2
benzine, benzol, butane, ethylene dichlo-
ride, gasoline, hexane, lacquer solvent
vapors, naphtha, natural gas, propane,
propylene, styrene, vinyl acetate, vinyl
chloride, or xylenes.
Group E
: Atmospheres containing combustible metal
dusts regardless of resistivity, or other
combustible dusts of similarly hazardous
characteristics having resistivity of less than
10
5
ohm/centimeter.
Group F:
Atmospheres containing carbon black,
charcoal, coal, or coke dusts which have
more than 8 percent total.
Group G:
Atmospheres containing combustible dusts
having resistivity of 10
5
ohm/centimeter or
greater.
Description
The heat and smoke actuated detectors are located
in a hazardous location. A Class B two wire detector
circuit extends back to the non-hazardous location
where connections are made to terminals 5 (output
ground) and 1 (output) of the Diode Shunt Barrier
located in the system control panel cabinet (or in a
separate enclosure). Under normal operating condi-
tions voltage and current in the hazardous locations
are at levels known to be safe for intrinsically safe
electrical equipment operating in Group A atmo-
spheres. However, should any combination of two
independent faults occur
(plus field wiring failures)
within the system, the barrier will prevent the appear-
ance of excessive voltage and currents in the hazard-
ous location. The ZS-30 module is part of a low
voltage control panel and is connected to the barrier
and detector circuit. The module is mounted on a
System 3 panel along with the control unit. The
intrinsically safe module is interconnected to System 3
modules bus wire cable and draws its power from the
System 3 power supply through the control unit. The
module provides regulated voltage to the detectors in
the hazardous locations through the Diode Shunt
Barrier. It also detects and generates trouble and
alarm conditions. Alarm and trouble conditions are
indicated by red and yellow LEDs on the panel on the
intrinsically safe zone, and corresponding high-going
electronic signals are passed to the control unit. The
detector circuit consists of up to ten DI-3IS ionization-
type smoke detectors or up to five S121 or S122 flame
detectors, in addition to any number of mechanical
(non-energy storing) shorting devices. The detector
circuit is terminated by a 5.6K ohm end of line resistor.
Installation
Refer to Figures 1-3 below when installing the ZS-30.
The Diode Barrier may be located in the main control
panel or in a separate enclosure; but, in either case,
care must be exercised in installation.
System 3 chassis ground must be removed.
Each
duplicate (redundant) grounding conductor should be
connected to the grounding connections on the barrier
device and run directly to the ground electrode not
via other paths leading to that electrode.
Each ground wire must be 14 or 18 AWG wire and
should not exceed an impedance of 1 ohm. All ground
wires should be connected separately to the same
ground location. Wiring connected to the barrier output
Figure 1
Field Assembly of Diode Barrier
