Overload Relays 3RU1 Thermal Overload Relays 3RU11 for standard applications Overview "Increased safety" type of protection EEx e acc. to ATEX di- rective 94/9/EC The 3RU11 thermal overload relays are suitable for the overload protection of explosion-proof motors with "increased safety" type of protection EEx e; see Catalog LV 1, Chapter 20 "Appendix" --> "Standards and ap- provals" --> "Type overview of approved devices for explosion- protected areas (ATEX Explosion Protection)". 1 2 3 EC type test certificate for Category (2) G/D exists. It has the num- ber DMT 98 ATEX G 001. 5 4 7 6 Design Device concept The 3RU11 thermal overload relays are compact devices, i. e.
current measurement and the evaluation unit are integrated in a single enclosure. (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 di- rect mounting of the overload relays. Stand-alone installation is possible as an alternative (in some cases in conjunction with a stand-alone instal- lation module). (2)Selector switch for manual/automatic RESET and RESET button: With this switch you can choose between manual and automatic RESET. A device set to manual RESET can be reset locally by pressing the RESET button.
A remote RESET is possible using the RESET mod- ules (accessories), which are independent of size. (3)Switch position indicator and TEST function of the wiring: Indicates a trip and enables the wiring test. (4)Motor current setting: Setting the device to the rated motor current is easy with the large rotary knob. (5)STOP button: If the STOP button is pressed, the NC contact is opened. This switches off the contactor downstream. The NC contact is closed again when the button is released. (6)Transparent sealable cover Secures the motor current setting and the TEST function against adjustment. (7)Supply terminals:
The generously sized terminals permit connection of two conductors with different cross-sections for the main and auxiliary circuits. The aux- iliary circuit can be connected with screw terminals and alternatively with spring-type terminals. Mounting options The 3RU11 thermal overload relays can be mounted directly onto the 3RT1 contactors (exception: size S00 with Cage Clamp termi- nals can only be installed as a stand-alone installation). With the matching terminal brackets the devices can still be installed as stand-alone units. For more information on the mounting options see "Technical spe- cifications" and Catalog LV 1, "Selection and ordering data" .
Connection methods All sizes of the 3RU11 thermal overload relays with screw terminal can be connected to the auxiliary and main current paths. Rails can be connected to the main conductor connections of size S3 overload relays if the box terminals are removed. As an alternative, the devices are also available with Cage Clamp terminals. The auxiliary conductor connections of these devices, and for size S00 the main conductor connections as well, are fitted with Cage Clamp terminals. For more information on the connection options see "Technical specifications" and Catalog LV 1, "Selection and ordering data".
Overload relays in contactor assemblies for wye-delta starting When overload relays are used in combination with contactor as- semblies for wye-delta starting it must be noted that only 0.58 times the motor current flows through the line contactor. An over- load relay mounted onto the line contactor must be set to 0.58 times the motor current. The 3RU11 thermal overload relays up to 100 A have been desi- gned for inverse-time delayed protection of loads with normal starting (see "Function") against excessive temperature rises due to overload or phase failure. An overload or phase failure results in an increase of the motor current beyond the set rated motor cur- rent.
Via heating elements, this current rise heats up the bimetal strips inside the device which then bend and as a result trigger the auxiliary contacts by means of a tripping mechanism. The auxili- ary contacts then switch off the load by means of a contactor. The break time depends on the ratio between the tripping current and current setting I e and is stored in the form of a long-term stable tripping characteristic (see "Characteristic Curves") . An assignment of the 3RU11 thermal overload relays to the line contactors of our 3RA contactor assemblies for wye-delta starting can be found in Chapter 3 "Controls: Contactors and Contactor Assemblies" .
Operation with frequency converter The 3RU11 thermal overload relays are suitable for operation with frequency converters. Depending on the frequency of the conver- ter, a higher current than the motor current must be used in some cases due to eddy-currents and skin effects. The "tripped" status is signaled by means of a switch position in- dicator. Resetting takes place either manually or automatically af- ter the recovery time has elapsed (see "Function") . The devices are manufactured in accordance with environmental guidelines and contain environmentally friendly and reusable ma- terials. They comply with all important worldwide standards and approvals. 8 Siemens · 2009