ASCO 300 Series ATS

Frequently Asked Questions

What is the ASCO 300 Series amperage range?

70 to 3000 amps. The 70-400A bracket uses contactor-style switching listed to UL 1008. The 600-3000A bracket uses power-frame switching listed to UL 891. Voltage rating is 600 VAC max, 50 or 60 Hz, single or three phase.

What is the difference between the ASCO 300 Series and 7000 Series?

Both are open-transition transfer switches. The 7000 Series is ASCO's current premium / mission-critical line with closed-transition, soft-load, and bypass-isolation options, plus the QuickConnect feature for hot-plug servicing. The 300 Series is the cost-optimized commercial line — same base reliability, fewer optional features. For data centers, hospitals, and other code-driven mission-critical loads, spec the 7000. For standard commercial backup, the 300 Series is more than adequate.

Is the 300 Series service-entrance rated?

Yes — the 300SE variant is UL 1008 service-entrance rated, allowing the ATS to function as the main service disconnect. This eliminates a separate main breaker upstream and is common in light-commercial and small-multi-family installs where panelboard simplicity matters.

Does the 300 Series do closed-transition transfer?

No — the 300 Series is open-transition only. Closed-transition (paralleling utility and genset for sub-100ms during transfer to avoid load interruption) is available on the ASCO 7000 Series. If your load cannot tolerate even a brief interruption during retransfer, you need a 7000-series unit or a UPS bridge.

What gensets typically pair with the ASCO 300 Series?

Any genset with auto-start signaling. At smaller amperages (70-200A), it's commonly paired with 30-150 kW gensets like the Kohler KG60, Cummins QSB7-based DSGAA-DSGAE, and Generac Industrial SG080. At larger amperages (600-3000A), it pairs with mid-to-large diesel platforms (Cummins QSL/QSX, Caterpillar C9-C32). The 300 Series can also be specified as a downstream ATS in a multi-tier transfer scheme.

What controller does the ASCO 300 Series use?

Standard is the ASCO Group G controller — a fixed-function microprocessor controller covering all common AMF features (timers, alarms, exerciser, retransfer logic). For more advanced needs (programmability, expanded comms, color HMI), the 4000 Series moves to the Group 5 controller, and the 7000 Series uses Group 7.

What's the typical lifespan of an ASCO 300 Series ATS?

30+ years of service life with proper maintenance. The contactor mechanism is mechanically robust; the most common service item is the controller (some early Group G units had electrolytic capacitor failures around year 15-20). Annual exercise and load-bank testing identify wear long before failure.

Service Specifications

Key Terms

Open-transition transfer

Brief (typically 100-500ms) interruption between disconnect from one source and connect to the other. Standard for commercial backup.

Closed-transition transfer

Brief (typically <100ms) parallel of utility and genset during transfer, eliminating load interruption. Requires utility coordination and genset paralleling capability.

Service-entrance rated (SE / 300SE)

ATS approved by UL to function as the main service disconnect for a building, eliminating the need for a separate main breaker upstream.

Contactor switching vs power-frame

70-400A units use electromagnetic contactor switching (fast, simple). 600-3000A units use mechanically-held power-frame switches (more robust at high current).