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Siemens AG
Entry type: FAQ, Entry ID: 109741643, Entry date: 02/24/2017
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Power losses / contact resistance for 3SB1 / 3SB2 / 3SB3 / 3SE3 / 3SE5 / 3SU1

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This entry contains information about contact resistance for 3SB1 / 3SB2 / 3SB3 / 3SE3 / 3SE5 / 3SU1 units

QUESTION:

How high is the contact resistance for 3SB1 / 3SB2 / 3SB3 / 3SE3 / 3SE5 / 3SU1 units?

ANSWER:

For as-new 3SB1 / 3SB2 / 3SB3 / 3SE3 / 3SE5 / 3SU1 devices, contact resistance is, on average, 20 milliohms, however, contact resistances of up to 100 milliohms are permissible.

Currents of 10 mA are typical in the control circuit when connected to a PLC.
At 10 mA, power losses are only 0.002 mW (P = I² * R).

Here are some general details regarding power loss:

- Contact power loss is proportional to the current load
- The total power loss is the sum of the power loss of the contacts + power loss of the clamping point + power loss of the supply cable
- The power loss of the contact is largely determined by its condition (e.g. oxide layers).

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