Siemens Industry Online Support
Siemens AG
Entry type: FAQ Entry ID: 21653905, Entry date: 09/18/2018

3RT1/3RT2 contactors - Statement on power losses

  • Entry
  • Associated product(s)
This entry contains information on power losses with 3RT1/3RT2 contactors


How can the power loss of the 3RT1 and 3RT2 contactors  be computed for the heat calculation in the switchgear?



The power losses of the 3RT1 and 3RT2 contactors comprise the power loss from the contactor drive plus the power loss of the main circuits.

-   For DC-operated contactors = holding power in W
-   For AC-operated contactors = holding power in VA x cos phi

Example for contactor 3RT2015-1BB41
Drive (holding power): Pv = 4.0 W

Main circuit: Pv = 0.4 W for one circuit, makes 3 x 0.4 W = 1.2 W for 3 loaded circuits
Total power loss =  Power loss of drive + power loss of loaded  circuits
Total power loss =  4 W + 1.2 W = 5.2 W

You can find power loss data (contactor drive plus main circuits) in the product data sheet (available from the Industry Mall 
or SIOS ).

They are also included in the free SIMARIS therm tool.
SIMARIS therm enables easy calculation of power losses for designing industrial control panels.

Security information
In order to protect technical infrastructures, systems, machines and networks against cyber threats, it is necessary to implement – and continuously maintain – a holistic, state-of-the-art IT security concept. Siemens’ products and solutions constitute one element of such a concept. For more information about cyber security, please visit
Rate entry
no rating
Requests and feedback
What do you want to do?
Note: The feedback always relates to the current entry / product. Your message will be forwarded to our technical editors working in the Online Support. In a few days, you will receive a response if your feedback requires one. If we have no further questions, you will not hear from us.