APPENDIX F:
EARTHING
Introduction
The following decision tree and the accompanying diagrams can be used to establish the earthing
needed for your system.
Definitions
Intrinsic Safety Earth The earthbar connection to the zener barriers. It
should have its own unique cable connection back to
a central grounding point.
Isolated power supply A power supply where the 0V line is not connected
to the earth terminal.
The internal power supply in Vortex is isolated.
Galvanic isolator An alternative to a zener barrier that does not require
the high integrity earth.
Examples of galvanic isolators are:
MTL 5041 Repeater Power Supply 4/20mA for 2-
wire transmitters, which is used with 2-wire 4/20mA
gas detectors
MTL 5061 Fire/Smoke Detector Interface, two-
channel, loop powered, which is used for fire loops.
Zener barrier A device used to implement a safe interface between
a safe and a hazardous area. The device limits the
amount of voltage and current that can enter the
hazardous area, in order that sparks or heat caused
by an electrical fault in the safe area do not cause an
ignition hazard in the hazardous area. Zener barriers
require a high integrity earth (ground) connection,
sometimes known as the Intrinsic Safety Earth.
An example of a zener barrier is the MTL 728 shunt
diode safety barrier.
Questions
These questions are referred to in Figure 20 The possible answers are also listed. Answer the questions
and follow the tree until it refers to the diagrams which should be used as a guide to wiring and
earthing requirements.
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