IEC TS 63444:2023

IEC TS 63444 ®
Edition 1.0 2023-11
TECHNICAL
SPECIFICATION
Industrial networks – Ethernet-APL port profile specification
IEC TS 63444:2023-11(en)
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IEC TS 63444 ®
Edition 1.0 2023-11
TECHNICAL
SPECIFICATION
Industrial networks – Ethernet-APL port profile specification
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240 ISBN 978-2-8322-7821-5
– 2 – IEC TS 63444:2023 © IEC 2023
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, abbreviated terms and acronyms . 8
3.1 Terms and definitions . 8
3.2 Abbreviated terms, symbols and acronyms . 10
4 APL overview . 11
4.1 General . 11
4.2 APL relationship to IEEE Std 802.3-2022 and 10BASE-T1L . 14
4.3 Conformance test requirements . 15
5 Port classification . 15
5.1 Overview. 15
5.2 Segment class . 16
5.3 Port class . 16
5.4 Power class . 17
5.5 Intrinsically safe protection class . 22
5.5.1 General . 22
5.5.2 Intrinsically safe concept . 23
6 General port requirements . 24
6.1 Terminals and connectors . 24
6.2 Cable shield termination . 24
6.3 Polarity sensitivity . 25
6.4 Electrical isolation . 25
6.5 Short circuit behavior . 26
7 Network configuration rules . 26
7.1 Segment components . 26
7.2 Topology . 26
7.3 Cables . 26
7.3.1 General . 26
7.3.2 Cable category system . 27
7.3.3 Cables for use in intrinsically safe installations . 28
7.4 Wiring rules . 28
7.5 APL segment definition . 28
8 Electromagnetic compatibility . 28
Annex A (normative) Connectors . 29
A.1 General . 29
A.2 M8 / M12 connectors. 30
A.2.1 General . 30
A.2.2 Requirements . 30
A.2.3 Pin assignment . 30
A.3 PCB and modular terminal blocks . 31
A.3.1 General . 31
A.3.2 Requirements . 31
A.3.3 Pin assignment . 32
A.4 Junction terminal blocks . 33

A.4.1 General . 33
A.4.2 Requirements . 33
A.4.3 Pin assignment . 33
Annex B (normative) Auxiliary devices . 34
B.1 General requirements . 34
B.2 Surge protection . 34
Bibliography . 36

Figure 1 – APL topology example . 11
Figure 2 – Example APL segment including auxiliary devices and inline terminals . 13
Figure 3 – Port classes and related options . 16
Figure 4 – Powered trunk segments with cascade ports . 17
Figure 5 – Example of port class matching between source and load . 18
Figure 6 – Illustrative current step characteristics during start-up of a load port . 22
Figure 7 – Example of intrinsically safe protection class matching to port class and
power class . 23
Figure 8 – Cable shield grounding options . 25
Figure A.1 – Port class to connector type matching . 30
Figure A.2 – Pin assignment of the plug and socket M8 A-coding connectors . 31
Figure A.3 – Pin assignment of the plug and socket M12 A-coding connectors . 31
Figure A.4 – Examples of modular pluggable terminal blocks . 33
Figure A.5 – Representative junction terminal block . 33
Figure B.1 – Basic circuit diagram of coordination between surge protector and
powered APL port . 34
Figure B.2 – Parallel connection of an SPD to an APL segment . 35

Table 1 – IEEE Std 802.3-2022 PHY, management and power options . 14
Table 2 – Segment class . 16
Table 3 – Port classes . 17
Table 4 – Power classes . 18
Table 5 – Electrical characteristics of power classes . 19
Table 6 – Electrical characteristics for trunk ports . 19
Table 7 – Electrical characteristics for spur ports . 21
Table 8 – Intrinsically safe protection class . 23
Table 9 – Minimum required shielding options of a port . 24
Table 10 – Polarity sensitivity . 25
Table 11 – Cable category system . 27
Table A.1 – Supported terminal block / connector types . 29
Table A.2 – Electrical requirements terminal block / connector . 29
Table A.3 – Pin assignments for plug and socket M8 / M12 A-coding connectors . 31
Table A.4 – Pin assignments for 3 position terminal blocks . 32
Table A.5 – Pin assignments for 4 position terminal blocks . 32
Table A.6 – Pin assignments for 6 position terminal blocks . 32

– 4 – IEC TS 63444:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL NETWORKS –
Ethernet-APL port profile specification

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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
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shall not be held responsible for identifying any or all such patent rights.
IEC TS 63444 has been prepared by subcommittee 65C: Industrial networks, of IEC technical
committee 65: Industrial-process measurement, control and automation. It is a Technical
Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
65C/1250/DTS 65C/1275/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – IEC TS 63444:2023 © IEC 2023
INTRODUCTION
TM
IEEE Std 802.3 -2022, Clause 146 specifies the Ethernet Physical Layer 10BASE-T1L,
suitable to be used for full-duplex communication over a single balanced pair of conductors.
This physical layer is specifically designed for industrial applications, supporting the main
requirements for advanced, robust process control and monitoring in safe or hazardous areas.
The primary physical layer solution focuses on four requirements:
• support of single pair cables providing both communication and optional power;
• increased data bandwidth, 10 Mbit/s;
• support of extended Ethernet cable length of up to 1 km;
• support of intrinsically safe protection for use in hazardous areas.
IEEE Std 802.3-2022, Clause 146 only specifies the digital communication method and its
electrical characteristics. To assure interoperability between the various interconnected
components at different parts of the network, applying this new physical layer for industrial
applications requires a further set of specifications and classifications. The "Ethernet Advanced
Physical Layer" (Ethernet-APL or APL) references and standardizes industrial automation
extensions.
This document specifies port profiles for use in non-hazardous and hazardous areas, with and
without power. Ethernet-APL intrinsically safe profiles facilitate the examination of the
interconnection of different Ethernet-APL ports. Most common industrial rated connectors for
use in process industries are part of this document. A multi-length cable category system
maintains communication integrity, while permitting cable constructions optimized for specific
applications or environmental ratings.
Ethernet-APL impacts the various physical layers in IEC 61158-2 and its associated Types. This
document provides a neutral approach for the new advanced physical layer which can be then
transferred to the next editions of different IEC intrinsically safe fieldbus documents. The
following documents are representative of potentially affected next editions: IEC 61158-2,
IEC 61784-1 series, IEC 61784-2 series, IEC 61918, IEC 61784-5 series.
This document is not intended to assure interoperability at the product level but only at the port
level. No reference is made to any Ethernet-based communication protocol above the physical
layer.
INDUSTRIAL NETWORKS –
Ethernet-APL port profile specification

1 Scope
This document is applicable to process automation equipment using a 10BASE-T1L compliant
(see IEEE Std 802.3-2022, Clause 146) Physical Layer (PHY). Ethernet-APL intrinsically safe
profiles with different predefined entity or limitation parameters (for example voltage, current,
power, capacitance, inductance, cable length) simplify the examination of the interconnection
of different Ethernet-APL ports.
The following technical features are part of this document:
• topology with trunk/spur installation capability;
• 2-wire technology (full-duplex communication data rate of 10 Mbit/s);
• long distance (refers to cable lengths of several hundred meters, with spans up to 1 000 m);
• intrinsic safety (installation of Ethernet-capable field devices in hazardous areas);
• power supply to field devices over the same 2-wire cable used for data communication.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
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
IEC TS 60079-47:2021, Explosive atmospheres – Part 47: Equipment protection by 2-wire
intrinsically safe ethernet concept (2-WISE)
IEC 61010-1, Safety requirements for electrical equipment for measurement, control, and
laboratory use – Part 1: General requirements
IEC 61076-2-101, Connectors for electronic equipment – Product requirements – Part 2-101:
Circular connectors – Detail specification for circular connectors for M12 connectors with screw-
locking
IEC 61076-2-104, Connectors for electronic equipment – Product requirements – Part 2-104:
Circular connectors – Detail specification for circular connectors with M8 screw-locking or snap-
locking
IEC 61158-2:2023, Industrial communication networks – Fieldbus specifications – Part 2:
Physical layer specification and service definition
IEC 61643-21, Low voltage surge protective devices − Surge protective devices connected to
telecommunications and signalling networks – Performance requirements and testing methods

– 8 – IEC TS 63444:2023 © IEC 2023
IEEE Std 802.3-2022, IEEE Standard for Ethernet
ASTM D4566-05, Standard Test Methods for Electrical Performance Properties of Insulations
and Jackets for Telecommunications Wire and Cable; available at < ASTM D4566-05 - Standard
Test Methods for Electrical Performance Properties of Insulations and Jackets for
Telecommunications Wire and Cable (ansi.org)> [viewed 2023-10-13]
3 Terms, definitions, abbreviated terms and acronyms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1.1
Advanced Physical Layer
APL
physical layer based on 10BASE-T1L according to IEEE Std 802.3-2022 with additional optional
features like intrinsic safety, power over 2 wires
Note 1 to entry: Additional requirements for use in process industries are specified in this document.
3.1.2
APL segment
segment that consists of two APL ports, each containing a 10BASE-T1L compatible PHY,
connected at each end of a two-wire, shielded cable
Note 1 to entry: An APL segment can optionally be equipped with a maximum of two auxiliary devices and can
contain up to 10 inline terminal connections. An auxiliary device corresponds to one inline connection; for example,
having two auxiliary device connected to one APL segment will reduce the number of inline connections by two.
Note 2 to entry: An APL segment is either a trunk or a spur.
3.1.3
APL switch
Ethernet switch including at least one APL compliant port
3.1.4
APL port
electrical and mechanical interface of a device to an APL segment
3.1.5
auxiliary device
device, which is connected within an APL segment and does not include a 10BASE-T1L PHY
Note 1 to entry: Auxiliary devices are defined in Annex B.
Note 2 to entry: An auxiliary device can comprise a power load or introduce communication signal insertion losses.
EXAMPLE A surge protector is an example of an auxiliary device.
3.1.6
cable stub
unterminated branch of the segment cable

3.1.7
cascade port
APL port used in powered daisy chain networks
Note 1 to entry: If the cascade port is used in a powered ring network it shall be either a power source port or a
power load port depending on the status of the ring.
3.1.8
inline connection
mated device or combination of devices, including terminations used to connect cables or cable
elements to other cables or application specific equipment
3.1.9
current event
change of load current during power-up sequence with a specific characteristic
Note 1 to entry: A current event could be either a current step or a current spike.
3.1.10
field switch
APL switch having at least one port to which a spur can be connected
3.1.11
port
interface between a device and an APL segment
3.1.12
port class
port powering characteristics
3.1.13
power switch
APL switch including at least one port feeding power into a trunk
3.1.14
PHY
physical layer circuitry required to implement physical layer functions
3.1.15
overcurrent condition
condition when a power load port draws more than the minimum continuously provided current
I of the power source port
PS(min)
3.1.16
spur
 segment which connects a field device to a field switch
3.1.17
segment
point-to-point connection between two APL ports
3.1.18
surge protective device
SPD
electrical device that is used to protect electronic equipment against electrical surges and
voltage spikes
Note 1 to entry: A SPD is an auxiliary device.

– 10 – IEC TS 63444:2023 © IEC 2023
3.1.19
trunk
 segment which connects a power switch to a field switch or a field switch to a field
switch
3.1.20
2-WISE
2-Wire intrinsically safe Ethernet concept based on APL with standardized limits for intrinsic
safety parameters, designed to simplify the examination process for components and cable
parameters within APL segments
[SOURCE: IEC TS 60079-47:2021, 3.3, modified − a new term has been assigned.]
3.1.21
operating mode
2.4 V
pp
10BASE-T1L compliant operating mode with a signal amplitude of 2,4 V
pp
Note 1 to entry: This mode is used on APL trunk segments.
3.1.22
1.0 V operating mode
pp
10BASE-T1L operating mode with a signal amplitude of 1,0 V
pp
Note 1 to entry: This mode is used on APL spur segments.
3.2 Abbreviated terms, symbols and acronyms
C unlimited input capacitance of a load port
in
E initial inrush energy of a load port or cascade port during power-up, caused by
in
charging-up its input capacitance
EMC electromagnetic compatibility
Ex indicates that the electrical equipment corresponds to one or more of the types
of protection which are subject of the standards IEC 60079-0 or IEC 60079-11
I maximum current during a current spike event of a load port during start-up
CSp(max)
I minimum continuously provided current at the power source terminals except
PS(min)
during inrush or an overcurrent condition
I minimum consumed current at the power load terminals except during inrush or
PL(min)
an overcurrent condition
maximum consumed current at the power load terminals during an under voltage
I
PL(max)
condition
I reverse current for polarity sensitive power load ports
PL(reverse)
P minimum available power at the power load terminals
PL(min)
P minimum available output power at the power source terminals
PS(min)
PSANEXT power sum alien near end crosstalk loss

PSAFEXT power sum alien far end crosstalk loss

Q electric charge during a current spike event for a load port during power-up
CSp
R internal resistance of a power source port
out
maximum allowed voltage at the power source terminals over the full range of
U
PS(max)
operating conditions
U minimum available output voltage at the power source terminals over the full
PS(min)
range of operation conditions
U minimum available voltage at the power load terminals
PL(min)
4 APL overview
4.1 General
APL has been specifically designed to modernise digital instrumentation solutions used for
industrial process control, offering enhanced features of communication, powering and device
control in between Zone 2, 1 and 0, or Zone 20, 21 and 22.
Figure 1 illustrates an example of an APL network connected to a control network. The
communication link between the control network and the APL segment is performed through a
power switch, which additionally feeds power onto the APL trunk. A field switch is connected to
the opposite end of the APL trunk, which is powered by the trunk, whereon it feeds the power
to each spur port and to a second trunk port. The second trunk port provides a new powered
trunk segment for a second field switch and so on. Each spur port finally terminates at a field
device, which may also be powered in accordance with the applicable hazardous area
classification. Field devices, which shall be intrinsically safe certified, can be located within any
rated hazardous area. The number of cascaded field switches is limited because of the available
power. To calculate the number of cascaded field switches, the following applies: the output
power of the source port is the input power of the load port minus the power consumption of the
device and minus the internal losses.
It is strongly recommended to maintain cable type continuity in an APL segment as to minimize
the effect of insertion and return loss.

Figure 1 – APL topology example
An APL trunk shall be conformant to IEEE Std 802.3-2022, Clause 146, 10BASE-T1L link
segment definition in "2.4 V operating mode" and an APL spur shall comply with
pp
IEEE Std 802.3-2022, Clause 146, 10BASE-T1L link segment definition in "1.0 V operating
pp
mode". An APL segment can comprise either a trunk or a spur.

– 12 – IEC TS 63444:2023 © IEC 2023
As shown in Figure 2, an APL segment comprises two ports connected to each end of a trunk
or spur cable, with auxiliary devices and terminal blocks or connectors in between. A spur
always ends at a field device. The cable, optional auxiliary devices and junction terminals are
defined within this specification.
For powered segments, one source port provides power into the segment, and the load port or
the auxiliary device consumes power from the segment.
For use in hazardous areas according to IEC 60079-14, in which intrinsically safe rated circuits
are required, the ports can be classified as intrinsically safe according to level of protection ia,
ib, ic.
NOTE A particular national or regional standard, code or directive could use other particular notations, differing
from international IEC notations.
Different terminal blocks are supported with terminal options as screw-type or spring-force-type.

NOTE 1 Auxiliary devices can cause additional insertion loss for example by integrated inline resistors.
NOTE 2 An auxiliary device, typically a surge protector, does not contain a PHY.
Figure 2 – Example APL segment including auxiliary devices and inline terminals

– 14 – IEC TS 63444:2023 © IEC 2023
4.2 APL relationship to IEEE Std 802.3-2022 and 10BASE-T1L
APL is based on the 10BASE-T1L physical layer (PHY) specification of IEEE Std 802.3-2022,
Clause 146. APL specifies the application of 10BASE-T1L to industry sectors, particularly to
process industries.
APL is compatible with 10BASE-T1L, but limits PHY options to suit the intended applications.
Table 1 defines the APL option support.
Table 1 – IEEE Std 802.3-2022 PHY, management and power options
PHY option Description Reference in APL support
IEEE Std 802.3-2022
PCS Physical coding sublayer 146.3 Required
PMA Physical medium attachment, 10BASE-T1L 146.4 Required
AN Auto-Negotiation Clause 98 Required
LSM Low speed mode 98.5.6 Required
10T1L 10BASE-T1L Clause 98, Clause 146 Required
a
Energy efficient Ethernet (EEE) capability Clause 78, 146.1.2 Prohibited
EEE
RTDL 2.4 V operating mode 146.5.4.1 Conditional
pp
b
PSETE 104.1.3 Prohibited
Power over data lines (PoDL ) of single balanced
twisted-pair Ethernet, PSE type E for 10BASE-
T1L
b
PDTE 104.1.3 Prohibited
Power over Data Lines (PoDL ) of single balanced
twisted-pair Ethernet, PD Type E for 10BASE-T1L
c
MDI line powering voltage tolerance 146.8.5 Prohibited
MDI4
d
Installation / cabling 146.7 See 7.5
*INS
a
EEE can interfere with low latency applications and disturb power distribution. EEE can be implemented in a
PHY but disabled.
b
PoDL for 10BASE-T1L does not provide an intrinsic safety capability. PoDL for 10BASE-T1L does not provide
cascade operation capability.
c
MDI4 is related to PoDL enabled ports. APL power concepts require lower voltage levels due to hazardous
area use and dedicated safety concepts avoiding hazardous situation if applying higher voltages to a port. A
port can be damaged by blowing an internal non-replaceable fuse.
d
The asterisk character "*" in front of an item name like "*INS" is a syntax element specified in
IEEE Std 802.3-2022, 8.8.3.4 saying: "Each item whose reference is used in a conditional symbol is indicated
by an asterisk in the Item column."

The equivalent of the Ethernet MDI is an APL connector or terminal block as defined in Annex A.
A trunk port shall only operate in 2.4 V operating mode.
pp
A trunk port shall not enable communication but can still link up when the connected port at the
far end tries to establish a link with a transmit voltage other than 2,4 V .
pp
A spur port shall only operate in 1.0 V operating mode.
pp
A spur port shall not enable communication, but can still link up, when the connected port at
the far end tries to establish a link with a transmit voltage other than 1,0 V .
pp
As APL ports shall have Auto-Negotiation enabled, the transmit amplitude shall be fixed by
setting the IEEE Std 802.3-2022, Clause 98 Auto-Negotiation Technology Ability Field Bits A23

(10BASE-T1L increased transmit level request) and A24 (10BASE-T1L increased transmit /
receive level ability) for a trunk port to 1 and for a spur port to 0.
Additionally in the IEEE Std 802.3-2022, Clause 98, Auto-Negotiation Technology Field Bit A9
(10BASE-T1L capability) shall be set to 1 and all other bits besides A23 and A24, which shall
be set to support the correct transmit amplitude, shall be set to zero.
Additional requirements for APL conformance tests are provided in 4.3.
4.3 Conformance test requirements
IEEE Std 802.3-2022, 146.5.4.2, defines a maximum droop of 10 % when running the
10BASE-T1L PHY in test mode 2 and driving into a 100 Ω external termination. Performing APL
conformance tests, an additional power coupling network could be required during these tests
utilizing a 1 mH inductor and a 100 Ω in series with 0,5 µF termination impedance. Based on
this power and termination network, the overall droop could be higher than 10 %. An APL port
conforming to the APL port profile specification shall not produce a droop higher than 13 %
when being tested in combination with the above mentioned power coupling network. Including
measurement tolerances during the conformance test, the measured droop shall not be higher
than 15 %. The droop is measured between 400 ns and 1 066,7 ns after the zero crossing. To
reduce the influence of measurement noise, the bandwidth of the droop measurement should
be not greater than 20 MHz. This can be achieved by post processing (e.g. time-averaging)
higher bandwidth samples. If the observed waveform differs substantially from the expected
trapezoidal waveform with exponential droop, then the first measurement point should be taken
at the (smoothed) peak, with the second measurement 666,7 ns later.
An APL port shall be able to withstand a peak-to-peak signal amplitude of up to 1,55 V without
pp
causing a transmit distortion of more than 50 mV .
pp
The time between activating the Auto-Negotiation process between two ports and the
established communication link shall take maximum 7 s.
5 Port classification
5.1 Overview
Ports are classified by different classes which determine the interoperability between two ports.
The port classification scheme is illustrated in Figure 3. For each port class, several options
are defined. Not all combinations of options are permitted. Allowed combinations of options are
specified in the respective port class subclauses.
The intrinsically safe protection classes are listed in Table 8 for more information.

– 16 – IEC TS 63444:2023 © IEC 2023

Figure 3 – Port classes and related options
5.2 Segment class
Table 2 specifies the segment classes. The APL segment class defines the type of supported
segments specified in IEEE Std 802.3-2022, Clause 146.
Table 2 – Segment class
Segment 10BASE-T1L Supported Maximum Maximum number of inline connections
class operating cable length number of in an APL segment
mode auxiliary devices
m
S Spur 1.0 V 0 to 200 2 4
pp
T Trunk 2.4 V 0 to 1 000 2 10
pp
Maximum number of inline connections does not include cable terminations of the APL ports.
An auxiliary device corresponds to one inline connection; for example, having two auxiliary device connected to
one APL segment reduces the number of inline connections by two.
Auxiliary devices, having inline resistance, reduces the supported cable length in powered APL segments due to
the additional voltage drop and insertion loss.

5.3 Port class
The port class defines the port powering characteristics.
Table 3 summarizes the different port classes and the permitted combinations of port classes
used to form an APL segment.
Table 3 – Port classes
Port class Permitted combinations
P Power source port provides power to a power load port. P-L, P-C
L
L Power load port requires power from a power source port. P-L, C -L
P
C Powered port which can be power source (C ) or power load port (C ). P-C , C -L, C -C
P L L P P L
Cascade ports can be used in a powered ring or in a powered daisy chain
configuration. A cascade port feeding power (C ) receives its power from a
P
cascade port operating as a load port (C ) in the same device. The cascade
L
load port (C ) in turn is connected to either a power source port (P) or to
L
another cascade port operating as a source port (C ) in a different device.
P
See Figure 4.
If a port class C is connected to a port class P port, the C port shall remain passive (C ) and shall not feed any
L
power into the APL segment.
A cascade source port (C ) powered by a cascade load port (C ) can have reduced output values. The output
P L
power of the source port (C ) is the input power of the load port (C ) minus the power consumption of the device
P L
and minus the internal losses.
Cascade ports are only permitted on the trunk.
NOTE Powered ring topology is out of scope of the port profile specification. To support a powered ring topology
in a future revision of this document, additional port classes will need to be added. A passive cascade port class
implementations does not necessarily support future active ring configurations.

Figure 4 shows a trunk topology with cascaded field switches.

Figure 4 – Powered trunk segments with cascade ports
5.4 Power class
The electrical characteristics of power source ports "P", power load ports "L" and cascade ports
"C" are categorized by their power class. Power classes A and C shall be used for intrinsically
safe rated spur ports intended to be used primarily in hazardous area applications. Power class
3 is intended to be used for non-intrinsically safe rated trunk ports.
Table 4 defines the permitted combinations of segment classes, port classes and power
classes.
– 18 – IEC TS 63444:2023 © IEC 2023
Table 4 – Power classes
Source power Maximum voltage / Permitted segment Permitted port Permitted load
class minimum output classes classes power classes
power
A 15 V DC / 0,54 W S P, L A
C 15 V DC / 1,11 W S P, L A, C
3 50 V DC / 57,5 W T P, L, C 3
4 50 V DC / 92 W T P, L, C 3, 4

Combination of classes other than those given in Table 4 are prohibited. The permitted
combinations of port classes do not imply that every combination is also permitted from an
intrinsically safe viewpoint.
A load port can be specified for more than one load power class.
Cascade (C) ports can only be connected to a power source port having equal or lower
maximum output values (voltage, current and power) than the input values specified for the
cascade port.
Figure 5 provides an example of power class matching. A field device port with classification
SLAA can be connected either to a field switch port with classification SPAA or SPCC.

Figure 5 – Example of port class matching between source and load
Table 5 shows the power class requirements.

Table 5 – Electrical characteristics of power classes
Power class
Parameter
A C 3 4
f f d d
U (V DC)
15 15 50 50
PS(max)
g g
U (V DC) 9,6 11,61
46 46
PS(min)
g g
I (mA) 55,56 95
1 250 2 000
PS(min)
g g
P (W) 0,54 1,1
57,5 92
PS(min)
b b c c
U (V DC)
9,0 10,6 28,8 28,8
PL(min)
a b b c, h c, h
P (W) 0,5 1,0 36 57,6
PL(min)
e
I (mA) 20
PL(min)
j
I (mA)
See footnote
PL(max)
i
I (mA) Not applicable
≤ 10
PL(reverse)
NOTE 1 U and U are specified for steady state operation without communication voltage.
PS(max) PS(min)
NOTE 2 All parameters in Table 5 reflect the electrical DC characteristics. The communication signal is added
as an additional signal source to the DC electrical parameters.
a
P is the product of the minimum continuously provided current I and the minimum available voltage
PL(min) PS(min)
U .
PL(min)
b
U and P are determined by cable losses due to the wire resistance of AWG 18 cable with a length
PL(min) PL(min)
of 200 m at a wire temperature of 70 °C (equivalent to 10,6 Ω loop resistance) at maximum load.
c
Calculation is required, considering load condition and the cable resistance at the maximum wire temperature,
to guarantee U and P .
PL(min) PL(min)
d
U shall be
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