What this contactor is and what it does
The Siemens 3RT1023-1BB40-ZW98 is a SIRIUS power contactor in the S0 frame, carrying a 24 V DC coil and screw-type terminals for the main current circuit. It switches motor loads up to 5.5 kW at 690 V (AC-3 duty) — that is the rating that governs real motor switching, not the resistive-heater number. The coil pulls 5.4 W on close and holds at 5.4 W DC, so the control transformer sizing is straightforward: one contactor per 24 VDC supply branch, no inrush derating needed. Mounts on a 35 mm DIN rail per DIN EN 50022, screw or snap-on. The 45 mm width and 85 mm height fit the standard S0 panel footprint. Side-by-side mounting is allowed with 6 mm clearance at the side — no gap between contactors if the ambient stays within the -25 to +60 °C operating range. Pollution degree 3 means it is rated for industrial environments with conductive contamination; the IP20 front keeps fingers out, but the terminals are IP00 — wire into a live panel with the cover on.
Ratings that decide the fit
The AC-3 motor-switching rating is the one that matters for a pump, fan, or compressor: 4.5 kW at 500 V and 5.5 kW at 690 V. AC-4 at 400 V is 8.5 A — that covers reversing or inching duty where the contactor makes and breaks stalled-rotor current. AC-2 at 400 V is 4 kW, for slip-ring motor starting. The AC-12 maximum operating current is 10 A, for resistive loads like heater banks. The coil switching capacity at 24 V is 10 A; at 60 V it drops to 2 A, at 110 V to 1 A, and at 220 V to 0.3 A — that is the auxiliary contact rating, not the main poles. Short-circuit coordination: with type 2 assignment (no welding after a fault), use a 25 A gL/gG fuse upstream. With type 1 coordination (welding allowed, no fire or shock), a 63 A gL/gG fuse works. The mechanical life is 10 million operations — typical for a contactor in this frame size, but the electrical life at full AC-3 load will be lower; the datasheet curve governs that.
Terminal and wiring detail
Main circuit screw terminals accept 2x (0.5 to 1.5 mm²) solid, 2x (0.75 to 2.5 mm²) solid, or max 2x (0.75 to 4 mm²) solid. Stranded: 2x (1 to 2.5 mm²), 2x (2.5 to 6 mm²), or max 2x 10 mm². AWG equivalents: 2x (16 to 12), 2x (14 to 10), 1x 8. The depth is 101 mm — verify clearance to the back panel or enclosure door, especially with aux blocks or suppressor modules added on the front.