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Sepam 80 - can I use 64REF, 51N, and 51G protection on the same relay for a 4-wire low-voltage system (e.g., MV-LV transformer)?

Some of the Sepam 80 protection functions can be used for low-voltage installations, as explained in the Protection Functions User Manual.

However, some of the limitations in terms of supported wiring configurations are not explicitly stated in the user manual.

Also - there are not always warning in SFT2841 to inform the user that a certain configuration is not possible.

Please see the attached file for an example where the 64REF, 51N, and 51G protection functions cannot be achieved using a single Sepam 80 relay.  In fact, the protection functions could be applied correctly with a single relay, but some wiring modifications are required.

As explained in the attached file, the key points to keep in mind are as follows:

- for a 4-wire low-voltage system (e.g., TN-C, or TN-S), the CT's used for 51N and 51G should not be the same.  They should be installed at different positions.
- all supported configurations for the 64REF function in low-voltage use the CCA634 CT adaptor.  So, the corresponding Io input (for the CSH120/200) cannot be used.
- the SFT2841 software (as of version 15.1) does not give any warnings if you create a configuration which enables all of these functions.  It is assumed that the project team will check the wiring to ensure that the CSH120/200 (Io) input will not be used if a CCA634 is installed, for example.

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