Page 621 - Wago_Rail-MountedTerminalBlockSystems_Volume1_2015_US.pdf

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Special Requirements No special approval is required for ter- The insulation between an intrinsically
“Intrinsic safety Ex i” minal blocks used as simple electrical safe circuit and the chassis of an electri-
The European Standard EN 60079-11 – equipment for protection type “Ex i”, as cal equipment or parts, which may be
Classification VDE 0170, Part 7 – con- they do not contain a voltage source and grounded, has to withstand an effective
tains special requirements for the design precise information is available concern- AC voltage corresponding to double the
and testing of electrical equipment with ing electrical data and temperature rise value of the voltage of the intrinsically
protection type – Intrinsic safety “i” – for performance. safe circuit or a minimum of at least
use in hazardous areas. The terminal blocks must be identifiable, 500V, depending on which value is high-
for example by their type designation, er.
A circuit is designated as “intrinsically and the following design requirements The insulation between an intrinsically
safe” when under normal operating con- must also be upheld: safe and a non-intrinsically safe circuit
ditions and in the event of defined faulted ● The air distance between bare, con- has to withstand an effective AC voltage
conditions, no sparks and no thermal ducting parts of terminal blocks of of 2 x nominal value (U) +1 kV or a mini-
effects can cause an ignition in a defined different intrinsically safe circuits has mum of 1.5 kV, whereby U represents the
potentially explosive atmosphere. to be equal or higher than the values total of the effective voltages of the intrin-
specified in the standard. In addition, sically safe and the non-intrinsically safe
A distinction is made here between: the air distances between the terminal circuit.
● intrinsically safe electrical equipment blocks must be so that the air distances Short circuit between different intrinsically
when all circuits are intrinsically safe between bare, conducting parts of the safe circuits could cause dangerous con-
and connected external conductors is at ditions. The insulation between these cir-
● associated electrical equipment includ- least 6 mm for one measurement. Each cuits should withstand an effective volt-
ing both intrinsically and non-intrinsical- possible motion of metallic parts that age of at least 500VAC or 2UAC where
ly safe circuits, and being designed are not rigidly fixed must be consid- U is the total of the effective voltages for
such that the non-intrinsically safe cir- ered. the related circuits.
cuits cannot affect the intrinsically safe ● When a possible connection has not In accordance with the Electrical Installa-
ones. been considered during safety analy- tions Design Guideline DIN EN 60079-
sis, the minimum clearance between 14 (VDE 0165-1), stranded and fine-
Intrinsically safe electrical equipment and grounded metallic or other conducting stranded conductors used in intrinsically
intrinsically safe parts of associated elec- parts and the uninsulated conducting safe circuits shall be protected against
trical equipment are classified at protec- parts of the conductors that are con- splayed ends (e.g., via ferrules or pin ter-
tion level “ia” or “ib.” nected to the terminal blocks must be minals) or by the type of terminal
Products classified Ex “ia” shall not ignite 3 mm. blocks used. Tinning the conductor end
when current is applied in the following ● Terminal block marking must be unique alone is not permissible.
cases: and clearly visible. If a color is used Gastight tinned copper ferrules or tinned
a) During fault-free operation, with those for this, the color must be light blue copper pin terminals are recommended
non-discreet faults present that result in (similar to RAL 5015). when connecting fine-stranded conduc-
the most adverse condition. Note also when using terminal blocks: tors to terminal blocks in corrosive atmo-
b) During fault-free operation and with a Terminal blocks used for intrinsically safe spheres.
discreet fault, plus those non-discreet circuits must be isolated from those used
faults that result in unfavorable condi- in non-intrinsically safe circuits. This is
tions. accomplished by several accepted meth-
c) During fault-free operation with two ods. First, intrinsically safe circuits are
discreet faults, plus those non-discreet separated by at least 50mm of air space
faults that result in the most adverse from non-intrinsically safe circuits.
conditions.
Second, intrinsically safe circuits are
Products classified Ex “ib” shall not ignite housed in a separate enclosure. Third,
when current is applied in the following intrinsically safe terminal blocks are sepa-
cases: rated from non-intrinsically safe terminal
a) During fault-free operation, with non- blocks by either an insulated partition or
discreet faults present that result in the grounded metal partition. The partition
most adverse condition; size must allow for either 1.5mm or less 14
b) During fault-free operation, with a distance from the sides of the housing or
discreet fault present, plus those non- provide at least 50mm of creepage dis-
discreet faults that result in the most tance between the intrinsically and non-
adverse condition. intrinsically safe circuits in all directions.