Commercial Electrical Services · Pillar Guide

Commercial backup power that keeps you open during outages.

Standby generators, automatic transfer switches, and the PSPS-resilience design that determines whether your business stays open during multi-day outages.

Written bySteven Lockhart

Reviewed byAlex Towery · C-10 #989290

Updated: June 2026 · Read: 7 min

11 yrsMarin electrical work

C-10CSLB licensed contractor

1st passInspection rate

48 hrTypical estimate turnaround

Key Takeaways

PSPS exposure in Marin and Sonoma drives 60-70% of commercial generator inquiries — outages of 24-72+ hours have happened in 6 of the last 8 fire seasons.
Commercial generators are sized for whole-facility load (typically 30-150kW range for Marin small-to-mid commercial) — much larger than residential 18-22kW units.
Natural gas is the default fuel for in-town commercial installations; propane or diesel for properties without natural gas service.
Three-phase Automatic Transfer Switches are required for most commercial generator installs — different scope from residential ATSs.
Annual maintenance and load-bank testing are essential for commercial standby — generators that haven't been exercised under load are not actually reliable backup.

Towery Electric — Commercial Backup Power.

01 — OverviewWhat Commercial Backup Power actually covers in Marin.

Commercial backup power planning in Marin starts with a question: what does your business cost per hour when you're closed? For restaurants, the answer is typically $400-$1,200 per hour during operating hours. For retail, $200-$800 per hour. For professional services with appointment-driven revenue, the cost can be much higher when including reputation damage from cancelled commitments. A 36-hour PSPS event without backup power costs most Marin businesses $8,000-$45,000+ in direct lost revenue.

The economic case for commercial backup power is straightforward — typical installs ($28,000-$85,000 for 30-50kW units serving small commercial properties) pay back in one or two avoided PSPS events. The technical work is more complex than residential — three-phase service, larger fuel storage, ATS sizing for commercial loads, annual exercising under load.

Definition

Commercial backup power covers the design, installation, and maintenance of standby generators and automatic transfer switches sized for commercial property loads — typically 30-150kW range for small-to-mid Marin commercial, with three-phase ATSs and dedicated fuel supply.

Sizing commercial generators

Sizing depends on what you want to back up. Full-facility backup requires generator sized for total connected load plus startup surge (typically 1.5-2x the steady-state load). Critical-circuits-only backup uses a smaller generator and a transfer switch that powers only essential systems (POS, refrigeration, basic lighting). The latter is 40-60% cheaper but requires careful selection of critical vs non-critical loads.

Fuel supply planning

Natural gas is the cleanest fuel for in-town commercial — no on-site storage required, fuel delivery is automatic via gas utility. Propane requires on-site tank (typically 500-1000 gallon for commercial sizes) but works at properties without natural gas. Diesel is used on larger industrial applications and provides extended runtime.

For the broader context this guide supports, see our Commercial Electrical Services overview.

Explore the Full Guide

Commercial backup power clusters by sizing approach, fuel choice, and use case. This pillar links to scope-specific guides.

Three guides to read first

Cornerstone

Commercial Standby Generator Process

How a Marin commercial backup power install actually goes — sizing through PG&E coordination through commissioning.

Explore the guide →

Sizing

Whole-Facility vs Critical-Circuits Backup

How to choose between sizing for full-facility backup or critical-circuits-only.

Explore → PSPS

Commercial PSPS Resilience Planning

How to design a backup power system that handles multi-day PSPS events.

Explore →

Browse the Full Library

By generator size

Fuel & supply

By use case

Maintenance & monitoring

02Commercial generator sizing and cost by category.

Pricing scales with generator capacity, fuel infrastructure, and ATS complexity. Range reflects 2026 Marin commercial install data.

Generator size	Typical use	Install cost range
22-30kW	Small retail, coffee shop	$22,000 to $38,000
30-50kW	Restaurant, mid-size retail	$32,000 to $58,000
50-100kW	Full-service restaurant with bar	$54,000 to $95,000
100-150kW	Medical office, larger commercial	$85,000 to $165,000
150kW+	Multi-tenant or specialty	$140,000+ (project-specific)

03Whole-facility vs critical-circuits — the decision framework.

Most commercial generator decisions come down to this choice. Each has a different cost and capability profile.

Whole-facility backup

Generator sized for total connected load. Everything runs during outage — full lighting, full HVAC, full equipment. Cost is higher; convenience is total. Right for: restaurants where partial operation isn't viable, medical offices, retail with refrigerated inventory.

Critical-circuits backup

Generator sized for essential systems only (POS, refrigeration, key lighting, security). 40-60% lower install cost; full-facility loads stay off during outage. Right for: offices that can run on partial capacity, retail without refrigeration, professional services.

04PSPS resilience — what 'extended outage' actually means.

PSPS events in Marin and Sonoma have run 12-72+ hours in recent years. Generator sizing has to account not just for connected load but for runtime — a generator that can power your facility for 8 hours but runs out of fuel at hour 9 doesn't actually solve the PSPS problem. For natural gas systems, fuel supply is generally not a concern (utility gas service typically continues during electric PSPS). For propane or diesel systems, on-site fuel storage is sized to expected outage duration plus margin.

Annual maintenance and load-bank testing matter enormously for actual reliability. Generators that haven't been exercised under load for 12+ months frequently fail when first asked to operate at full capacity during a real outage. We schedule annual load-bank testing for every commercial client on a service contract — it's the difference between 'backup power on paper' and 'backup power that actually works.'

05Annual commercial generator maintenance — what it actually includes.

Commercial standby maintenance is more involved than residential. Three key components.

Engine service

Oil change, filter replacement, coolant check, fuel-system inspection. Typically every 100-200 hours of operation or annually, whichever comes first. Cost: $400-$900 per visit depending on generator size.

Load bank testing

Generator runs under simulated full load for 30-60 minutes to verify it can actually deliver rated power. Critical for catching issues that don't show during the unloaded weekly self-test. Cost: $800-$1,800 per test annually.

Frequently Asked Questions

How much does a commercial generator cost in Marin?

For a typical Marin small-commercial install (30-50kW for restaurants and mid-size retail), expect $32,000-$58,000 all-in including generator, three-phase ATS, gas hookup, pad, PG&E coordination, AHJ permit, and commissioning. Larger systems scale from there: 50-100kW runs $54,000-$95,000; 100-150kW for medical office and larger commercial runs $85,000-$165,000. Critical-circuits-only systems run 40-60% lower than whole-facility for the same connected business.

How long does a commercial generator install take?

For a typical 30-50kW commercial install, expect 8-14 weeks from contract to commissioning. The phases: permit issuance (1-3 weeks), generator and ATS lead time (4-8 weeks for typical Generac/Kohler sizes), pad and electrical infrastructure work (2-3 weeks), PG&E coordination for ATS install (1-2 weeks), commissioning and load testing (3-5 days). On-site work is concentrated; lead times dominate the timeline.

Should we get whole-facility or critical-circuits backup?

It depends on what closing your business during a PSPS event would cost. Whole-facility backup is right for businesses where partial operation isn't viable: restaurants (you can't operate without kitchen + walk-ins + dining lighting), medical offices, retail with significant refrigerated inventory, or businesses with continuous customer presence. Critical-circuits is right for businesses that can run on partial capacity: offices (POS/IT + minimal lighting), retail without refrigeration, professional services. Most Marin restaurants choose whole-facility; most professional services choose critical-circuits.

What fuel should our commercial generator use?

For Marin in-town commercial properties, natural gas is the default. No on-site storage required, fuel delivery is automatic via PG&E gas service (which typically continues during electric PSPS events), simpler permit pathway. Propane is the answer for properties without natural gas service — requires on-site tank (typically 500-1000 gallon for commercial). Diesel is used on larger industrial applications (150kW+) for extended runtime and cooler operating characteristics.

How often does a commercial generator need maintenance?

Annual at minimum, with additional service after any extended-runtime event. Annual maintenance includes engine service (oil, filters, coolant, fuel system inspection), full electrical inspection of the ATS and emergency circuits, load-bank testing (generator runs under simulated full load for 30-60 minutes to verify it can deliver rated power), and battery service for the start system. Commercial annual maintenance contracts run $1,400-$3,200 depending on generator size. Skipping maintenance is the biggest preventable cause of generator failure during real outage events.

Will our generator handle a multi-day PSPS?

With natural gas: yes, indefinitely as long as gas service continues (which is typical even during electric PSPS — gas utility service is generally unaffected). With propane: depends on tank size. A 1000-gallon propane tank powers a typical 50kW commercial generator for roughly 5-7 days at average load. We size on-site propane storage to expected PSPS duration plus margin (typically 7-10 days for Marin/Sonoma). For longer runtime scenarios, we coordinate emergency propane delivery as part of the service contract.

How We Reviewed This Page

Reviewed against current California Electrical Code (Title 24, Part 3) and 2023 NFPA 70 (NEC) provisions applicable to the topic.
Pricing ranges reflect actual 2026 Towery Electric quote data from Marin County jobs — not third-party industry averages.
Permit and inspection timing reflects current AHJ practice in Novato, San Rafael, Mill Valley, and unincorporated Marin County as of mid-2026.
Technical review by Alex Towery, founder and C-10 #989290 holder, with 11+ years of California electrical work.
All factual claims about code requirements were verified against primary sources (CSLB, CARB, PG&E, AHJ) at time of publication.

References

This guide reflects Towery Electric's professional standards as a California-licensed C-10 electrical contractor and is for general information. Site conditions, panel configurations, code amendments, and permit-authority requirements vary; final scoping, sizing, and code compliance for your specific address are determined on a paid site assessment. We follow California Electrical Code (Title 24, Part 3) and applicable NFPA 70 (NEC) editions adopted by your AHJ.