Overload Relays 3RU1 Thermal Overload Relays 3RU11 for standard applications Function Basic functions The 3RU11 thermal overload relays are designed for: Inverse-time delayed protection of loads from overloading Inverse-time delayed protection of loads from phase failure Recovery time After tripping due to overload, the 3RU11 thermal overload re- lays require some time until the bimetal strips have cooled down. The device can only be reset after the bimetal strips have cooled down. This time (recovery time) depends on the tripping cha- racteristics and strength of the tripping current.
Control circuit The 3RU11 thermal overload relays do not require an additional supply voltage for operation. The recovery time allows the load to cool down after tripping due to overload. Short-circuit protection TEST function Fuses or motor starter protectors must be used for short-circuit protection. The TEST slide can be used to check whether the operational 3RU11 thermal overload relay is working properly. Actuating the slide simulates tripping of the relay. During this simulation the NC contact (95-96) is opened and the NO contact (97-98) is closed. This tests whether the auxiliary circuit has been correctly con- nected to the overload relay.
If the 3RU11 thermal overload relay has been set to automatic RESET, the overload relay is automa- tically reset when the TEST slide is released. The relay must be reset with the RESET button if it has been set to manual RESET. For assignments of the corresponding short-circuit protection devices to the 3RU11 thermal overload relays with/without con- tactor see "Technical specifications" and Catalog LV 1, "Selec- tion and ordering data" . Trip classes The 3RU11 thermal overload relays are available for normal star- ting conditions with trip class CLASS 10. For heavy starting con- ditions see 3RB2 solid-state overload relays.
STOP function If the STOP button is pressed, the NC contact is opened. This switches off the contactor downstream and thus the load. The load is switched on again when the STOP button is released. For details of the trip classes see "Characteristic Curves" . Phase failure protection The 3RU11 thermal overload relays are fitted with phase failure sensitivity (see "Characteristic Curves") in order to minimize tem- perature rises of the load in the case of a phase failure during single-phase operation.
Display of the operating state The respective operating state of the 3RU11 thermal overload relay is displayed by means of the position of the marking on the TEST function/switch position indicator slide. After tripping due to overload or phase failure, the marking on the slide is to left on the "O" mark, otherwise it is on the "I" mark. Setting The 3RU11 thermal overload relays are set to the rated motor current by means of a rotary knob. The scale of the rotary knob is shown in ampere. Auxiliary contacts Manual and automatic reset The 3RU11 thermal overload relays are fitted with an NO contact for the tripped signal, and an NC contact for disconnecting the contactor.
Automatic and manual reset is selected by pressing and turning the blue button (RESET button). If the button is set to manual re- set, the overload relay can be reset directly by pressing the RESET button. Resetting is possible in combination with mecha- nical and electrical reset options from the range of accessories (see Catalog LV 1, "Accessories") . If the blue button is set to au- tomatic RESET, the relay is reset automatically. The time between tripping and resetting is determined by the re- covery time. 9 Siemens · 2009