Commercial ATS: generator integration done right.
Commercial ATS integrates the generator with building electrical service — automatic switching, monitoring, programming. Sizing and configuration affect reliability.
By Steven Lockhart · Reviewed by Alex Towery, C-10 #989290
Updated 2026-06-16
Commercial ATS install scope: ATS sized for service amperage (200A, 400A, 600A, 800A, 1200A typical), configuration (open transition, closed transition, or hybrid based on application), generator integration wiring (signal, control, sensing), service entrance modification or feeder connection, monitoring and control panel integration, commissioning. Marin commercial install $8,000-$45,000+ depending on ATS size and integration complexity. Often integrated with commercial generator project scope.
01How commercial ATS differs from residential.
Commercial ATS units are physically larger, electrically more capable, and more programmable than residential equivalents. Size ranges 100A to 5,000A+ (vs 200A typical residential). Programming options include voltage and frequency thresholds, transfer timing, exercise scheduling, load sequencing for restart, monitoring integration. Commercial ATS commonly has communication ports (Modbus, BACnet, Ethernet) for building management system integration.
Open transition vs closed transition: open transition (the standard configuration for residential and most commercial) drops load momentarily during transfer (typically 100-500 milliseconds). Closed transition parallels generator with utility briefly during transfer (under 100ms), giving truly uninterrupted transfer at the cost of more complex generator parallelism (requires generator that can paralleled with utility, requires utility coordination). Closed transition is sometimes specified for critical loads where any momentary interruption is unacceptable.
02Sizing and configuration.
Service entrance ATS
ATS sized for full service amperage, located after meter and before main distribution. Routes entire building between utility and generator. Most common configuration.
Distributed ATS
Multiple smaller ATS units, one per major load category. Generator feeds a 'critical loads bus' through smaller ATS units selectively. More flexibility, more complexity.
Programming considerations
Transfer timing (delay before generator takeover, delay before retransfer), exercise schedule (frequency, duration, with/without load), monitoring and alerts, sometimes integration with building management.
03Marin commercial deployments.
Common installations: 400A or 600A ATS for typical commercial building, 800A-1200A for larger facilities, 200A ATS for smaller commercial or specific critical-loads subset. Brand selection often dictated by generator manufacturer — Generac generators paired with Generac ATS, Cummins with Cummins, etc. Independent ATS brands (ASCO, Russelectric, Cummins) work with any generator make.
Code compliance: ATS for emergency systems (NEC 700) requires UL 1008 listing, automatic operation, specific labeling. For legally required standby (NEC 701) and optional standby (NEC 702), similar but slightly relaxed requirements. We specify ATS appropriate for system category and code requirements. Permitting and inspection scope includes ATS installation; inspectors verify proper integration and operation.
Common questions.
Can existing ATS be reused for new generator install?
Sometimes. If existing ATS is sized appropriately and in good condition, it can be retained. Common scenario: old generator being replaced with new generator of similar size — ATS may be reusable. Often new generator install also includes new ATS because integration is cleaner (matched manufacturer, current technology, fresh warranty). Cost-benefit assessment during planning identifies best approach.
How long does ATS install take?
Per ATS: 1-2 days install typically. Includes ATS mounting, electrical connections (utility side, generator side, load side), generator interface wiring, programming, testing. Larger ATS (800A+) sometimes 2-3 days. Total project including planning, permit, install, commissioning: 4-8 weeks typical.
What about manual bypass for maintenance?
ATS bypass switch allows ATS to be bypassed (taken out of service) for maintenance without losing utility power to the building. Useful for medium and large commercial installations where ATS maintenance can't justify building shutdown. Adds modest cost ($2,000-$8,000 depending on size) but valuable for serviceability. Required for some emergency power applications per NFPA 110.
How is ATS tested?
Initial commissioning: simulated utility failure (open the utility-side breaker briefly), verify ATS transfers to generator within spec timeframe, verify load is restored, verify retransfer when utility returns. Periodic testing: monthly or quarterly per maintenance schedule. Annual full functional test for NFPA 110 emergency systems. Testing is part of ongoing maintenance contract scope.
How do you handle pricing — flat fee or hourly?
Both, depending on scope. Routine service calls and predictable scope (panel replacement, EV charger install, transfer switch install, fixture replacement) are flat-fee quoted up front. Diagnostic visits and emergency scope are hourly because we don't know what we'll find. Either way, you get a written quote before work starts on anything significant, and we don't proceed beyond the quote without your sign-off.
How quickly can you schedule?
Depends on scope and season. Emergency dispatch: same-day across Marin County (1-3 hours business hours, 1-4 hours after-hours). Same-day standard service: 3-6 hours from call when capacity allows; otherwise next business day. Scheduled service work: 1-3 weeks typical. Larger projects requiring permits and PG&E coordination: 4-12 weeks depending on scope. We're upfront about timeline at the quote stage.
What warranty do you offer on work?
Our standard residential warranty: 2 years on labor, manufacturer warranty on parts (varies by product — typically 1-10 years). Major installs (panels, generators, EV chargers) often have longer manufacturer warranties (5-10 years). If there's an issue with our work in the warranty period, we come back and fix it at no cost. We also stand behind work past warranty — repeat customers and referrals matter more than a transactional fix.
Are you licensed and insured?
Yes. California State License Board C-10 Electrical Contractor #989290, in good standing. Carry general liability insurance and workers' compensation insurance as required by California law. Bondable on projects requiring it. Happy to provide proof of insurance to clients or property managers on request. License lookup: cslb.ca.gov.
Talk to a licensed electrician in Marin.
Family-run, C-10 #989290, 20+ years in the trade. Honest scoping, fair pricing, work that lasts.