Thomson Power Systems · TS840 Series (Agriculture/Light Industrial)

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Thomson TS840 Automatic Transfer Switch

Automatic Transfer Switches

Agriculture and light-industrial automatic transfer switch. 100-800A, open transition, mechanically interlocked switching, TSC 80 controller. UL 1008 listed.

Overview#

The Thomson TS840 is a mechanically-interlocked automatic transfer switch built for agriculture, telecom, and light-industrial standby power applications. Available from 100A to 800A in single-phase and three-phase configurations, it uses a heavy-duty brushless gear-motor mechanism with fully enclosed silver alloy contacts rated for 3-cycle short circuit withstand at 65,000A (240V) with circuit breaker protection, or 100,000A with fuse protection.

The TS840 ships standard in a NEMA 3R outdoor enclosure, making it suitable for exposed installations common in agricultural and telecom site deployments. The TSC 80 microprocessor controller handles all automatic transfer functions including engine start signaling, voltage and frequency monitoring, and programmable time delays. A service-entrance rated (SE) variant is available for installations requiring the ATS to serve as the main disconnect. The operating temperature range spans -40°C to 50°C.

Where the TS840 fits#

The TS840 occupies the entry tier of Thomson's mechanically-held ATS lineup, positioned below the TS870 (commercial/industrial) and TS880 (mission critical). Its defining characteristics:

Typical installations: agricultural irrigation pumps, dairy/poultry operations, cell towers, rural telecom huts, and small industrial buildings without critical-continuity requirements.

Our service experience#

In Northern California agriculture and telecom, we see the TS840 most commonly in the 200-400A range on dairy operations and cell tower sites. The mechanically-held mechanism is well-suited to infrequent transfers — these units might only operate a few times per year during grid outages, and the gear-motor mechanism tolerates long idle periods better than contactors that can develop coil issues from disuse.

Common service items: the NEMA 3R enclosure holds up well outdoors, but we recommend annual inspection of the door gaskets and conduit entry points for moisture intrusion, particularly in Central Valley agricultural environments where dust and irrigation spray create accelerated corrosion conditions. The TSC 80 controller is straightforward to program in the field; the optional SDM LCD display module makes timer adjustments easier than the base LED interface.

Frequently Asked Questions

What applications is the Thomson TS840 designed for?
The TS840 is specifically designed for agriculture, telecommunications, and light-industrial standby applications. It uses a heavy-duty brushless gear-motor mechanism with mechanical interlocking between utility and generator switching units, providing reliable open-transition transfer in environments where simplicity and durability are priorities. The standard NEMA 3R outdoor enclosure makes it suitable for exposed installations without additional weather protection.
What amperage ratings are available for the TS840?
The TS840 is available in 100A, 150A, 200A, 250A, 400A, 600A, and 800A ratings. Single-phase units (2-pole) are available at 120/240V, while three-phase units (3-pole) support 120/208V and 120/240V systems. All ratings carry 100% continuous current capacity for all load types. A service-entrance rated (SE) variant is also available.
What controller does the TS840 use?
The TS840 uses the TSC 80 microprocessor-based controller for voltage sensing, frequency monitoring, and timing functions. It includes programmable timers for engine start delay (0-60 sec), engine warm-up, cool-down (0-30 min), neutral position delay (0-60 sec), and utility return (0-30 min), plus a fixed 30-minute exercise timer. An optional SDM LCD display module is available for field adjustments.
What are the short circuit withstand ratings?
The TS840 is rated for 3-cycle short circuit current withstand. At 240V, the withstand rating is 65,000A with upstream circuit breaker protection. With upstream fuse protection (Type T or J), the rating increases to 100,000A for the 100-600A frames. The 800A frame fuse rating requires factory consultation.
How does the TS840 compare to the TS870?
The TS840 is Thomson's entry-level mechanically-held ATS for simpler applications, while the TS870 is the commercial/industrial workhorse. Key differences: the TS840 tops out at 800A while the TS870 goes to 1200A; the TS840 is open-transition only while the TS870 offers optional closed-transition and bypass-isolation; the TS840 uses the simpler TSC 80 controller while the TS870 uses the advanced TSC 7320 with LCD display and Modbus; and the TS840 ships in NEMA 3R outdoor enclosure by default while the TS870 defaults to NEMA 1 indoor.
What are the physical dimensions?
Dimensions vary by frame (NEMA 3R enclosure): 100-200A is 31.1 x 22.3 x 14 inches (143 lbs); 250A is 35.1 x 27.3 x 14 inches (172 lbs); 400A is 43.1 x 34.3 x 13 inches (227 lbs); 600A is 46.1 x 36.3 x 14.5 inches (248 lbs); 800A is 48.1 x 37.8 x 18 inches (309 lbs). Distribution breaker variants are larger.

Service Specifications

ServiceFrequencyNotes
Exercise under loadMonthly (NFPA 110)Fixed 30-minute exercise cycle; on-load or off-load programmable
Connection torque inspectionAnnuallyRetorque all power lugs per Thomson spec; thermal cycling loosens connections
Contact inspectionEvery 5 years or 1,000 operationsInspect silver alloy contacts for pitting or erosion; replace as a set
Gear-motor mechanismEvery 5 yearsInspect brushless gear-motor for wear; verify full travel on both sources

Key Terms

Open-transition transfer
A brief (typically 100-500ms) interruption between disconnecting from one source and connecting to the other. Standard for agricultural and light-industrial backup where momentary outage is acceptable.
Mechanically-held switching
Switch positions are maintained by a mechanical latch mechanism driven by a brushless gear-motor, as opposed to contactor-style switches held by an electromagnetic coil. More robust for infrequent operations and harsh environments.
NEMA 3R enclosure
Outdoor-rated enclosure providing protection against rain, sleet, and external ice formation. Standard on the TS840 for agricultural and outdoor telecom installations.
TSC 80 controller
Thomson's basic microprocessor-based ATS controller with status LEDs, programmable timers, exercise scheduling, and an isolation plug for disconnecting control circuits. Optional SDM LCD display module available for field adjustments.

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