What the 800 V / 8 A rating means on the board
The STMicroelectronics T835T-8G is an 800 V off-state, 8 A RMS on-state Alternistor triac in the Snubberless™ series, housed in a D²PAK surface-mount package. It is designed for AC load switching where inductive kickback would otherwise demand an external RC snubber — the device's internal structure commutates cleanly without one for many motor, valve, and transformer loads. The 800 V blocking rating covers 240 VAC mains with healthy margin and handles 480 VAC line-to-line in three-phase systems. The 8 A continuous rating suits resistive heaters, small motors, and lighting banks up to about 2 kW on 240 VAC.
Snubberless™ — what it saves on the BOM
The Alternistor – Snubberless construction means the triac can switch inductive loads without the usual RC snubber network across the main terminals. That eliminates a resistor and a capacitor per phase — roughly $0.10–0.20 BOM savings per device, plus the board area and assembly cost. The trade-off is a higher gate trigger current (35 mA max) and hold current (40 mA max) compared to a standard triac, so the gate drive needs to source that current reliably. For a microcontroller-driven optocoupler or pulse transformer, check that the drive circuit can deliver the 35 mA Igt peak at the 1.3 V Vgt threshold.
For 8 A RMS continuous, a 1 oz copper pad of at least 6 cm² is typical to keep junction temperature under 125 °C in a 50 °C ambient.