IEC TS 60079-39:2015

IEC TS 60079-39 ®
Edition 1.0 2015-06
TECHNICAL
SPECIFICATION
colour
inside
Explosive atmospheres –
Part 39: Intrinsically safe systems with electronically controlled spark duration
limitation
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IEC TS 60079-39 ®
Edition 1.0 2015-06
TECHNICAL
SPECIFICATION
colour
inside
Explosive atmospheres –
Part 39: Intrinsically safe systems with electronically controlled spark duration

limitation
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.260.20 ISBN 978-2-8322-2734-3

– 2 – IEC TS 60079-39:2015 © IEC 2015
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references. 8
3 Definitions . 9
4 Power-i architecture . 10
5 Requirements for Power-i devices . 11
5.1 General . 11
5.2 Power-i source . 11
5.3 Power-i field device . 13
5.4 Power-i wiring . 14
5.5 Power-i terminator . 15
5.6 Test instruments for Power-i loop check . 15
5.7 Power-i application classes . 15
6 System requirements . 16
6.1 Selection of the permissible Power- i current class of the Power-i source . 16
6.2 Verification of a Power-i system . 17
7 Assessment and testing . 19
7.1 Procedure to define safety-relevant parameters . 19
7.2 Type test . 20
7.3 Routine test . 20
8 Marking of Power-i devices . 20
8.1 General . 20
8.2 Examples of marking . 20
9 Instructions. 21
Annex A (normative) Assessment of Power-i safety parameters . 22
A.1 General . 22
A.2 Power-i specific test equipment . 22
A.2.1 Power-i universal test equipment . 22
A.2.2 Power-i dummy load . 23
A.3 Determination of the safety-relevant parameters for Power-i devices and
Power-i wiring . 24
A.3.1 General . 24
A.3.2 Safety-relevant parameters for the Power-i source . 24
A.3.3 Safety-relevant parameters for the Power-i field devices . 31
A.3.4 Safety-relevant parameters for Power-i wiring . 34
A.3.5 Safety-relevant parameters for the Power-i terminator . 36
Annex B (informative) Explanation and details of the Power-i basic concept . 37
B.1 Physical basics of an ignition . 37
B.2 Output characteristics of a Power-i source . 39
B.3 Measurement and scientific results as basis for Power- i minimum ignition
values . 41
B.3.1 Test setups for the determination of the ignition probability . 41
B.3.2 Result of the spark ignition tests and their implementation in Table 3 . 43

Annex C (informative) Examples of Power-i devices and systems . 46
C.1 Power-i application for a solenoid valve . 46
C.2 Example of a generally designed Power-i source . 47
C.3 Example of a Power-i field device . 47
C.4 Example of a Power-i dummy load . 48
C.5 Example of a Power-i terminator . 48
Annex D (informative) Example of interconnection of Power-i devices including
Power-i wiring to a Power-i system . 50
D.1 Specific aim and given values . 50
D.2 Solution example . 50

Figure 1 – The simplest Power-i architecture . 10
Figure 2 – Example of complex Power-i concept architecture . 11
Figure 3 – Elements of a Power-i source with voltage and current limitation . 12
Figure 4 – Example of a universal Power-i field device (basic structure) . 14
Figure 5 – Basic assessment procedure for a Power-i system . 19
Figure A.1 – Basic principle of the Power-i universal test equipment . 23
Figure A.2 – Pulse output between terminals 3 and 1 of Figure A.1 . 23
Figure A.3 – Basic principle of a Power-i dummy load . 24
Figure A.4 – Basic principle of the equipment for the determination of the response
time t . 25
resp-source
Figure A.5 – Example of an oscillogram to determine the response time t . 26
resp-source
Figure A.6 – Test equipment for the determination of the assessment factor AF
source
(basic principle) . 27
Figure A.7 – Test equipment for the assessment factor test for Power-i source . 28
Figure A.8 – Example of an oscillogram from a test of a Power-i source with an
assessment factor AF = 8,29 for a break spark . 29
Figure A.9 – Test equipment for transition pulse test of a Power-i source . 30
Figure A.10 – Test equipment for the determination of the assessment factor
AF for Power-i field devices (basic principle) . 32
field device
Figure A.11 – Test equipment for the transition pulse test of Power-i field devices . 33
Figure A.12 – Evaluation parameter of test pulse U for transition pulse test . 34
pulse
Figure A.13 – Test equipment for the determination of the response time of the Power-
i trunk t (basic principle) . 35
resp-trunk
Figure B.1 – Example of a typical trace of a break spark supplied with a linearly limited
source . 38
Figure B.2 – Example of a typical trace of a break spark limited by a Power-i source . 38
Figure B.3 – Example of output set of characteristic curves of a Power-i source during
load connection . 40
Figure B.4 – Basic principle of a Power-i power source for the voltage threshold return
mode . 41
Figure B.5 – Example of output set of characteristic curves of a Power-i source in the
case of a failure . 41
Figure B.6 – Test setup with STA for break sparks . 42
Figure B.7 – Test setup with STA for make sparks . 42
Figure B.8 – Power-i ignition values for voltage class 24V (24 VDC) . 43
Figure B.9 – Power-i ignition values for voltage class 32V (32 VDC) . 44

– 4 – IEC TS 60079-39:2015 © IEC 2015
Figure B.10 – Power-i ignition values for voltage class 40V (40 VDC) . 44
Figure B.11 – Ignition energy in relation to the used hydrogen percentage in the gas
mixtures . 45
Figure C.1 – Simple solenoid valve Power-i application (example) . 46
Figure C.2 – Example of a generally styled Power-i field device . 47
Figure C.3 – Example of a V-limitation unit (level of protection “ib”) . 48
Figure C.4 – Example of a Power-i dummy load . 48
Figure C.5 – Example of a Power-i terminator . 49

Table 1 – Definition of Power-i voltage classes . 16
Table 2 – Definition of Power-i current classes . 16
Table 3 – Permitted combinations of Power-i application classes for Power-i sources
as a function of the system response time for all Groups (n.a. = not allowed) . 17
Table 4 – Power-i current classes of Power-i field devices or Power-i terminators
matching the current class of the Power-i source . 18
Table 5 – Relevance for Power-i test procedures . 20

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXPLOSIVE ATMOSPHERES –
Part 39: Intrinsically safe systems with electronically
controlled spark duration limitation

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC TS 60079-39, which is a technical specification, has been prepared by subcommittee
31G: Intrinsically safe apparatus, of IEC technical committee 31: Equipment for explosive
atmospheres.
– 6 – IEC TS 60079-39:2015 © IEC 2015
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
31G/236A/DTS 31G/242/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60079 series, published under the general title Explosive
atmospheres, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
INTRODUCTION
This part of IEC 60079, which is a Technical Specification, is being issued as a “prospective
standard for provisional application” in the field of Explosive Atmospheres – Intrinsically safe
systems with electronically controlled spark duration limitation because there is an urgent
need for guidance on how standards in this field should be used to meet an identified need.
Intrinsically safe systems with electronically controlled spark duration can provide more power
available in intrinsically safe circuits while maintaining the level of protection “ib” or “ic”. In
addition to limiting the voltage and current (similar to conventional intrinsically safe circuits),
the duration of the spark is limited, which also restricts the amount of energy available for
ignition.
The general requirements for the installation of IS equipment are applicable to Power-i
circuits.
This new technology allows an expansion in the field of industrial applications using the type
of protection Intrinsic Safety ‘i.
This technology, however, requires a new and more extensive approach of the type of
protection Intrinsic Safety “i”.

– 8 – IEC TS 60079-39:2015 © IEC 2015
EXPLOSIVE ATMOSPHERES –
Part 39: Intrinsically safe systems with electronically
controlled spark duration limitation

1 Scope
This Technical Specification specifies the construction, testing, installation and maintenance
of Power-i apparatus and systems which utilise electronically controlled spark duration
limitation to maintain an adequate level of intrinsic safety.
This Technical Specification contains requirements for intrinsically safe apparatus and wiring
intended for use in explosive atmospheres and for associated apparatus intended for
connection to intrinsically safe circuits entering such atmospheres.
This Technical Specification excludes the level of protection “ia” and the use of software-
controlled circuits.
This Technical Specification applies to electrical equipment utilising voltages not higher than
40 V d.c. and a safety factor 1,5 for Groups IIB, IIA, I and III. It is also applicable to Group IIC
“ic” apparatus with a safety factor 1,0. Group IIC “ib” apparatus with a safety factor 1,5 are
restricted to voltages up to 32 V d.c.
This type of protection is applicable to electrical equipment in which the electrical circuits
themselves are incapable of causing an explosion of the surrounding explosive atmospheres.
This Technical Specification is applicable to intrinsically safe apparatus and systems which
utilise electronically controlled spark duration limitation with the aim of providing more
electrical power while maintaining an adequate level of safety.
This Technical Specification is also applicable to electrical equipment or parts of electrical
equipment located outside hazardous areas or protected by another type of protection listed
in the IEC 60079 series, where the intrinsic safety of the electrical circuits in explosive
atmospheres depends on the design and construction of such electrical equipment or parts of
such electrical equipment. The electrical circuits located in the hazardous area are evaluated
for use in such locations by applying this Technical Specification.
This Technical Specification supplements and modifies the requirements of IEC 60079-0,
IEC 60079-11, IEC 60079-14, IEC 60079-17 and IEC 60079-25.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60079-0, Explosive atmospheres – Part 0: Equipment – General requirements
IEC 60079-11, Explosive atmospheres – Part 11: Equipment protection by intrinsic safety "i"
IEC 60079-14, Explosive atmospheres – Part 14: Electrical installations design, selection and
erection
IEC 60079-25, Explosive atmospheres – Part 25: Intrinsically safe electrical systems
3 Definitions
For the purpose of this document, the terms and definitions given in IEC 60079-0 and
IEC 60079-11, as well as the following apply.
3.1
Power-i
intrinsically safe concept where the level of protection is provided by voltage and current
limitation and additional electronically controlled spark duration limitation
Note 1 to entry: Power-i contains Power-i devices and Power-i wiring.
Note 2 to entry: Power-i encompasses electric circuits which in the Power-i mode operate with voltage and
current values which can exceed the values defined in IEC 60079-11.
3.2
Power-i device
Power-i source, Power-i field device(s) and (if applicable) Power-i terminator
3.3
Power-i terminator
unit to prevent reflections of voltage and current waves at the end of the Power-i wiring
Note 1 to entry: The Power-i terminator is only relevant where data transmission uses the Power-i wiring.
3.4
Power-i source
power supply for Power-i devices providing shutdown of power in case of faults
Note 1 to entry: Operating in two modes: Power-i mode and shutdown mode.
3.5
Power-i field device
device that is connected to one Power-i source via Power-i wiring
Note 1 to entry: Power-i field devices can have additional connections to other devices (e.g. loads).
3.6
Power-i mode
operating mode of the Power-i source delivering the rated Power-i output power
Note 1 to entry: In this mode the values of permitted voltage and current can exceed the values of curves and
tables stated in IEC 60079-11.
3.7
shutdown mode
operating mode of the Power-i source after a spark event has been detected
3.8
spark pulse
information resulting from a spark event in the Power-i system
Note 1 to entry: A distinction is made between the make spark pulse and the break spark pulse.

– 10 – IEC TS 60079-39:2015 © IEC 2015
3.9
Power-i response time
3.9.1
t
resp-source
maximum delay time between the detection of the spark pulse and reaching the shutdown
mode (only relevant for the Power-i source)
3.9.2
t
resp-trunk
propagation time of the trunk cable used (only relevant for Power-i wiring)
3.9.3
t
resp-system
time between the occurrence of a spark and the reduction of the spark power to safe
operation in the shutdown mode in a Power-i system
3.10
assessment factor AF
factor of attenuation or sensitivity of Power-i devices and Power-i wiring
Note 1 to entry: The assessment factor has to be distinguished between:
– Assessment factor for Power-i field devices, for the Power-i terminator and for Power-i wiring: In these cases
the assessment factor is a parameter for the attenuation of a spark pulse.
– Assessment factor for the Power-i source: In this case the assessment factor is a parameter defining the
sensitivity for the detection of a spark pulse.
Note 2 to entry: The assessment factor should be expressed in logarithmic units.
4 Power-i architecture
In a Power-i system only one active Power-i source shall be connected via Power-i wiring to
supply one or several Power-i field devices. The simplest structure consists of one active
Power-i source, Power-i wiring and one Power-i field device (see Figure 1).
The use of redundant power supplies which present one effective source of power is
permitted.
IEC
Figure 1 – The simplest Power-i architecture
A Power-i system may be extended to a complex system as shown in Figure 2.

IEC
Figure 2 – Example of complex Power-i concept architecture
NOTE The Power-i field device Sn is identical to Power-i field device S1, S2-1 or S2-2 in terms of the connection
to Power-i wiring but is shown with additional output/input terminals. These terminals are subject to requirements
of a type of protection prescribed by the IEC 60079 series suitable for the applications.
5 Requirements for Power-i devices
5.1 General
Power-i has to be considered as a system. Therefore the following requirements for all
Power-i devices apply:
a) The detection of the spark pulse shall not be invalidated during static or transient
conditions (e.g. soft start) – neither by the Power-i wiring nor by the Power-i devices;
therefore Power-i requires the consideration of the whole system.
b) All Power-i devices and the Power-i wiring shall be assessed and tested in accordance
with Annex A.
c) All Power-i devices shall be classified in accordance with 5.7.
d) Power-i devices shall meet the requirements of IEC 60079-0, IEC 60079-11 and
IEC 60079-25 as applicable in addition to other IEC 60079 standards (e.g. IEC 60079-7,
IEC 60079-18 if applicable).
e) The application of these requirements shall additionally take into account any effect in
timing and sensitivity of the safety function of the Power-i devices due to temperature
effects and component tolerance.
f) Faults determined to be the most onerous (e.g. for timing, sensitivity etc.) for the safety
function of Power-i devices shall be applied to equipment for all tests required by this
Technical Specification.
5.2 Power-i source
There shall be only one active Power-i source per Power-i system. The Power-i source shall
be placed at one end of the Power-i wiring (trunk).
A Power-i source shall detect make-sparks (sparks occurring when short-circuiting an
𝑑𝑑
electrical circuit causing a current change + ) and break-sparks (sparks occurring when
𝑑𝑑
𝑑𝑑
opening an electrical circuit causing a current change − ) and it shall provide a fast
𝑑𝑑
shutdown of the output power when a spark pulse occurs. Figure 3 shows the core elements
of a Power-i source with an upstream safety-relevant voltage and a current limitation unit.

– 12 – IEC TS 60079-39:2015 © IEC 2015
In all modes of operation where the intrinsically safe values based on conventional power
limitation according to IEC 60079-11 and IEC 60079-25 are exceeded, the detection of current
𝑑𝑑
changes ± shall not be invalidated. This includes the transition phase from the safe mode to
𝑑𝑑
the Power-i mode.
𝑑𝑑
NOTE A current change might be suppressed in the constant current mode; therefore a spark cannot be
𝑑𝑑
detected in this mode.
IEC
Figure 3 – Elements of a Power-i source with voltage and current limitation
The Power-i source shall conform to the following safety-relevant requirements:
a) The Power-i source output current I and output voltage U limited by the
O-source O-source
voltage and current limitation shall meet the requirements of Table 1 and Table 2.
b) The Power-i source shall be capable of detecting dynamic changes of the output current
𝑑𝑑
I � as defined in A.3.2. The source shall react with a subsequent transition from
O
𝑑𝑑
Power-i mode to shutdown mode.
c) In the shutdown mode the value of the output current I may be zero but shall not
shutdown
exceed 50 % of the permissible current I based on IEC 60079-11 or IEC 60079-25
O-IEC
with the applicable safety factor for the appropriate Power-i voltage class; in this case the
following equation applies.
I = I ≤ 0,5I
.
shutdown O−source O−IEC
d) Within 20 µs of the spark disturbance information arriving at the Power-i source, the
output current of the Power-i source shall be equal to or less than 75% of the I -value
O-IEC
within the first 20 µs of the transition to shutdown mode a transient output current
I of 75 % of the I value is allowed (see Figure A.5); in this case the
shutdown-20µs O-IEC
following equation applies:
I = I ≤ 0,75I
.
shutdown−20µs O−source O−IEC
e) The transient output voltage overshoot U during shutdown mode shall not
overshoot-40µs
exceed the rated output voltage U by more than 6 V for a maximum duration of
O-source
40 µs. In this case the following equation applies:
U ≤U + 6V
.
overshoot −40µs O−source
f) The Power-i source shall meet the requirements of the test procedures of A.3.2.
g) The following components of the Power-i source (see Figure 3) are safety relevant and
shall meet the requirements of 5.1 a) and d) for the respective type of protection:
• output voltage limitation U and output current limitation I ;
O-source O-source
𝑑𝑑 𝑑𝑑
• + detector and − detector;
𝑑𝑑 𝑑𝑑
• logic and
• electronic switch.
h) The output circuit of a Power-i source shall be isolated from earth. The requirements for
the isolation shall be taken from IEC 60079-11.
5.3 Power-i field device
Power-i field devices consist of a decoupling device and the actual load. Power-i field devices
shall decouple the load from the Power-i wiring.
The design of a Power-i field device shall ensure the detection of a spark pulse in accordance
with this Technical Specification.
Power-i field devices shall meet the following safety-relevant requirements:
a) They shall ensure that both, make-sparks and break-sparks, are not attenuated in any way
that the detection by the Power-i source is invalidated.
b) Under normal or fault conditions as specified in IEC 60079-11 the power-i field device
shall remain passive, that is the terminals shall not be a source of energy to the system
except for a leakage current not greater than 50 µA.
The consideration of Li and Ci for Power-i field devices based on IEC 60079-11 is not
required. This is taken into account in the test procedures described in A.3.3.
c) They shall have an appropriate type of protection in accordance with IEC 60079-0 for the
respective explosive atmosphere in which they are used.
d) They shall have safety-relevant parameters determined in accordance with A.3.3.
NOTE Due to parallel connection with Power-i wiring, the Power-i response time for field devices is
negligible.
e) All components determinant for both the assessment factor AF and the result of
field device
the transition pulse test (A.3.3.4) shall meet the requirements of 5.1 a).
f) The input circuit of a Power-i field device shall be isolated from earth. The requirements
for the isolation from earth shall be taken from IEC 60079-11.
As an example the Power-i field device shown in Figure 4 conforms to the requirements
mentioned above and can be used for a wide field of applications. The field device in Figure 4
consists of a decoupling device in combination with an arbitrary load.
The basic structure of the Power-i field device depicted in Figure 4 shows the elements
necessary to ensure that both make and break sparks are not attenuated in such a way that
the detection by the Power-i source is invalidated.
In Figure 4 inductance L, capacitance C, all diodes and the V-limitation unit are safety
relevant and shall meet the requirements of 5.1 for the appropriate type of protection.

– 14 – IEC TS 60079-39:2015 © IEC 2015

IEC
Figure 4 – Example of a universal Power-i field device (basic structure)
The V-limitation unit shall limit the positive voltage (plus (+) at point Y and minus (-) at point
X) measured from Y to X to a value of 5 V ± 1 V and shall meet the requirements in
accordance with A.3.3.4.
Practical examples of Figure 4 are shown in C.3.
5.4 Power-i wiring
The Power-i wiring shall meet the following requirements:
a) The transmission of a spark pulse shall not be impaired in a way that prevents the
detection of a relevant make or break spark pulse;
b) All Power-i wiring (Power-i trunk cable including all spur cables) shall meet the specific
requirements given in IEC 60079-11, IEC 60079-14 and IEC 60079-25;
c) Multi-core (multi-circuit) cable type C as defined in IEC 60079-25 shall be excluded for
Power-i wiring;
d) The system response time t depends decisively on the length and propagation
resp-system
delay of the Power-i trunk cable used; the requirements of Table 3 shall apply;
NOTE The cable parameters and the cable length are safety-relevant and determine the maximum response
time or the Power-i trunk (see A.3.4).
e) The maximum length of each spur is limited to 15 m. The maximum total length of all spurs
in the whole Power-i system is 50 m;
f) If the Power-i trunk cable length is less than 40 m, the value of response time of this cable
is considered to be 0,5 µs (see A.3.4.2);
in this case the spur length of each spur is limited to 10 m and the total length of all spurs
in the whole Power-i system is 20 m;
g) The calculation basis for characteristic cable impedance Z in this Technical Specification
W
is Z = 100 Ω; the permitted range of characteristic cable impedance Z for Power-i
W W
wiring is 80 Ω ≤ Z ≤ 120 Ω; the specified values for the characteristic cable impedance
W
refer to a measuring frequency of 100 kHz ± 20 %.
Section g) does not apply for f);
h) The wiring shall meet the requirements of 6 and A.3.4;

i) The use of a screen for Power-i wiring is not essential for safety; if a screen is used it may
be earthed as long as it is isolated from the Power-i circuit in accordance with the cable
dielectric strength requirements of IEC 60079-25;
j) The Power-i wiring shall be isolated from earth. The requirements for the isolation from
earth shall be in accordance with the cable dielectric strength requirements of IEC 60079-
25.
5.5 Power-i terminator
Where used, a Power-i terminator shall meet the following requirements:
a) It shall have safety-relevant parameters determined according to A.3.5.
b) All components of the Power-i terminator to prevent feeding back of the current from the
Power-i terminator into the Power-i wiring and all components determinant for the
assessment factor AF (see A.3.5.3 ) are safety relevant and shall meet the
terminator
requirements of 5.1 a).
c) It shall have a type of protection in accordance with IEC 60079-0 for use in the appropriate
explosive atmosphere.
d) The input circuit of a Power-i terminator shall be isolated from earth. The requirements for
the isolation from earth shall be taken from IEC 60079-11.
NOTE 1 The Power-i terminator ensures an ac-matching to the characteristic impedance of the connected trunk
and is only necessary in case of data transmission as for example in fieldbus systems.
NOTE 2 Due to parallel connection with Power-i wiring, the Power-i response time for terminators is negligible.
An example of a Power-i terminator is shown in Figure C.5.
5.6 Test instruments for Power-i loop check
Intrinsically safe test instruments in accordance with IEC 60079-11 may be connected directly
to Power-i wiring without further verification of the Power-i system if the following
requirements are observed:
a) the effective inductance L of 5 µH is not exceeded (L < 5 µH);
i i
b) the effective input capacitance C of 1 nF is not exceeded, additionally the input resistance
i
R shall not be less than 10 kΩ (R > 10 kΩ);
s S
c) the test instrument shall have input parameters U and I not less than the voltage and
i i
current class of the Power-i circuit;
d) the test instrument shall not be a source of energy to the system except for a leakage
current not greater than 50 µA.
Alternatively where test instruments complying with the requirements for Power-i field devices
are used, they shall be included in the verification of a Power-i system according to 6.2.
NOTE These requirements do not apply to test instruments used by the manufacturer during production, test,
repair or overhaul.
5.7 Power-i application classes
Each Power-i device shall be classified into Power-i application classes according to Table 1
and Table 2.
– 16 – IEC TS 60079-39:2015 © IEC 2015
Table 1 – Definition of Power-i voltage classes
maximum output voltage U Power-i voltage class
O-source
24 V 24V
32 V 32V
40 V 40V
Table 2 – Definition of Power-i current classes
maximum output current I Power-i current class
O-Source
0,5 A 0A5
1,0 A 1A0
1,5 A 1A5
2,0 A 2A0
2,5 A 2A5
The voltage and current values of Table 1 and Table 2 shall not be exceeded taking into
account the applicable faults according to IEC 60079-11.
Power-i field devices and Power-i terminators provided with a safety-relevant internal current
limitation can be assigned to Power-i current class 2A5.
With the internal current limitation it is not necessary that the Power-i source limits the current
to prevent overload of the Power-i field device or Power-i terminator and so it may be
connected even to a Power-i source of current class 2A5.
6 System requirements
6.1 Selection of the permissible Power- i current class of the Power-i source
The maximum permissible Power-i current class given in 5.7 depends on the selected Power-i
voltage class and on the Power-i system response time t taking into account the
resp-system
Group and safety factor required for the specific application.
Table 3 shows the permitted combinations for Groups I, II and III with the safety factors SF
1,0 and SF 1,5 depending on the respective level of protection.

Table 3 – Permitted combinations of Power-i application classes for Power-i sources
as a function of the system response time for all Groups (n.a. = not allowed)
Group voltage class permitted maximum Power-i current class of Power-i sources
+
system response time t
resp-system
safety factor
1 µs 2 µs 4 µs 6 µs 8 µs 10 µs 12 µs
SF
IIC “ib” 24 V 2A0 1A5 1A0 1A0 0A5 0A5 n.a.
SF 1,5
32 V 2A0 1A5 1A0 0A5 0A5 n.a. n.a.
IIC “ic” 24 V 2A5 2A5 2A0 1A5 1A0 0A5 0A5
SF 1,0
32 V 2A5 2A0 1A5 1A0 0A5 0A5 n.a.
40 V 2A5 1A5 1A0 1A0 0A5 n.a. n.a.
IIB “ib” 24 V 2A5 2A5 2A0 1A5 1A0 1A0 0A5
SF 1,5
32 V 2A5 2A5 1A5 1A0 1A0 0A5 0A5

40 V 2A5 2A0 1A5 1A0 0A5 0A5 0A5
IIB “ic”  SF 24 V 2A5 2A5 2A0 1A5 1A0 1A0 0A5
1,0
32 V 2A5 2A5 2A0 1A5 1A0 1A0 0A5
and
40 V 2A5 2A0 1A5 1A0 1A0 0A5 0A5
IIA, I and III
SF 1,0 and 1,5
NOTE 1 The allowed current classes in Table 3 are based on a maximum possible voltage increase
of 1 V/µs for a spark event.
NOTE 2 Example: The selected Power-i voltage class is 32 V and the selected system
response time is 2 µs:
IIC SF=1,5: maximum permitted Power-i current class for the Power-i source is 1A5 (in addition 1A0 and 0A5 are
permitted);
IIB SF=1,5: maximum permitted Power-i current class for the Power-i source is 2A5; (in addition 2A0, 1A5, 1A0
and 0A5 are permitted);
NOTE 3 The permitted values for Groups IIA, I and III are the same as allowed for Group IIB ic.

Practical examples of applications of Table 3 are shown in Annex D.
The assessment procedures specified in Annex A have been defined and optimized
specifically for the parameters in Table 3 and the above-mentioned requirements. The
interconnection conditions for various Power-i devices allow interoperability and plug-and-play
applications.
NOTE 4 Parameters beyond the range
...