 cc gasoline engine with low oil shutdown, which kills the engine before it runs dry. That's the feature that saves a rental or loaner unit from an operator who never checks the dipstick. Still check oil at every fill.