Individual Barrier Configuration: For applications requiring just a few phones, we recommend that the Intrinsically-Safe Telephones be purchased on an "individual” basis. Each phone (Model 262-001 or 272-001) should be ordered with its own wall-mountable Isolation Barrier Unit (Model 263-000). The Isolation Barrier Unit houses both the PCBA and the Power Supply for the telephone. For convenience, a single model number has been established to order an indoor (Model 261-001) or weatherproof (Model 271-001) combination of these units.