Intrinsically safe
PP1095/2021/Issue 6
Page 4 of 8
channel devices respectively. Both versions are BASEEFA certified
under Certificate Number BAS00ATEX7087.
The galvanically isolated barrier is a two-wire device which does
not need an external power supply. Current drawn from the XP95
loop by the barrier itself is less than 2mA when loaded as specified
by the manufacturer. The housing is a DIN-Rail mounting, identical
to that used for the protocol translator.
Approved safety barriers
The system certification includes a generic specification for
barriers, two additional, individually approved barriers and two
transformer isolated current repeaters (galvanic barriers).
The generic specification is:
Any shunt zener diode safety barrier certified by BASEEFA or any
EU approved certification body to
E Ex ia IIC
Having the following or lower output parameters:
Uz = 28 V
I max:out = 93.3 mA
W max: out = 0.67 W
In any safety barrier used the output current must be limited by a
resistor ‘R’ such that
I max: out = Uz
R
Wiring and cable types
It is not permitted to connect more than one circuit in the hazardous
area to any one safety barrier and that circuit may not be connected
to any other electrical circuit.
Both separate and twin cables may be used. A pair contained in a
type ‘A’ or ‘B’ multicore cable (as defined in clause 12.2.2 of BS EN
60079-14) may also be used, provided that the peak voltage of any
circuit contained within the multicore does not exceed 60 V.
The capacitance and either the inductance or the inductance
to resistance (L/R) ratio of the hazardous area cables must not
exceed the parameters specified in Table 4. The reason for this
is that energy can be stored in a cable and it is necessary to use
cable in which energy stored is insufficient to ignite an explosive
atmosphere.
To calculate the total capacitance or inductance for the length of
cables in the hazardous area, refer to Table 3, which gives typical
per kilometre capacitance and inductance for commonly used
cables. (
Note:
All XP95 I.S. devices have zero equivalent capacitance
and inductance
).
Table 3: Examples of electrical characteristics of cables commonly used in fire protection systems
Cable Type
Core
Size mm2
Conductor Resistance
Ohm/km/Core
Inductance
mH / km
Capacitance �F / km
Sheath
Resistance
Ohm / km
Core to
Core
Core to
Sheath
MICC Pyrotenax Light Duty
2
1.5
12.1
0.534
0.19
0.21
2.77
MICC Pyrotenax Heavy Duty
2
1.5
12.1
0.643
0.13
0.17
1.58
Pirelli FP200
all
1.5
12.1
-
0.08
0.15
-
PVC Sheathed and Insulated to
BS 6004
all
1.5
12.1
0.77
0.09
-
-
Table 4: Limits for energy stored in cables
Group
Capacitance
�F
Inductance
mH
L/R Ratio �H / Ohm
IIC
0.083
4.2
55
IIB
0.65
12.6
165
IIA
2.15
33.6
440
