Thomson Power Systems · TS920 Series (Commercial)

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Thomson TS920 Automatic Transfer Switch

Automatic Transfer Switches

Commercial automatic transfer switch. 100-400A, three-phase, open transition, contactor switching, TSC 9 controller. UL 1008 listed for emergency systems.

Overview#

The Thomson TS920 is the commercial counterpart to the residential TS910, offering contactor-based automatic transfer switching in the 100-400A range for commercial standby and emergency power applications. The critical distinction from the TS910 is the UL listing: the TS920 is UL 1008 listed for legally required emergency systems (NEC Articles 700/701), while the TS910 covers only optional standby (NEC 702). Both models are available in single and three-phase configurations. A service-entrance rated variant (TS920SE) is also available.

The TS920 uses the TSC 9 microprocessor controller with commercial-specific features for voltage sensing, programmable timers, and exercise scheduling. The three-phase 400A unit measures 45.1" x 24.9" x 11" and weighs 90 pounds in the standard NEMA 1 indoor enclosure. Both NEMA 1 indoor and NEMA 3R outdoor enclosures are available.

Where the TS920 fits in the Thomson lineup#

The TS920 bridges the gap between residential (TS910) and industrial (TS970) in Thomson's contactor-based ATS range:

For commercial loads under 400A that don't need Modbus or advanced controller features, the TS920 is the cost-effective choice. For loads above 400A or facilities requiring building automation integration, step up to the TS970.

Our service experience#

We see the Thomson TS920 most commonly in small Bay Area commercial installations — restaurants, small office buildings, and retail spaces in the 200-400A range. The contactor mechanism provides fast, reliable transfers, and the TSC 9 controller is straightforward to configure.

The 400A three-phase frame at 45.1" x 24.9" x 11" is compact enough for standard electrical rooms in commercial tenant improvements. At 90 pounds, it's light enough for a two-person install without mechanical handling equipment — a practical advantage over mechanically-held alternatives in tight retrofit spaces.

Frequently Asked Questions

What is the difference between the Thomson TS910 and TS920?
Both use the TSC 9 controller and contactor-based switching in 100-400A. While both are available in single and three-phase configurations, the critical difference is the UL listing scope: the TS910 is UL 1008 listed for optional standby systems (NEC Article 702), while the TS920 is UL 1008 listed for legally required emergency systems (NEC Articles 700/701). The TS920 also has higher three-phase withstand ratings. If the authority having jurisdiction requires emergency-system listing, you must specify the TS920.
What amperage ratings are available for the TS920?
The TS920 is available in 100A, 200A, and 400A ratings for commercial standby applications. All ratings carry 100% continuous current capacity and support both copper and aluminum power cable connections.
Does the TS920 support three-phase power?
Yes. The TS920 is a three-phase (3-pole) transfer switch available at 120/208V or 120/240V with 4-wire neutral. This makes it suitable for small commercial buildings with three-phase electrical service. For single-phase residential applications, use the TS910 instead.
What are the physical dimensions of the TS920?
The three-phase 400A unit measures 45.1 inches high by 24.9 inches wide by 11 inches deep and weighs 90 pounds in the standard NEMA 1 indoor enclosure. A NEMA 3R outdoor enclosure is also available. The rust-resistant aluminum enclosure is powder coated.
When should I choose the TS920 over the TS970?
The TS920 covers 100-400A with the simpler TSC 9 controller and is positioned for small commercial buildings. The TS970 covers 100-1200A with the TSC 900 controller (7-inch color touchscreen, Modbus, programmable I/O) and targets larger commercial and industrial applications. If you need more than 400A or require building management system integration via Modbus, specify the TS970.

Service Specifications

ServiceFrequencyNotes
Exercise under loadMonthlyRun generator and transfer load; TSC 9 has built-in exercise timer
Connection torque inspectionAnnuallyRetorque power lugs; especially important on 400A frames
Contactor inspectionEvery 5 yearsCheck contactor contacts for pitting; verify snap-action operation
Controller batteryEvery 5 yearsTSC 9 internal backup for clock and event log

Key Terms

Contactor switching
Electromagnetic switching mechanism that uses a coil to snap contacts closed. Fast transfer speed, compact size, and lower cost compared to mechanically-held designs.
Open-transition transfer
A brief (100-500ms) interruption between disconnecting from one source and connecting to the other. Standard for commercial backup applications.
4-wire with neutral
The TS920 three-phase configuration includes a solid (unswitched) neutral bus for 4-wire systems. The switched poles carry the phase conductors; neutral passes through on a dedicated bus.

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