Campbell Scientific SC932A 9-Pin to 9-Pin RS-232 Interface - Manual (Page 9)

SC932A 9-Pin to RS-232-DCE Interface
5
6361 includes hardware for mounting to ground lug of CSI enclosures
models ENC 10/12, ENC 12/14, or ENC 16/18). Spark gap wiring is
straight through such that pin to pin continuity exists between the two
modems. If the modems are installed entirely within a building, the
transient spark gap protection is probably not needed.
FIGURE 3. Installation of Spark Gap Protection