Your premises may already be wired with parallel extension telephones, or you may plan to add extension telephones to your line, as well as your machine. While the simplest arrangement is a straightforward parallel connection, there are some problems with this. The most obvious is inadvertent interruption of a fax transmission caused by someone picking up an extension telephone to make an outgoing call. Also, the remote activation code feature may not operate reliably in such a simple configuration.

This machine also may be set to make a delayed transmission (i.e. a transmission at a pre-set time). This pre-set job may coincide with someone picking up an extension handset.

These 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 fig. 2). In this configuration the machine can always detect whether a telephone is in use. Thus 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 put into the modular socket of the white “T”-shaped connector provided as part of the line cord assembly.

Inadvisable connection of extension sockets (Fig. 1.)

1. Extension socket
2. Master socket
3. Incoming line

Recommended connection of extension sockets (Fig. 2.)

1. Extension socket
2. Master socket
3. Incoming line

The fax machine must be plugged into the master socket.

These telephones are now connected as external devices, because they are connected to the fax machine via the T-connector.