3Com AccessBuilder 500 User Manual page 4

There are no user-replaceable fuses or user-serviceable parts inside the
unit. If you have a physical problem with the unit that cannot be solved
with problem solving actions in this guide, contact your supplier.
Disconnect the power before moving the unit.
WARNING: Twisted Pair RJ45 data port. This is a shielded RJ45 data
socket. It cannot be used as a telephone socket. Only connect RJ45 data
connectors to this socket.