Why is the INTERLOCK- terminal not connected to the COM (circuit common) terminal in the I/O connector of TOS5300 series?

In TOS5300 series, the INTERLOCK- terminal is not connected to the circuit common (COM) terminal.
Since the INTERLOCK terminals needs to be independent to install the door switch, they are electrically isolated from other terminals of the I/O connector.

To release the interlock feature, use an open/close switch signal or a transistor/optical device by following the user’s manual (the chapter of Interlock Feature).