40 A D-curve MCB for industrial feeder and motor circuits
The Siemens 5SY7240-8CC is a SENTRON miniature circuit breaker (MCB) with a 40 A rated current, D tripping characteristic, and 2-pole construction for 400 V AC circuits. The D-curve means it tolerates high inrush currents — typically 10 to 20 times the rated current for short durations — making it a fit for motor starters, transformers, and welding equipment where the startup surge would nuisance-trip a B or C curve. Its 15 kA breaking capacity per IEC 60947-2 (at 400 V AC) handles substantial fault currents upstream in an industrial panel; the 5 kA rating per UL 1077 and CSA C22.2 No. 235 covers North American installations.
Panel integration and wiring
Snaps onto DIN rail via the quick-assembly system, occupying 2 width units (36 mm wide). Overall depth is 76 mm with an installation depth of 70 mm — leaves clearance behind the DIN rail for wiring. Terminal capacity accepts solid or stranded conductors from 0.75 mm² up to 35 mm², with a tightening torque range of 2.5 to 3.5 N·m; that covers most panel feed conductors up to a 4 AWG equivalent. Both top and bottom terminals are combined (line/load reversible), and the unit is sealable for tamper-proofing in metering or critical circuits.