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RWB/RMW Electronic Overload Relays

  • Solid State overload protection up to 840A / 450kW
  • Wide current settings
  • Adjustable Thermal Class (10, 20 or 30)
  • Self-Supplied
  • Remote Reset

WEG - Solid-State Overload Relays

Solid-State Overload Relays - RWB

rwb Solid-State x Thermal (Bimetallic) Overload Relays
Thermal overload relays are designed to mimic the heat actually generated in the motor. They simulate the motor heating by passing motor current directly or indirectly through bimetal strips. As the motor temperature increases, so does the temperature of the overload relay thermal unit. The heat bends the bimetal strips and, depending on the current setting of the relay, a trip mechanism is activated.
Continuous duty and low number of motor start-ups are common in most usual applications. In such situations, the motor and relay heating curves have a strong relationship. No matter how high the current drawn by the motor, the thermal overload relay provides protection and does not trip unnecessarily.
On the other hand, in applications where frequent motor start-ups (intermittent duty) take place, the increase of heating behaves slightly different in the bimetal strips than in the motor windings and undesired early trippings are common. In such situations, the thermal capacity of the motor is not properly utilized and thermal overload relays are not the most suitable solution.
In solid-state overload relays, the motor current is measured by current transformers and then converted into an electronic signal. Thus, different from thermal overload relays where a significant amount of energy is wasted in the bimetal strips, in solid-state overload relays the low heat losses of the electronic circuits result in less energy consumption and lead to reduced need of ventilation of cabinets.
In addition, due to this technology, the microprocessed signal allows increased precision providing better motor overload protection.
And yet, maybe the most important advantage of solid-state overload relays is the wide current range with the 5:1 ratio between maximum and minimum setting.
When compared to the usual 1.5:1 ratio of the thermal overload relays, this wide range leads to a tremendously reduced number of different items to cover all current ranges up to 840 A.
In a few words, it leads to great reduction in inventory and flexibility on planning.

General Features

The RWE can be directly mounted on WEG contactors (CWB and CWM lines) providing very reliable and flexible motor starter units.
An additional advantage is that the solid-state overload relays RW_E are self-powered, that is, no additional external power is required for operation thus it can be applied directly to the contactor in the same way the thermal overload relays are applied.This feature also allows easy replacement of thermal relays for solid-state ones without the need of rearranging the control circuit wiring or changing the contactor.

WEG RWB-40E and CWB Contactor
WEG RWB-40E and CWB Contactor

Note: overload relays must be protected against short-circuits by fuses or circuit breakers.

WEG RWB Electronic Overload Overview