Siemens 3UG4511-1AP20 Phase Sequence Monitor

Siemens 3UG4511-1AP20 Phase Sequence Monitor is a compact analog monitoring relay that ensures three‑phase power is connected in the correct order before energizing equipment, helping prevent motor damage from phase reversal or loss. It senses three‑phase voltages across 320–500 V AC at 50/60 Hz and provides a single changeover contact (SPDT) for signaling or interlocking, with screw terminals for secure wiring. This phase sequence monitor is intended for use with equipment such as motors, compressors, and pumps in industrial control panels where correct phase sequence and reliable startup are critical. Siemens lists a preferred successor, 3UG5511-1AR20, which covers the same 3 x 320–500 V, 50–60 Hz range and 1 changeover contact; the 3UG4511‑1AP20 variant is considered an older model in the line.