The IRH, IRV, ULH, and ULV are the flagship standard wire wound metal clad resistor series from RMS — a comprehensive family spanning 60W to 500W that covers the full breadth of industrial motor control, power electronics, and electric vehicle charging applications. The four model designations reflect two key variables: mounting orientation and certification level. IRH (Horizontal) and IRV (Vertical) are the standard series; ULH and ULV are their UL-approved equivalents, sharing identical dimensions and electrical characteristics while additionally carrying UL and CE certification for installations where regulatory compliance is mandatory.
All four series share the same extruded aluminium housing, which provides robust mechanical protection and functions as an integrated heatsink when the resistor is bolted to a chassis surface. For the higher power models (150W, 300W, 400W, and 500W), a mid-point bracket is recommended to ensure full and even contact with the heatsink surface — critical for achieving the rated power dissipation under sustained load conditions. The IP65 enclosure rating protects against dust ingress and water jets, making these resistors well-suited to outdoor, underhood, and industrial panel environments.
Termination options cover both flying leads and tab terminals, with inductive and non-inductive winding configurations available across the entire range. The non-inductive option is essential for snubber and high-frequency switching applications where residual winding inductance would degrade transient suppression performance. Flying lead specifications are matched to the power and resistance range of each model, with options including standard wire, UL3512 AWG10, and UL3512 AWG14 cables — the UL-rated wire being mandatory for ULH/ULV variants. Thermostat options (internal and discrete connection) are also available across the range on request.
The resistance range spans 0.1Ω to 6.8kΩ depending on model and winding type, with an extended ohmic range of 1mΩ to 750kΩ available on request for specialist applications. Tolerance options from ±0.5% to ±10% accommodate precision discharge specifications through to general industrial current-limiting requirements. The wide operating temperature range of –55°C to +200°C, combined with a TCR of ±260 ppm/°C maximum, ensures stable, predictable performance across the full range of ambient conditions encountered in motor drives, EV systems, and outdoor power equipment.
Characterisation testing confirms reliable performance across short-time overload (5× rated power for 60W; 10× rated power for 80W–500W, both for 5 seconds), moisture resistance (40°C / 95% RH for 500 hours), thermal shock, vibration (10Hz–55Hz, 2 hours per axis), moisture load life, and extended full-power load life — meeting the demands of continuous industrial duty cycles.
