Thomson Power Systems · TS970 Series (Commercial/Industrial)

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Thomson TS970 Automatic Transfer Switch

Automatic Transfer Switches

Commercial and industrial contactor-based automatic transfer switch. 100-1200A, open transition, TSC 900 touchscreen controller. UL 1008 / CSA 178 listed.

Overview#

The Thomson TS970 is a contactor-based commercial and industrial automatic transfer switch covering 100A to 1200A. It uses the same TSC 900 controller as the mechanically-held TS870 but with a contactor switching mechanism, providing a more cost-effective option for commercial standby applications that only require open-transition transfer.

The TS970 features electrically and mechanically interlocked switching that prevents simultaneous utility and generator source closure, enclosed power contacts for safe operation and maintenance, and plug-in control devices for field serviceability. The TSC 900 controller provides Modbus communication for building management system integration — a key differentiator from the smaller TS920 which uses the simpler TSC 9 controller.

Contactor vs mechanically-held: the TS970/TS870 decision#

The TS970 and TS870 share the same amperage range (100-1200A) but differ in switching mechanism and controller:

FactorTS970 (Contactor)TS870 (Mech-held)
Transfer speedFaster (~100ms)Slower (~300-500ms)
Closed transitionNoOptional
Idle toleranceCoils may ageMechanical latch holds indefinitely
CostLowerHigher
ControllerTSC 900 (7" touchscreen)TSC 7320 (2.3" LCD)
Max voltage480V600V
Best forFrequent transfers, budget-consciousInfrequent transfers, harsh environments

For the majority of commercial backup installations with standard open-transition requirements, the TS970 is the right choice. Reserve the TS870 for applications that need closed-transition, extremely high inrush tolerance, or environments where the switch may sit idle for months between operations.

Our service experience#

We service Thomson TS970 units in Bay Area commercial and light-industrial facilities. The contactor mechanism provides reliable transfers with fast switching speed, and the TSC 900 controller's Modbus interface integrates cleanly with building management systems — a feature that property managers increasingly require.

The main maintenance item unique to contactor-based ATS units is the holding coil. Unlike mechanically-held switches that latch in position, contactors require continuous coil energization to hold position. Over time (typically 10-15 years), coil insulation can degrade, leading to increased current draw and eventual dropout. We check coil current draw during annual service visits and replace the coil assembly proactively before failure. The plug-in control devices on the TS970 make coil replacement straightforward without requiring a full outage.

Frequently Asked Questions

What is the difference between the Thomson TS870 and TS970?
Both cover 100-1200A but use different switching mechanisms and controllers. The TS870 uses mechanically-held switching with the TSC 7320 controller (2.3-inch LCD), while the TS970 uses contactor switching with the TSC 900 controller (7-inch color touchscreen). The TS870 supports optional closed-transition transfer; the TS970 is open-transition only. The TS870 also supports 600V and bypass-isolation; the TS970 maxes at 480V. The TS970 is the value option for standard commercial backup.
What controller does the TS970 use?
The TS970 uses the TSC 900 microprocessor-based controller with a 7-inch color touchscreen, three-phase voltage monitoring, programmable inputs and outputs, RS232 Modbus RTU communication, and 24VDC control power. The controller handles automatic engine start, open-transition transfer sequencing, in-phase detection, and adjustable neutral position delay.
What amperage ratings are available for the TS970?
The TS970 is available in 100A, 150A, 200A, 250A, 400A, 600A, 800A, 1000A, and 1200A ratings in three-phase configurations. Voltage options include 120/208V, 120/240V, and 277/480V at 50/60 Hz. Both 3-pole and 4-pole configurations are available for 3-wire and 4-wire systems.
Does the TS970 offer closed-transition transfer?
No. The TS970 is open-transition only. For closed-transition capability in the 100-1200A range, specify the Thomson TS870 (mechanically-held). For larger closed-transition requirements, the TS880 covers up to 4000A.
When should I choose the TS970 over the TS920?
The TS920 covers 100-400A with the simpler TSC 9 controller and targets 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, Modbus for BMS integration, or the advanced controller features, specify the TS970.

Service Specifications

ServiceFrequencyNotes
Exercise under loadMonthly (NFPA 110)30+ minutes runtime with load transfer; TSC 900 has built-in exerciser
Connection torque inspectionAnnuallyRetorque all power lugs; thermal cycling loosens connections
Contactor inspectionEvery 3-5 yearsCheck contactor contacts for pitting; verify snap-action and holding coil
Controller firmwareAs releasedTSC 900 firmware updates via USB; check with Thomson for latest revision
Holding coil checkEvery 5 yearsVerify contactor holding coil current draw; replace if degraded to prevent drop-out

Key Terms

Contactor switching
Electromagnetic switching mechanism where contacts are held closed by a continuously energized coil. Faster transfer speed than mechanically-held designs but requires continuous coil power to maintain position.
TSC 900 controller
Thomson's standard controller for the TS880 and TS970, with a 7-inch color touchscreen, front-panel programming with password security, 16 programmable digital inputs, 8 programmable output contacts, RS232 Modbus RTU via GHC, and optional Ethernet Modbus TCP.
In-phase transfer detection
The controller monitors both source waveforms and initiates transfer only when they are electrically in phase, preventing damaging out-of-phase switching events.
Neutral position delay
Adjustable timer that holds the switch in a neutral (both sources disconnected) position during transfer, allowing residual voltage to decay before connecting to the alternate source. Prevents out-of-phase damage.

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