Siemens SENTRON 5SL3120-7 — 1-pole C-curve MCB, 20 A
The Siemens SENTRON 5SL3120-7 is a 1-pole miniature circuit breaker rated 20 A at 230/400 V AC, with a C tripping characteristic. It breaks 4.5 kA per EN 60898 and 5 kA per IEC 60947-2, covering the standard fault-current range for residential and light-commercial distribution boards. Rated operational voltage is 230/400 V AC single/multi-phase, with a maximum of 440 V AC in multi-phase operation and a supply frequency of 50/60 Hz.
Two breaking-capacity ratings are listed: 4.5 kA according to EN 60898 (the standard for household-type MCBs) and 5 kA according to IEC 60947-2 (the industrial standard). The IEC 60947-2 figure governs the part's use in industrial sub-distribution where higher prospective fault currents may be declared on the single-line diagram. Energy limitation class 3 means this MCB limits the let-through energy (I²t) on a downstream fault, which aids selective coordination with upstream devices.
Width is 18 mm (1 modular unit), depth 76 mm, height 90 mm, with an installation depth of 70 mm. Sealable terminals (sealable: Yes) allow the installer to lock the cover after commissioning, preventing tamper.
Thermal derating and ambient limits
At 40 °C it derates to 18.79 A; at 45 °C to 18.4 A; at 55 °C to 16.8 A. This matters when the breaker is ganged in a multi-pole assembly or enclosed in a warm cabinet — the actual continuous current the circuit can carry is the derated figure, not the handle rating.