Chapter 25: Generator Installation

OKC weather is, frankly, a generator-justifying climate. Ice storms can knock out power for days. Tornado season can produce localized outages. Summer thunderstorms regularly cause neighborhood-level interruptions. A generator can mean the difference between sweating through a powerless August night and being comfortable.

This chapter covers the two main residential generator approaches: portable generators with interlock kits, and standby generators with automatic transfer switches. Both approaches require equipment-specific planning. Have a licensed electrician install and verify any inlet, transfer equipment, interlock, or panel connection; homeowners operate an installed system only under its manufacturer and installer instructions.

Estimated time: 4–8 hours for portable generator setup. Multiple days for standby. Cost: $300–2000 for portable solutions. $4000–15000+ for standby. Permit required: yes for both approaches.

Two Approaches: Portable vs Standby

Portable generator:

• Wheeled unit, gasoline or dual-fuel (gas/propane)
• 3,000–12,000 watts typical
• $400–2000
• Stored in garage or shed
• Manually started and connected when power goes out
• Connects via an "interlock kit" that prevents back-feeding the utility lines

Standby generator:

• Permanently installed unit, often natural gas or propane
• 8,000–26,000 watts typical
• $4,000–15,000+ installed
• Runs automatically when utility power fails
• Connects via an "automatic transfer switch" (ATS)

The choice depends on:

• Budget
• How critical reliable power is for you
• How long you can tolerate manual startup time
• Whether you have natural gas or propane available

For most homeowners, a 7,500W portable generator with an interlock kit is the practical choice. It costs about $1,000–1,500 total and handles essentials (refrigerator, lights, some HVAC, charging devices) well.

Portable Generator with Interlock Kit

This is an overview of a professionally installed system. The general concept:

• A "generator inlet" (a special outdoor outlet) is installed on the side of the house.
• An interlock kit is added to the main panel. The kit prevents the main breaker and the generator breaker from being on simultaneously.
• During an outage: turn off the main breaker, plug the generator into the inlet, start the generator, turn on the generator breaker. Power flows from the generator through the panel to selected circuits.

MATERIALS

• Generator (typically 5,000–7,500W is the sweet spot for residential)
• Generator inlet box (NEMA L14-30 for 30A, L14-50 for 50A, mounted outside)
• Interlock kit specific to your panel brand and model
• 6/3 or 10/3 NM-B cable from inlet to panel (depending on amperage)
• Generator-rated breaker (30A or 50A double-pole, depending on inlet)
• Generator power cord (matches the inlet plug type)
• Permit

Total: $700–1500 in materials beyond the generator itself.

INSTALLATION

Have a licensed electrician select and install equipment compatible with the panel and generator, determine the grounding and neutral arrangement, complete the required permits and inspection, and verify transfer operation. Keep panel covers in place. Do not install an inlet, interlock, or backfeed breaker by following a generic guide.

OPERATING PROCEDURE DURING AN OUTAGE

Follow the exact generator, transfer-equipment, and installer operating instructions for your installed system. Do not use a generic switching sequence, defeat an interlock, or connect a generator through an ordinary receptacle.

For portable generators, operate outdoors at least 20 feet from homes and buildings, with exhaust directed away from windows, doors, and vents. Never operate inside a home, garage, porch, carport, or enclosed space. Follow manufacturer instructions for wet weather and stop for damaged cords or equipment. See CPSC's carbon-monoxide and generator guidance.

Generator Sizing for Portable Use

Sizing is about realistic load expectations, not theoretical maximum.

Common loads (peak watts; sometimes called "starting watts"):

• LED lights: 5–15W each
• Refrigerator: 600–800W running, 1500–2500W startup
• Furnace fan (gas heat): 600–800W
• Small window AC: 1000–1500W
• Microwave: 1000–1500W
• Coffee maker: 1500W
• Phone/laptop chargers: 50–100W each
• TV: 200–300W
• Sump pump: 800–1200W running, 2000–3000W startup

A 5,500W generator handles "the essentials" for most homes (lights, refrigerator, furnace fan, some chargers, a TV, microwave at occasional intervals). A 7,500W generator adds capacity for some HVAC or a small AC unit.

Don't try to power EVERYTHING. The whole point of a portable generator is to keep critical things running, not to replace your full electrical service.

Generator Safety: A Critical Section

Generators kill people every year, mostly through carbon monoxide poisoning. Operating procedures matter.

NEVER run a generator inside a garage, basement, or any enclosed space. Even with the door open, CO accumulates. People die every year doing this.

Operate portable generators outdoors, at least 20 feet from homes and buildings, with exhaust directed away from doors, windows, and vents. Wind can carry exhaust toward the house.

Have a CO detector in the house, and check the batteries before generator season.

Don't refuel a hot generator. Let it cool first. Spilled gas on a hot engine can ignite.

Don't backfeed the panel without an interlock. Plugging a generator into a regular outlet to feed the rest of the house is illegal AND extremely dangerous: the generator's voltage can travel back to the utility lines, killing utility workers who don't know there's a "live" line.

Use only outdoor-rated extension cords, or proper generator cords for the installed inlet.

Keep The Generator Dry. Follow the manufacturer's instructions for wet-weather use and shock protection. A cover or canopy is not proof that the location is safe; never use a porch, carport, garage, or enclosed space.

Standby Generators (Whole-House)

The other approach: a permanently-installed generator that starts automatically when utility power fails.

Components:

• Generator unit: usually 14–26 kW (kilowatts)
• Automatic Transfer Switch (ATS)
• Fuel supply: natural gas (preferred for residential; no fuel storage) or propane (with a tank)
• Concrete pad for the generator
• Conduit and wiring between generator, ATS, and main panel

Installation:

This is genuinely a professional project for several reasons:

1. Fuel system work. Connecting natural gas requires a licensed gas fitter (or licensed plumber in some jurisdictions). Pulling a permit for gas work is separate from the electrical permit.
2. ATS sizing and installation. The ATS must be sized to the home's main service. Installation involves cutting into the service entrance, which requires utility coordination.
3. Engineering. The generator must be sized to handle the home's anticipated peak load, with margin for motor starting currents.
4. Multiple inspections. Electrical, gas, and sometimes structural inspections.
5. Warranty considerations. Most generator manufacturers (Generac, Kohler, Briggs & Stratton) require professional installation for warranty coverage.

DIY is technically possible but rarely worthwhile. The cost savings ($1500–3000 of labor) are offset by the time investment (40+ hours), the risk of doing fuel work incorrectly, and the warranty implications.

If you want a standby generator, getting bids from 2–3 reputable contractors is the right path. Costs vary widely:

• 14 kW unit, basic installation: $5,000–7,000
• 20 kW unit, more circuits covered: $7,000–10,000
• Whole-house automatic, 22+ kW: $10,000–15,000+

Maintenance: Both Types

Portable generators:

• Run for 30 minutes monthly to keep fuel circulating and prevent cylinder issues.
• Change oil per the manufacturer's schedule (often every 50–100 hours of running).
• Drain fuel before extended storage (fuel goes stale within 6 months).
• Check air filter and spark plug annually.
• Run a simulated outage drill once a year so you remember the procedure.

Standby generators:

• Most have auto-exercise modes that run the engine briefly each week.
• Annual professional service is recommended (oil change, filter, plugs, transfer switch test).
• Check the unit visually after major weather events.
• Address any error codes promptly.

Code Considerations

A few NEC items specific to generators:

Article 702: Optional Standby Systems. Covers standby generator installations.

Section 702.5: Capacity and rating. The generator's capacity must be appropriate for the loads it's intended to serve.

Section 702.6: Transfer equipment. ATS or interlock must be listed and installed correctly.

Section 702.11: Outdoor generator sets. Specific siting requirements (clearances from structures, ventilation).

GFCI requirements. Recent NEC editions have expanded GFCI requirements; some generator outlet circuits and ATS connections may require GFCI protection.

Identification. Generator-fed outlets and circuits should be identified per NEC requirements.

Common Mistakes

Backfeeding without an interlock. As mentioned, this is dangerous and illegal. Don't do it.

Undersizing the generator. Buying a 4,000W unit and trying to run a refrigerator, well pump, AC, and microwave simultaneously. The generator will trip its overload protection and possibly damage itself.

Operating the generator in an enclosed space. CO kills.

Skipping maintenance. A generator that hasn't been run in 18 months may not start when you need it.

Connecting to a panel without inspection. Permitted DIY installations should always be inspected. The costs of skipping are high.