How Long Does Installation Take?#
A complete standby generator installation — from signing the contract to the generator running under load — typically takes 4 to 12 weeks for residential and light commercial projects. The variance comes almost entirely from permitting and utility coordination, not from the physical installation work.
The physical work itself, once permits are in hand and equipment arrives, typically takes 2 to 4 days for a 20–100 kW residential or small commercial installation. Here is what each phase involves.
Phase 1: Site Assessment and System Design (1–2 Weeks)#
Before anything is ordered, a site assessment establishes what the installation requires:
- Load analysis: determining which circuits need to be backed up and the total connected load (kW)
- Fuel assessment: confirming gas meter capacity for natural gas installations, or identifying the best tank location and containment requirements for diesel/propane
- Placement survey: identifying a code-compliant location for the generator — NFPA 37 requires minimum clearances from building openings (windows, doors, air intakes), property lines, and combustible materials
- Electrical assessment: evaluating the main panel configuration and identifying the optimal transfer switch location and configuration
- Utility coordination: for natural gas, confirming the service pressure and line size can support the generator's gas consumption at rated load
The output of this phase is a system design document that specifies the generator model, transfer switch type and rating, fuel system configuration, and pad/mounting requirements. This document becomes the basis for the permit application.
Phase 2: Permits and Approvals (2–6 Weeks)#
This is the phase that most affects timeline. California requires building permits for permanent standby generator installations, and additional permits or registrations apply in most cases:
Building permit — required for the generator mounting, electrical work, and gas piping. Issued by the local building department (city or county). Plan review typically takes 2–4 weeks for residential permits; 4–8 weeks for commercial.
Electrical permit — covers the transfer switch installation and any panel modifications. Often issued concurrently with the building permit or as a sub-permit.
Gas permit — if gas line modification is needed (common for larger generators or when the existing service needs upgrading), a separate gas permit may be required.
Air quality registration — in California, generators above certain output thresholds require registration with the local Air Quality Management District (AQMD). In most districts, this is a registration process, not a formal permit review, but it must be completed before the generator is put into service.
Utility notification — for automatic transfer switch installations, most California utilities require notification before the ATS is energized. PG&E, for example, requires a completed interconnection form for permanent standby generator installations.
For luxury residential installations at estates in Los Altos Hills, Hillsborough, Atherton, Woodside, or similar jurisdictions, design review board approval may add 2–4 additional weeks if the generator pad or enclosure is visible from a public street.
Phase 3: Site Preparation (1–2 Days)#
Site preparation typically begins while permits are being processed, for work that does not require a permit (rough grading, utility locates, material staging) or following permit issuance.
Generator pad: Most standby generators are mounted on a concrete pad, poured to the manufacturer's dimensional requirements and reinforced to support the generator's operating weight (typically 1,000–4,000 lbs for 20–100 kW units). The pad must be level, above any local flood elevation, and set back per NFPA 37 clearance requirements.
Some installations use pre-fabricated composite pads, which can be placed the same day as the generator delivery. These are acceptable for most residential and light commercial applications.
Conduit and wiring rough-in: The electrician runs conduit from the main panel location to the transfer switch location and from the transfer switch to the generator pad before the generator arrives. This work is inspected by the building department in most jurisdictions before it is covered or buried.
Gas line extension: If the existing gas service requires extension or upsizing to reach the generator location, this work is done before generator delivery. Gas line work requires a licensed plumber or gas contractor in California, and the work must pass gas pressure test inspection before being put into service.
Phase 4: Generator Delivery and Mechanical Installation (1 Day)#
Generator delivery for most small commercial and residential units is a truck delivery with a liftgate or boom truck — no crane is required for generators under approximately 8,000 lbs. Larger commercial units (200 kW+) may require a crane or specialized lift equipment, which is coordinated with the delivery.
Once on-site, the installation crew:
- Places the generator on the prepared pad and anchors it to the pad per manufacturer requirements and local seismic bracing standards (California requires seismic anchorage per the California Building Code)
- Connects the exhaust system — typically a flexible exhaust connector and stainless steel flue that exits through the enclosure or building wall
- Makes the fuel connections — gas line final connection by licensed gas contractor; diesel fill connection to day tank by the installation crew
- Connects the generator battery and battery charger
- Pulls and terminates control wiring between the generator and transfer switch
Phase 5: Electrical Work and ATS Installation (1 Day)#
Transfer switch installation is the most complex electrical task in the project. The process:
- Utility disconnect — the electrician coordinates with PG&E (or the local utility) to disconnect service at the meter while the transfer switch is being installed in the main panel
- Transfer switch wiring — the ATS is wired between the utility service entrance and the load panel(s) to be backed up. The specific configuration (whole-panel transfer vs. critical circuits only) was determined in the design phase
- Generator connection — the generator output wiring is terminated at the ATS generator terminals
- Control wiring completion — the communication circuit between the ATS and generator control panel is completed
For luxury residential installations, the ATS may be a whole-home transfer switch rated for the full service entrance (typically 200–400A for estate properties), with automatic selective load management to prioritize loads during transfer.
Phase 6: Commissioning (Half Day)#
Commissioning is the process of starting the system for the first time and verifying that everything works correctly together. A properly commissioned installation includes:
- Initial start: generator started and run at no load to verify oil pressure, coolant temperature, voltage, and frequency within specification
- Transfer test: utility power interrupted to simulate an outage; ATS transfer time measured and verified against specification (typically 10–30 seconds)
- Load acceptance test: generator loaded to at least 25–50% of rated capacity while monitoring voltage, frequency, and engine temperatures
- Retransfer test: utility power restored; ATS retransfer verified; generator shut down and cool-down cycle confirmed
- Exercise timer programming: automatic weekly or monthly exercise cycle programmed into the generator control panel
- Walkthrough: installer walks through generator controls, how to check oil and coolant, what the LED indicators mean, and what to do if the generator does not start automatically during an outage
A commissioning report should be provided documenting the test results. This report also serves as the baseline record for your maintenance log.
Phase 7: Inspection and Final Permit Closeout (1–2 Weeks After Install)#
Most jurisdictions require a final inspection of the completed installation before the permit is closed. The building inspector will verify:
- Generator is mounted and anchored per the approved plans
- Electrical work matches permitted drawings
- Gas connections pass a pressure hold test
- Required clearances are maintained
- Required safety labels are affixed to the generator and transfer switch
After the final inspection passes, the permit is closed and your installation record is complete.
First Maintenance Visit#
Plan your first scheduled maintenance visit 6–12 months after commissioning, or after the generator's first 50 hours of runtime (whichever comes first), per most manufacturers' break-in service schedules. This initial service includes:
- Oil and filter change (break-in oil change removes metal particles from initial engine wear)
- Air filter inspection
- Coolant concentration check
- Battery condition check
- Transfer switch operation verification
- Review of any fault codes logged since commissioning
After the break-in service, your generator transitions to a standard maintenance schedule — typically one or two visits per year depending on runtime hours.
Ready to begin? Contact our team for a site assessment and proposal, or explore generator options for residential and commercial installations across the Bay Area and Northern California.