SIRIUS S0 power contactor — 4 NO, 7.5 kW AC-2, 24 V coil
The Siemens 3RT1325-1AC20 is a SIRIUS S0-frame power contactor with four normally-open main contacts, rated for 7.5 kW at 400 V in AC-2 duty (slip-ring motor starting). The coil is 24 V, rated for both 50 Hz and 60 Hz operation. Screw-type terminals on the main circuit; auxiliary circuits accept solid or stranded wire from 0.5 to 4 mm². Mounts via screw or snap-on onto 35 mm DIN rail per EN 50022 — standard panel integration.
Key ratings and what they mean for fit
The 7.5 kW AC-2 rating at 400 V governs motor switching for slip-ring or wound-rotor motors — the contactor is sized for that load, not for higher AC-3 or AC-4 duty. The 4 NO main contact configuration means it switches four independent power paths, typical for star-delta or reversing starters where multiple poles are needed. Operating temperature range is -25 to +60 °C, with pollution degree 3 (conductive pollution, typical in industrial enclosures). Side-by-side mounting is permitted with 6 mm spacing to the side — no derating penalty when ganged. Auxiliary contact ratings span the control voltage range: 10 A at 24 V, 6 A at 230 V, 3 A at 400 V, and 0.3 A at 220 V DC. These are the switching limits for the coil or signal circuits this contactor controls — useful when sizing downstream pilot devices or PLC outputs.
Wiring and coordination
Main circuit terminals accept 2x (1–2.5 mm²) or 2x (2.5–6 mm²) solid/stranded, up to 2x 10 mm² maximum. Auxiliary terminals take 2x (0.5–1.5 mm²) or 2x (0.75–2.5 mm²), max 2x 4 mm². For Type 2 coordination (no damage to contactor on short circuit), use a gL/gG fuse rated 25 A; for Type 1 coordination (contactor may need replacement), a 63 A fuse is permitted. The IP20 front and IP00 terminal protection is standard for enclosed panels — not rated for washdown.