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European Safety Systems Ltd.
Impress House, Mansell Road, Acton, London W3 7QH www.e2s.com Tel: +44 (0)208 743 8880
Document No. D202-00-501-IS
Issue 1 28-01-2024 Sheet 8 of 9
Integrity in respect of failure to close
SIL 2
System Type
A
Hardware Fault Tolerance
0
Safe Failure Fraction (credible claim)
75%
PFD (hazardous failure)
2.3 x 10
-3
Proof Test Interval
Up to 1 year
17)
Electrical System Design For Installation In
Hazardous Areas Using Zener Barriers
ATEx/IECEx & UKEx Installations:
17.1 Single Input Barrier
Where the call point switch uses a Zener barrier, as shown in
Fig below.
Fig. Single stage call point alarm using single barrier.
NEC /CEC Installations:
17.2 Single Input Barrier
Where the call point switch uses a Zener barrier, as shown in
Fig below.
Fig. Single stage call point alarm using single barrier.
1. Associated apparatus output current must be limited
by a resistor such that the output voltage current
plot is a straight line drawn between open-circuit
voltage and short-circuit current.
2. Installed should be in accordance with its
manufacturer’s control drawing and Article 504 of
the National Electrical Code (ANSI/NFPA 70) for
Canadian installation in the United States, or
Section 18 of the Electrical Code for installations in
Canada.
3. Where the cable capacitance and inductance per
foot are not known, the following values shall be
used: Ccable = 60 pF/ft., Lcable = 0.2
μ
H/ft.
4. When required by the manufacturer’s control
drawing, the associated apparatus must be
connected to a suitable ground electrode per the
National Electrical Code (ANSI/NFPA 70), the
Canadian Electrical Code, or other local installation
codes, as applicable. The resistance of the ground
path must be less than 1 ohm.
18)
Electrical System Design For Installation In
Hazardous Areas Using Galvanic Isolators
Galvanic isolators do not require a high integrity earth
connection. For small systems where a high integrity earth is
not already available, the use of galvanic isolators often
reduces the overall installation cost and simplifies design.
ATEx/IECEx & UKEx Installations:
13.1 Single Input Barrier
Where the call point switch uses a single Zener barrier, as
shown in Fig below.
Fig. Single stage call point alarm using single galvanic
isolator.
