Standby generator installation: the electrical work

Who does which part

A standby generator is a three-trade job. The pad and the unit are set by the installer. The electrician handles the transfer switch, the wire and conduit between the unit and the house, the grounding and bonding, the labels and the panel work. A gas or plumbing contractor runs the fuel line. CSLB’s plumbing class, C-36, lists gas piping and gas connections, while the C-10 electrical class covers wires, raceways and conduits. Ask every bidder to write down who does what, so nothing falls between the two.

The typical SoCal range for the electrical hookup is about $1,500 to $3,000 as of October 2026, with the generator extra (see the standby generator hookup cost page). The gas line is a separate bid.

Transfer switch: automatic, and why

An automatic transfer switch (ATS) watches the utility voltage. When power drops, it signals the generator to start. It then moves the chosen circuits to the generator and keeps the grid and the generator from ever being connected at the same time. When the grid returns, it moves back and the generator shuts down.

That lockout matters. Ameren’s safety notice warns that a generator connected the wrong way can re-energize power lines and put utility crews, first responders and the public at risk. An ATS removes the step where a person could make that mistake.

If you run a portable generator by hand, a manual setup is enough. The interlock kit page and the inlet box page cover that route, and the transfer switch page compares manual and automatic units.

Whole house or chosen circuits

Two layouts are common. A whole-house switch passes the entire service through the ATS. A circuits-only setup puts the loads you care about, such as the refrigerator, furnace fan, lights and internet, on a critical loads subpanel and feeds only that panel.

The choice drives the size of the generator, the switch and the wire. It also changes the price. A smaller generator can run a circuits-only layout. Air conditioning, electric ovens and dryers are what push a whole-house layout to a larger unit.

Sizing the generator

Sizing follows NEC Article 702, which covers optional standby systems. In the 2025 EC&M explainer of the article, a manual connection should be sized for all the loads meant to run at once. For automatic connection, the system must carry the full load that is connected automatically, unless an approved energy management system limits the load.

In plain terms, the electrician adds up the running watts, then checks the starting surge of the biggest motors, such as an air conditioner compressor or a well pump. The load calculation guide shows the method. Pick the loads first, then the generator, not the other way around.

Gas and fuel handoff

The electrician does not sign off the fuel side. Three points from city handouts show how much it matters to the schedule:

• Riverside County’s handout says the first inspection covers setbacks, conduit and the gas line, and the gas line is pressurized to 10 psi for that inspection.
• A new propane tank can require a fire department permit before the building permit is issued, per the same handout.
• Gas pipe size comes from the generator maker’s installation guide, which both handouts ask you to submit.

Ask the gas contractor early whether the existing meter and line can carry the added generator load. The handouts do not cover that question or how long a utility review takes, so ask the gas company directly.

Permits and what the city asks for

Standby generators are a plan-check item in the cities that published handouts. Expect these at submittal:

• A site plan showing the generator, transfer switch, conduit runs and fuel line
• Spec sheets and installation instructions for the generator and the switch
• A single-line electrical diagram with wire and conduit sizes, and grounding and bonding for a separately derived system
• The fuel type and gas pipe sizing
• A statement that 811 will be called before digging (Riverside County)

Fontana lists a disconnect on the generator for service, and signs at the service equipment that show the type and location of the standby source. Riverside County calls for a placard at the main panel and for new equipment to be listed for its use. Both are electrician items. Rules on which permits you need differ by city, so see electrical permits in Southern California.

Setbacks and noise

Fontana says generators may not sit in side yard setbacks or easements and may not be placed in hazardous locations. It sets exhaust outlet clearances of at least 10 feet to the property line, 3 feet to exterior walls or roofs and 10 feet to building openings. Riverside County asks for 5 feet to the property line, buildings and operable windows, and 5 feet of overhead clearance.

Those are two different answers for two nearby jurisdictions. Treat them as examples, not as your city’s rule. Noise is set locally as well: Fontana points to the property-line sound limits in its noise ordinance, and Riverside County asks the site plan to show barriers and refers to its noise ordinance. Ask the planning or building counter for your city’s handout before the site plan is drawn.

Panel limits and the 120 percent rule

If the generator feeds the house through a breaker in the panel, Fontana’s handout reminds applicants that the new breaker and the main breaker together may not exceed 120 percent of the bus rating. A panel that is full, old or already near its limit can fail this check. In that case a subpanel or a panel upgrade comes first.

Inspection

Riverside County’s handout describes two inspections. The first covers setbacks, conduit and the gas test. The second covers disconnects, wiring methods, grounding and bonding, the grounding electrode and labels. Other cities may split them differently.

When a battery fits better

A standby generator suits long outages and large loads, but it needs fuel, space and a neighbor-friendly spot. If you want quiet and automatic backup for a few essentials, compare it in the generator vs battery guide. For outages caused by wind and fire risk, see PSPS power shutoffs explained.

Businesses, multifamily common areas and sites with life safety loads follow different rules, including NEC Articles 700 and 701, air district permits and fire authority testing. They are covered on the commercial standby generator page.