ABB Relion 670 Series Technical Reference Manual page 651

1MRK 505 208-UEN B
Technical reference manual
IEC1MRK002801-AA11-UTAN-RAM V1 EN
Figure 309: Binary in/out module (IOM), input contacts named XA corresponds
to rear position X31, X41, and so on, and output contacts named
XB to rear position X32, X42, and so on
The binary input/output module version with MOV protected contacts can for
example be used in applications where breaking high inductive load would cause
excessive wear of the contacts.
The test voltage across open contact is lower for this version of the
binary input/output module.
Section 17
IED hardware
645