Advertisement
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
Control circuit
The 3RU11 thermal overload relays do not require an additional
supply voltage for operation.
Short-circuit protection
Fuses or motor starter protectors must be used for short-circuit
protection.
For assignments of the corresponding short-circuit protection de-
vices to the 3RU11 thermal overload relays with/without contactor
see "Technical specifications" and Catalog LV 1, "Selection and or-
dering
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.
For details of the trip classes see "Characteristic
Phase failure protection
The 3RU11 thermal overload relays are fitted with phase failure
sensitivity
(see "Characteristic Curves")
perature rises of the load in the case of a phase failure during sin-
gle-phase operation.
Setting
The 3RU11 thermal overload relays are set to the rated motor cur-
rent by means of a rotary knob. The scale of the rotary knob is
shown in ampere.
Manual and automatic reset
Automatic and manual reset is selected by pressing and turning
the blue button (RESET button). If the button is set to manual reset,
the overload relay can be reset directly by pressing the
RESET button. Resetting is possible in combination with mechani-
cal and electrical reset options from the range of accessories
Catalog LV 1,
"Accessories"). If the blue button is set to automatic
RESET, the relay is reset automatically.
The time between tripping and resetting is determined by the re-
covery time.
8
Siemens · 2011
Recovery time
After tripping due to overload, the 3RU11 thermal overload relays
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 charac-
teristics and strength of the tripping current.
The recovery time allows the load to cool down after tripping due
to overload.
TEST function
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 connec-
ted to the overload relay. If the 3RU11 thermal overload relay has
been set to automatic RESET, the overload relay is automatically
reset when the TEST slide is released. The relay must be reset with
the RESET button if it has been set to manual RESET.
STOP function
If the STOP button is pressed, the NC contact is opened. This swit-
ches off the contactor downstream and thus the load. The load is
Curves".
switched on again when the STOP button is released.
Display of the operating state
The respective operating state of the 3RU11 thermal overload re-
in order to minimize tem-
lay 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.
Auxiliary contacts
The 3RU11 thermal overload relays are fitted with an NO contact
for the tripped signal, and an NC contact for disconnecting the
contactor.
(see
Advertisement
