The Schneider Electric A9N21376 is a DT40N miniature circuit breaker (MCB) from the DT40 series, configured as 1P+N with a 16 A rated current and a D tripping curve. This is a single-module (1P+N) unit that switches the phase and provides a switched neutral, common in single-phase final subcircuits where disconnecting the neutral is required by local wiring rules.
What the D curve means for the panel
In a typical industrial or commercial panel, it feeds a motor starter, a small compressor, or a bank of discharge lighting. The D curve's magnetic trip at 10–20× In (160–320 A) clears a hard short without opening on the motor's starting surge, which can pull 6–8× FLA for a few cycles. Coordination with an upstream S-curve or B-curve MCB is straightforward because the D curve's lower instantaneous threshold is higher — selectivity holds for most fault levels below the upstream breaker's magnetic pickup.