The Siemens SENTRON 4AC3740-0 is a 40 VA continuous-duty safety transformer providing the two most widely used SELV control voltages — 12 V and 24 V AC — from a single compact unit. It powers switching relays, Insta contactors, and building automation control circuits at the 40 VA level, which covers the majority of multi-relay control panel loads. Compared to the 4AC3724-0 (24 VA), this model delivers nearly double the power in the same 3-module width. Insulation class F construction ensures reliable long-term thermal performance in continuously energized installations.

Key Features

• 40 VA continuous-duty — powers larger relay banks and contactor groups
• Selectable 12 V / 24 V AC output — covers both common SELV control standards
• Insulation class F — enhanced thermal endurance for 24/7 operation
• Built-in PTC auto-reset protection — no maintenance or fuse changes
• Safety class II, 4 kV isolation, EN 61558-2-6 certified
• 3-module (54 mm) DIN rail — space-efficient for the power rating

Technical Data

Applications

Building automation and control panels: lighting contactor circuits, heating zone valve control, HVAC relay logic, stairwell timer installations, and apartment block intercom/access control. The 12 V/24 V selectable output covers both legacy 12 V relay systems and modern 24 V building automation standards.