SIRIUS 3RB20/3RB21 Solid-State Overload Relays

(1)   Connection for mounting onto contactors:

Optimally adapted in electrical, mechanical and design terms to the contactors and soft starters, these connecting pins can be used for direct mounting of the overload relays. Stand-alone installation is possible as an alternative (in some cases in conjunction with a standalone installation module).

(2)   Selector switch for manual/automatic RESET and RESET button:

With the slide switch you can choose between manual and automatic RESET. A device set to manual RESET can be reset locally by pressing the RESET button. On the 3RB21 a solid-state remote RESET is integrated.

(3)   Switch position indicator and TEST function of the wiring:

Indicates a trip and enables the wiring test.

(4)   Solid-state test:

Enables a test of all important device components and functions

(5)   Motor current setting:

Setting the device to the rated motor current is easy with the large rotary knob.

(6)   Trip class setting/internal ground-fault detection (only 3RB21):

Using the rotary switch you can set the required trip class and activate the internal ground-fault detection dependent on the starting conditions.

(7)   Connecting terminals (removable terminal block for auxiliary circuits):

The generously sized terminals permit connection of two conductors with different cross-sections for the main and auxiliary circuits. The auxiliary circuit can be connected with screw-type terminals and alternatively with spring-loaded terminals.

The 3RB20 and 3RB21 solid-state overload relays up to 630 A with internal power supply have been designed for current dependent protection of loads with normal and heavy starting against excessive temperature rises due to overload, phase unbalance or phase failure. An overload, phase unbalance or phase failure result in an increase of the motor current beyond the set motor rated current. This current rise is detected by the current transformers integrated into the devices and evaluated by corresponding solid-state circuits which then output a pulse to the auxiliary contacts. The auxiliary contacts then switch off the load by means of a contactor. The break time depends on the ratio between the tripping current and set current I_e and is stored in the form of a long-term stable tripping characteristic.

In addition to current-dependent protection of loads against excessive temperature rises due to overload, phase unbalance and phase failure, the 3RB21 solid-state overload relays also allow internal ground-fault detection (not possible in conjunction with wye-delta assemblies). This provides protection of loads against high-resistance short-circuits due to damage to the insulation material, moisture, condensed water etc.

The "tripped" status is signaled by means of a switch position indicator. Resetting takes place either manually or automatically after the recovery time has elapsed.

The devices are manufactured in accordance with environmental guidelines and contain environmentally friendly and reusable materials. They comply with all important worldwide standards and approvals.

The most important features and benefits of the 3RB20/3RB21 solid-state overload relays are listed in the overview table.

The 3RB20/3RB21 solid-state overload relays are suitable for customers from all industries who want to guarantee optimum inverse-time delayed protection of their electrical loads (e.g. motors) under normal and heavy starting conditions (CLASS 5 to CLASS 30), minimize project completion times, inventories and power consumption, and optimize plant availability and maintenance management.

The 3RB20/3RB21 solid-state overload relays have been designed for the protection of three-phase motors in sinusoidal 50/60 Hz voltage networks. The relays are not suitable for the protection of single-phase AC or DC loads. The 3RU11 thermal overload relay or the 3RB22/3RB23 solid state overload relay can be used for single-phase AC loads. For DC loads we recommend the 3RU11 thermal overload relay.

The devices are insensitive to external influences such as shocks, corrosive environments, ageing and temperature changes. For the temperature range from –25 C to +60 °C, the 3RB20/3RB21 solid-state overload relays compensate the temperature according to IEC 60947-4-1. Configuration notes for use of the devices below –25 °C or above +60 °C on request.

The 3RB20/3RB21 solid-state overload relays are suitable for the overload protection of explosion-proof motors with "increased safety" type of protection EEx e. The relays meet the requirements of EN 60079-7 (Electrical apparatus for potentially explosive atmospheres – Increased safety "e"). The basic safety and health requirements of ATEX guideline 94/9/EG are fulfilled by compliance with

•        EN 60947-1

•        EN 60947-4-1

•        EN 60947-5-1

•        EN 60079-14

EU type test certificate for Group II, Category (2) G/D under application, number on request.

The following accessories are available for the 3RB20/3RB21 solid-state overload relays:

•        One terminal bracket each for the overload relays size S00 and S0 (sizes S2 to S12 can be installed as single units without a terminal bracket)

•        One mechanical remote RESET module for all sizes

•        One cable release for resetting devices which are difficult to access (for all sizes)

•        One sealable cover for all sizes

•        Box terminals for sizes S6 and S10/S12

•        Terminal covers for sizes S2 to S10/S12