Specifications

Page 17–2
FOCUS System Manual
Figure 17–1. HCB/HCB-1 Interface Module
for Two-Terminal Applications.
Figure 17–2. SPD Interface Module
for Two-Terminal Applications.
17.2.2 Interface Connections
The interface modules on the rear of the FOCUS
chassis are different for HCB/HCB-1 and SPD
relays. They are also different for two- and three-
terminal line applications. These interface
modules are shown in Figures 17-1 to 17-4. As
Figure 17-2 shows, the interface module for the
SPD two-terminal application has a 4/1 matching
transformer, enclosed in a bright metal can,
mounted on it. This transformer is not present on
the version used for an HCB/HCB-1 two-terminal
application, which is shown in Figure 17-1.
Because the switches used in the metallic
pilot wire application are not designed to
work at low voltages and currents, they can
create more problems than they help solve. A
small amount of oxidation on the switch
contacts will have a large effect on system
operation. You can make your system more
reliable by removing the test milliammeter
and switch. Much of its original purpose was
to let you check for pilot wire errors after
maintenance on the pilot wire. Because the
wiring between the relay and FOCUS is local,
and FOCUS cannot reverse the signal, the test
circuits are not required. You may use other
methods to check out the current transformer
wiring of the initial installation.
CAUTION !