Relay monitors phase sequence and failure ( e.g monitoring of correct motor winding etc.)in 3 phaze main
HRN-55: supply from all phases, which means that function of relay is applicable also if one phase fails.
HRN-55N: supply L1-N, it means that relay also monitors break of neutral point.
HRN-55: 3 x 400 V
HRN-55N: 3 x 400 V/ 230 V