The Siemens 6EP1961-3BA21 is a DC buffer module that bridges short mains interruptions for 24 V DC loads. It delivers up to 40 A aggregate current from a 24 to 28.8 V DC input, with the output voltage following the input minus roughly 0.5 V. The controlled, isolated DC output is backed by a relay contact (changeover, rated 8 A at 240 V AC or 24 V DC) that signals OK when both input voltages stay above an adjustable threshold of 20 to 25 V. At 96.6% efficiency, the module wastes little heat in the cabinet — important when the 70 × 125 × 120 mm enclosure relies on natural convection over the -25 to +60 °C operating range. Above +60 °C, derate the 40 A aggregate by 3% per Kelvin up to +70 °C.
Snaps onto DIN rail EN 60715 35×7.5/15. The 70 mm width occupies three standard 22.5 mm module positions. Allow 50 mm clearance above and below for convection airflow and wiring access — the top and bottom clearance figures are 50 mm each, with 0 mm left and right clearance needed. Input, output, and ground terminate via one screw terminal each accepting 0.33 to 10 mm² single-core or finely stranded wire. Protection class is IP20 — suitable for dry, enclosed control cabinets only.
Carries CE, cULus-Listed (UL 508, CSA C22.2 No. 107.1, File E197259), EAC, and shipbuilding approvals from ABS and DNV GL. Galvanic isolation is SELV per EN 60950-1. Conducted and radiated emissions meet EN 55022 Class B; immunity complies with EN 61000-6-2. Not ATEX, IECEx, or FM registered, and not NEC Class 2.
Reliability and storage
MTBF at 40 °C is 6,471,654 hours — roughly 739 years continuous, a figure that reflects the semiconductor-grade design. Storage and transport range is -40 to +85 °C. Specifications are stated at rated input voltage and +25 °C ambient unless otherwise noted.