Caution: Users should not attempt to make such connections themselves, but should contact the appropriate electric inspection authority, or
electrician, as appropriate."
"Notice: The Ringer Equivalence Number (REN) assigned to each terminal device provides an indication of the maximum number of terminals
allowed to be connected to a telephone interface. The termination of an interface may consist of any combination of devices subject only to the
requirement that the sum of the Ringer Equivalence Numbers of all devices does not exceed 5."
11 CS 5500 Operator’s Guide