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Siemens AG
Entry type: FAQ Entry ID: 109779477, Entry date: 05/11/2020

How do you protect SITOP power supplies on the input side?

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There are 1-phase and 3-phase SITOP power supplies. They are protected in different ways.

1-phase SITOP power supplies
The 1-phase units have an internal fuse. It is not necessary to protect them separately on the input side. An additional external fuse on the input side is used for line protection.

For increased requirements for short-circuit resistance (100 kA) it is recommended to use Siemens switches from the 3RV2 series. For 1-phase devices, the three paths of the 3RV2 circuit breaker are looped through in series.

3-phase SITOP power supplies
The 3-phase units have no internal fuses. It is necessary to protect them on the input side. The additional external fuse on the input side is used for device and line protection.

For external protection, the requirements differ according to the permitted standards:

  • International (IEC): 3-pin coupled circuit breaker 3-16 A (for example: Siemens 5SY... - max. characteristic C) or circuit breaker 3RV2
  • North America (UL/CSA): 3 ph 3-16 A circuit breaker UL489 listed, DIVQ (for example: Siemens 3RV27.../ 3RV28...) or fuses UL248 listed, JDDZ (for example: Class CC Fuse)

Two or more SITOP power supplies can be connected to one circuit breaker, in strict compliance with the above requirements (rated max. 16 A, short-circuit trip 160 A).

Further Information
Detailed information on protecting a SITOP power supply can be found in the respective device manual or compact operating instructions:
Manuals and Compact Operating Instructions

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