The STMicroelectronics T2535T-8T is a standard triac in the ECOPACK®2 series, rated for 25 A RMS on-state current and 800 V off-state voltage. It comes in a TO-220-3 through-hole package with a single triac configuration.
25 A RMS and 800 V — the load and margin decision
The 25 A RMS on-state current is the continuous load rating. For a resistive heater or a motor drive running at 25 A RMS, this triac is sized correctly with no derating margin at full load — you will want to heatsink it properly. The 800 V off-state voltage covers 480 VAC line-to-line applications with margin, though the typical use case is 230/277 VAC where the 800 V rating absorbs the 600 V+ repetitive peak voltage seen on a noisy mains line. The non-repetitive surge current rating of 200 A at 50 Hz and 210 A at 60 Hz is the figure to check against your inrush. A 25 A resistive load has a cold-start inrush maybe 1.5x steady-state, so this is comfortable. But a bank of discharge lamps or a motor starting under load can pull 8-10x rated current for a few cycles — verify your worst-case surge stays under these numbers. The 35 mA gate trigger current and 1 V gate trigger voltage are standard sensitivity levels compatible with most optocoupler or microcontroller-driven gate drive circuits. The 35 mA holding current means the triac will stay latched once triggered as long as the load current stays above that threshold — fine for most loads, but a very light load (below 35 mA) may drop out at the zero-cross.
Package and mounting — TO-220-3 through-hole
The TO-220-3 through-hole package with the supplier device package listed as TO-220 is the standard three-lead power package. The tab is the main terminal (MT2) and is electrically live — you need an insulating pad and washer if mounting to a grounded heatsink. The package is rated for the full 25 A RMS, but thermal management is on you: the junction-to-case thermal impedance determines the heatsink size needed to stay below 150°C junction at full load. The through-hole mounting is straightforward for wave-solder or hand-solder assembly.