STRUCTURED WIRING
General Principles
Structured wiring allows for the flexible use of a buildings cabling network to run
computers and telephones. The system is
totally flexible, in so much as the user can move apparatus from one office to another
without resorting to any engineering work The whole system is built in
accordance with the Category 5 wiring specification and only approved equipment may be
used. Cat 5 cable looks the same as telephone cable but is made to a higher
specification.
Overview of Installation
The telephone system is wired to a central patch panel consisting of RJ45
sockets. Extensions are cross connected from
the telephone system patch panel to the building wiring patch panel using RJ45 plug ended
patch cables.
These patch cables are straight connected and must not be confused with twisted cables (that look similar) that are used on ISDN equipment.
Patch cables may differ in colour and this is
for identification purposes only, as they electrically the same.
At the end of the building cable is a RJ45 socket. Telephones may have to be connected to the RJ45 socket and this may be achieved by the use of:-
 | An RJ45 to PST adapter. |
| By fitting an RJ45 plug ended cord to the telephone. |
Adapters come in three types:-
| PSTN Master, used for Exchange lines when connected to POT phones and Fax machines etc (has a ring circuit capacitor, test resistor and high voltage protector). |
| PBX Master, as above but without resistor and high voltage protector. |
| Secondary/slave adapter, used for supersets or apparatus that does not require a ring circuit capacitor. |
All sockets and patch panels should be labelled and records should be kept of all connections.
Connecting Telephone Equipment
To ensure that telephones will work when connected to a structured cabling system the
wiring must be correctly terminated at the first patch panel. Extension wiring
should be connected as follows:
| Telephone system | RJ45 socket on Patch panel |
| A | 5 |
| B | 4 |
| Earth | 1 |
Only straight patch leads should be used to cross connect between patch panels (see above diagram).
BT adaptors
For a UK telephone to be connected to an RJ45 socket a converter adapter must be used. There are two sorts - one cord ended (as shown) and the other that plugs directly into the socket.
The wiring of the adapter is shown below. There are three sorts of adaptors: PSTN, PABX Master and Secondary. Ensure that you purchase the correct version for your needs.
The PBX master is used when standard telephones are connected and the Secondary type used for Telephone System Phones.
Adapter wiring
| RJ45 Socket |
RJ45 Plug | BT Socket | |
| 1 | 1 | 4 | Recall - if wired |
| 2 | 2 | - | Ring - Not connected |
| 3 | 3 | 6 | |
| 4 | 4 | 2 | B leg |
| 5 | 5 | 5 | A leg |
| 6 | 6 | 1 | |
| 7 | 7 | - | |
| 8 | 8 | - |
Problems
Analogue telephone (POT) does not ring or only rings once:
| Earth connected wrongly in Patch panel wiring. |
| Secondary adapter used (structured wiring system). |
ISDN adapter does not work:
| Ensure that correct cable is used between ISDN adapter and RJ45 socket (should be twisted type). |