Automatic Transfer Switches — Emergency Build & Same-Day Stock

When utility power fails, the automatic transfer switch is the device standing between your facility and downtime. We stock and build automatic transfer switches (ATS) from 100A to 4000A, in 3-pole and 4-pole configurations, ready to ship inside 24 to 48 hours when manufacturer lead times are 20+ weeks. If your distributor is quoting you a Q4 ship date and your generator is sitting idle, this is the page for you.

Our automatic transfer switch inventory covers the brands engineers actually specify: ASCO Series 300, 4000, and 7000, plus Russelectric, Eaton, Cutler-Hammer, GE Zenith, Siemens, and Caterpillar transfer switch equipment. Open transition, closed transition, and delayed transition variants. Service entrance rated and non-service entrance rated. Request a quote and we will confirm stock the same business day.

What an Automatic Transfer Switch Does

An automatic transfer switch monitors incoming utility power and, when voltage or frequency falls outside acceptable tolerances, automatically transfers the load to a standby generator. When utility power is restored and stabilises, the ATS transfers the load back and signals the generator to shut down through its cool-down cycle.

The ATS is the load-side coordinator of every standby power system. It prevents backfeeding into the utility grid (a critical safety function for utility line workers), enforces break-before-make or make-before-break logic depending on transition type, and integrates with the generator controller, paralleling switchgear, and any downstream distribution equipment. Without an ATS, a generator and its load are simply two electrical sources with no way of safely coexisting.

For commercial and industrial facilities, the ATS is not optional. NFPA 110, the National Electrical Code (NEC), and most local Authority Having Jurisdiction requirements mandate an automatic transfer switch on any permanently installed standby or emergency power system.

Transition Types — Open, Closed, and Delayed

The transition type determines how the ATS handles the moment of transfer between utility and generator. Choosing the right one matters because it directly affects load behaviour during the switch.

Open Transition (Break-Before-Make)

The most common configuration. The ATS opens the utility connection before closing the generator connection, producing a brief power interruption (typically under one cycle) during transfer. Acceptable for lighting, HVAC, motors, and the majority of commercial loads. Lower cost and simpler control logic.

Closed Transition (Make-Before-Break)

Both sources are momentarily paralleled during transfer, producing no interruption to the load. Requires synchronisation between utility and generator. Specified for data centers, hospital operating theatres, broadcast facilities, and any load where even a sub-cycle dropout is unacceptable. Higher cost, more complex protective relaying.

Delayed Transition

An open-transition variant with a programmed off-time between disconnecting one source and connecting the other. Used to allow large motor loads to decay before reconnection, preventing the inrush damage that would occur with an immediate transfer. Common on water treatment pumps, HVAC chillers, and elevator motor loads.

Amperage and Pole Configurations

We stock automatic transfer switches across the full commercial and industrial range:

• 100A – 400A: Light commercial, small medical clinics, branch telecom sites, light industrial.
• 600A – 1200A: Mid-size commercial buildings, distribution centers, regional data centers, multi-tenant office.
• 1600A – 2500A: Hospitals, large industrial facilities, manufacturing plants, water treatment.
• 3000A – 4000A: Hyperscale data centers, heavy manufacturing, utility substations, critical infrastructure backbones.

3-pole switches are used on 3-phase systems where the neutral is solidly grounded and is not switched. 4-pole switches (with neutral switching) are required when the standby source is a separately derived system or when local code requires neutral isolation between sources, which is increasingly common on healthcare and data center installs. Both are available across all amperage tiers, 120/208V through 480V and 480/277V.

Service Entrance Rated vs Non-Service Entrance Rated

A service entrance rated ATS is built to function as the main service disconnect for the building, with integrated overcurrent protection and the labelling required by NEC Article 230. This eliminates a separate service disconnect upstream, reducing equipment count and installation cost on new builds.

A non-service entrance rated ATS is installed downstream of an existing service disconnect, which is typical on retrofit projects where the main switchgear is already in place. Both configurations are available in our ASCO, Russelectric, and Eaton inventory.

Where Automatic Transfer Switches Are Used

Any facility that cannot tolerate a sustained utility outage runs an ATS. The applications we ship to most often:

• Hospitals and healthcare: NFPA 110 Level 1 emergency systems, surgical suites, ICU, life-safety branch circuits.
• Data centers: UPS-backed critical loads, mechanical cooling redundancy, multi-source N+1 and 2N topologies.
• Manufacturing: Continuous process lines, semiconductor fabs, cleanrooms, batch chemical operations.
• Telecommunications: Central offices, cell tower hub sites, fibre regeneration huts.
• Water and wastewater treatment: Pump stations, lift stations, chlorination and filtration plants.
• Cold storage and logistics: Refrigerated warehouses, food distribution centers, pharmaceutical cold chain.
• Critical commercial: Financial trading floors, broadcast studios, emergency operations centers, 911 PSAPs.

Standards and Code Compliance

Every automatic transfer switch we ship is built or sourced to meet the standards that matter on commercial and industrial projects:

• UL 1008: The Standard for Transfer Switch Equipment. Required for emergency, legally required standby, and optional standby applications under the NEC.
• NFPA 110: Standard for Emergency and Standby Power Systems. Defines transfer time, testing, and inspection requirements by system level (Level 1 for life safety, Level 2 for less critical loads).
• NEC Articles 700, 701, 702, 708: Emergency systems, legally required standby, optional standby, and critical operations power systems respectively.
• NEMA enclosure ratings: NEMA 1 (indoor general purpose), NEMA 3R (outdoor weatherproof), NEMA 4X (corrosion resistant, often spec’d for water treatment and coastal industrial sites).

Why Source Your ATS Through Us

The ATS market has two failure modes. Either you order new from the manufacturer and wait 20 to 30+ weeks for delivery, or you scramble for surplus inventory of unknown provenance. Neither works when your project deadline is next month and your generator is already on site.

We solve that with stocked, tested, brand-name automatic transfer switch inventory shipped in 24 to 48 hours. Every switch we sell is electrically tested, mechanically verified, and supplied with documentation. We work with electrical contractors, facility managers, EPC firms, and end users across hospitals, data centers, industrial manufacturing, telecom, water treatment, and critical commercial sites nationwide.

If you need a specific configuration we don’t have on the shelf — a particular ASCO Series, a 4-pole at a specific amperage, a service entrance rated unit with a specific enclosure — our build team can configure and ship inside the same emergency window. Closed transition, delayed transition, bypass-isolation, custom enclosures, integral surge protection: we have built them all.

Request a Quote

Send us the basics — amperage, voltage, pole configuration, transition type, brand preference if you have one, and your required ship date — and we will respond the same business day with stock confirmation and pricing. If we have it, we can have it on a truck within 48 hours. If we need to build it, we will tell you exactly when, with no padded lead times and no surprise extensions. Contact us through the quote form on this page or reach our team directly to start the conversation.