What the adjustable hysteresis and time delay mean for your protection scheme
The RM4UA33M is a voltage measurement relay from the Harmony RM4U series, designed for overvoltage or undervoltage detection per EN/IEC 60255-6. Its adjustable hysteresis of 5 to 30 % of the set threshold prevents nuisance cycling when the monitored voltage hovers near the trip point — set it wide enough to ride through normal line fluctuations but tight enough to catch a sustained deviation. The adjustable time delay, 0.05 to 30 s, lets you coordinate with downstream protection devices. A short delay (0.05 s) catches fast overvoltage events; a longer delay (several seconds) avoids tripping on temporary sags during motor starting or transformer inrush. Two C/O (changeover) output contacts give you independent signalling paths — one for an alarm, one for a trip circuit, for example. The contacts are rated for a minimum switching capacity of 10 mA at 12 V, so they can drive PLC inputs directly without a wetting-current issue.
Panel fit and environmental ratings
The relay occupies 22.5 mm (0.9 in) on a DIN rail — two and a half 9 mm pitches — and is 80 mm deep. That 22.5 mm width is the standard single-module footprint for industrial control relays, so it fits any populated rail without crowding. IP20 on the terminals (finger-safe) and IP50 on the casing means it is suitable for clean, dry indoor panels. Pollution degree 3 per IEC 60664-1 allows operation in environments with conductive pollution, typical of many industrial control cabinets. The relay withstands 15 gn shock for 11 ms and vibration of 0.35 mm at 10-55 Hz per IEC 60068-2-6, so it holds calibration in applications near rotating machinery or conveyors.
Compliance and documentation
The RM4UA33M is designed to EN/IEC 60255-6 (measuring relays and protection equipment) and carries CE marking under the EMC Directive 89/336/EEC and Low Voltage Directive 73/23/EEC. Dielectric test voltage is 2.5 kV, and it withstands a 4.8 kV non-dissipating shock wave. Electromagnetic compatibility is verified to IEC 61000-4-2 (6 kV contact / 8 kV air discharge, level 3) and IEC 61000-4-4 (2 kV fast transients, level 3). Conducted and radiated emissions meet CISPR 11 Group 1 Class A and CISPR 22 Class A.