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Chapter 7
58
Using extension telephones (U.K.
only)
7
Your premises may already be wired with
parallel extension telephones (those
connected to sockets in other rooms in the
building), or perhaps you intend to add
extension telephones to your line. While the
simplest arrangement is a parallel
connection, there are some reasons why this
arrangement may cause problems.
The most common problem, is someone
picking up an extension telephone while the
machine is trying to send a fax.
Such problems can easily be eliminated, if
you arrange modification of your extension
wiring circuit, such that extension devices are
connected “downstream” of your machine, in
a master/slave configuration (see figure 2). In
such a configuration, this machine can
always detect whether a telephone is in use,
so it will not attempt to seize the line during
that time. This is known as “telephone off-
hook detection”.
The inadvisable configuration is shown in
figure 1, and the recommended master/slave
configuration is shown in figure 2.
This new connection configuration can be
arranged by contacting BT, Kingston upon
Hull Telecommunications, your PBX
maintainer or a qualified telephone
installation company as appropriate. Simply
explained, the extension telephone circuit
should be terminated on a normal modular
plug (BT 431A style), which in turn should be
inserted into the modular socket of the white
“T”-shaped connector provided as part of the
line cord assembly.
Figure 1:
7
1 Extension socket
2 Master socket
3 Incoming line
Figure 2: Recommended connection of
extension sockets
7
1 Extension socket
2 Master socket
3 Incoming line
These phones are now connected as external
devices as shown on page 57, because they
are connected to the fax machine via the T-
connector.
FAX
12
3
1
FAX
12
3
1