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System Wiring Notes
Fig. 1: System wiring for 3 wire Shunt-Diode Barriers. (Page 5)
Fig. 2: System wiring for 2 wire Shunt-Diode Barriers. (Page 6)
Fig. 3: System wiring for 3 wire Isolating Interface Units. (Page 7)
Fig. 4: System wiring for 2 wire Isolating Interface Units. (Page 8)
SA = Safe Area.
HA = Hazardous Area.
SAA = Safe Area Apparatus.
CS1 = Signal Connection Supply.
CS2 = Signal Connection.
PS1 = PRT Connection Supply.
PS2 = PRT Connection.
1.
Safe Area Apparatus is unspecified except that it must not be supplied from nor contain in normal or abnormal
conditions a source of potential with respect to earth in excess of 250Volts RMS or 250Volts DC.
2.
A multi-core cable, may be used for Gas groups IIC & IIB provided the cable is screened in accordance with the
following method:
(a) All wires are individually screened.
(b) Wires are screened as pairs/threes as shown.
(c) Wires are screened as a pair and quad as shown.
(d) Wires are screened as a three and quad as shown.
(e) The outputs from Interface unit 'X' or from barriers 'A' & 'B', may be individually screened or screened together
with an overall screen as shown.
3.
The insulation material between screens must be of sufficient quality to withstand a breakdown when a voltage of
500VDC is applied across them.
Shunt-Diode Safety Barriers
4.
In all cases the cable screens must be earthed only at the Barrier.
5.
Barriers in position 'A', 'C' & 'D' may be any combination of single or dual channel Shunt Zener Diode safety
barriers ATEX certified to [EEx ia] IIC, whose output parameters are equal to or less than:-
In any barrier the output current must be limited by a resistor 'R' such that Io=Uo/R.
6.
The electrical circuits in the hazardous must be capable of withstanding an AC test voltage of 500Volts RMS to
earth or frame of the equipment, for a period of 1 minute without breakdown.
Isolating Interface Units (Galvanic isolators)
7.
Interface Unit in position 'X' is a pulse signal isolator, typically MTL 5032 or P&F KFD2-CR-Ex1.30.300. Interface
Unit in position 'Y' is a PRT temperature converter, typically MTL 5073 or P&F KFD2-TR-Ex1. The interfaces are to
be ATEX certified to [EEx ia] IIC.
8.
Because the power supplies have isolation the electrical circuit in the hazardous area need not be capable of
withstanding an AC test voltage of 500Volts RMS to earth or frame of the equipment, for a period of 1 minute
without breakdown.
9.
Typical resistor values: R1= 2K, R2= 200R
Please note that the safety instructions and certificates in this publication have been translated from English (United Kingdom).
30985018/SI
Barrier
Uo
A
28V
93mA
B
28V
Diode
C
15V
50mA
D
15V
50mA
E
15V
50mA
Typical barriers: 'A'/ 'B' MTL787, 'C', 'D', 'E' MTL 764.
Io
Po
Total A+B
0.65W
Total C+D+E
0.5W
Page 3
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