What it is and what it does
The Siemens 3RT1015-1BB42-ZW98 is a SIRIUS power contactor in the S00 frame size, built for switching motor loads and resistive loads in control panels. The 24 VDC coil pulls in at 0.85 x rated voltage and drops out at 1.1 x rated voltage, so it holds reliably on a 24 V supply but releases cleanly when the control signal goes high — that 1.1 dropout factor means it won't chatter on a floating ground. Rated for 4 kW at 690 V AC-3 duty, it handles a 3-phase motor up to that power level; the AC-4 rating at 400 V is 6.5 A, which covers reversing or inching applications where the contactor makes and breaks the load under full current. The screw-type main terminals accept 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or max 2x (0.75 to 4 mm²) — solid or stranded — and the AWG equivalent is 2x (20 to 16), 2x (18 to 14), or 1x 12. That covers most panel wiring up to 4 mm² without needing ferrules, though for stranded wire a ferrule keeps the strands together under the screw. The coil draws 3.3 W closing and 3.3 W holding DC, so the power supply needs to deliver that continuously; no surge at pickup beyond the steady-state draw.
Mounting and integration
Mounts via screw or snap-on onto a 35 mm DIN rail per EN 50022. The 45 mm width and 57.5 mm height fit the standard S00 footprint; depth is 72 mm, which leaves room for wiring in a 200 mm deep enclosure. Side-by-side mounting is allowed with 6 mm spacing between units — no derating needed for heat buildup when ganged. Pollution degree 3 means it's rated for industrial environments with conductive dust or occasional condensation, so it's fine in an unsealed panel as long as the front IP20 keeps fingers out.
Coordination and protection
For Type 2 coordination (no damage to the contactor after a short circuit), the required upstream fuse is gL/gG 20 A. For Type 1 coordination (contactor may need replacement after a fault), the fuse can be 35 A gL/gG. The AC-12 resistive rating is 10 A, which covers heater or lighting loads where the contactor switches steady-state current without motor inrush. Mechanical life is 30 million operating cycles, so for a line cycling once every 10 seconds that's about 9.5 years of continuous service before the contacts wear out.