II - DCE FEL ČVUT v Praze

Mechanical Configuration of an Automation System with SIMATIC S7 Ex Modules
I/O Modules with Intrinsically-Safe Signals
C79000-G7076-C152-04
Ex i non-Ex i
> 1 mm
Ex i non-Ex i
Fig. 1-11 Routing of cables for intrinsically safe circuits
Cable routed in separate, insulating
cable ducts
Cables routed in a common cable
duct with an insulating intermediate
layer
(The solid insulating intermediate
layer of >1 mm provides reliable
isolation of the intrinsically safe lines
in accordance with EN 50020)
Where sheathed cables of intrinsically safe and non-intrinsically safe circuits
are routed together, the sheathed cable of the intrinsically safe circuit must
withstand a minimum test voltage of 1500 Vrms AC.
The high test voltage of 1500 V AC can be dispensed with if the intrinsically
safe or non-intrinsically safe circuits are enclosed in a grounded (earthed)
shield. However, the test voltage of the lines for intrinsically safe circuits
must be at least 500 V AC (between conductor-conductor-ground).
Intrinsically safe lines must be clearly marked. If a color is used, it must be
light-blue. An exception to this rule is the routing of lines within equipment,
distribution panels and switchrooms. Cables and lines thus marked must not
be used for other purposes.
In general, intrinsically safe circuits must be installed in a floating
arrangement. A connection to ground via a 15 kOhm resistor, e.g. to
discharge electrostatic charges, does not qualify as a ground. Intrinsically
safe circuits must be grounded when this is required for measurement or
safety reasons. Grounding may only take place at one point by connection to
the equipotential bonding conductor. Equipotential bonding must be provided
throughout the entire installation area of intrinsically safe circuits.
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