EN IEC 63257:2026

• Abstract:

  IEC 63257:2026 applies to photovoltaic (PV) system components and communication networks supporting the communication of the DC shutdown equipment using power line communication. This document defines how to propagate the operational state of the entire PV system (normal / shutdown) to the individual power production components comprising the PV system. The document also describes requirements and constraints associated with power line communication networks that are used to support this application. This document defines the communication requirements for reducing the output voltage of the DC cables that leave a PV array. This output voltage reduction function can support emergency responders during firefighting operations. For this function, communication is necessary from the inverter / initiator to the PV-modules.

• Status: Published
• Publication Date: 02-Jul-2026
• ICS: 27.160 - Solar energy engineering
• Technical Committee: CLC/TC 82 - Solar photovoltaic energy systems
• Drafting Committee: IEC/TC 82 - IEC_TC_82
• Current Stage: 6060 - Document made available - Publishing
• Start Date: 03-Jul-2026
• Due Date: 31-Dec-2021
• Completion Date: 03-Jul-2026
• Ref Project: SIST EN IEC 63257:2026 - Power line communication for DC shutdown equipment - Communication signal, physical layer (IEC 63257:2026)

• Refers: IEC TS 61836:2016 - Solar photovoltaic energy systems - Terms, definitions and symbols
• Effective Date: 16-Jun-2026
• Refers: IEC 62548:2016 - Photovoltaic (PV) arrays - Design requirements
• Effective Date: 16-Jun-2026
• Refers: EN 55011:2016 - Industrial, scientific and medical equipment - Radio-frequency disturbance characteristics - Limits and methods of measurement
• Effective Date: 16-Jun-2026
• Refers: EN 55011:2016/A2:2021 - Industrial, scientific and medical equipment - Radio-frequency disturbance characteristics - Limits and methods of measurement
• Effective Date: 16-Jun-2026
• Refers: EN 55011:2016/A1:2017 - Industrial, scientific and medical equipment - Radio-frequency disturbance characteristics - Limits and methods of measurement
• Effective Date: 16-Jun-2026

SLOVENSKI STANDARD
01-december-2026
Komunikacije po energetskih vodih za izklop enosmerne opreme - Komunikacijski
signal, fizikalna raven (IEC 63257:2026)
Power line communication for DC shutdown equipment - Communication signal, physical
layer (IEC 63257:2026)
Powerline-Kommunikation für DC-Abschalteinrichtungen - Kommunikationssignal,
physikalische Schicht (IEC 63257:2026)
Communication de ligne électrique pour les équipements d’arrêt du courant continu -
Signaux de communication, couche physique (IEC 63257:2026)
Ta slovenski standard je istoveten z: EN IEC 63257:2026
ICS:
27.160 Sončna energija Solar energy engineering
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 63257

NORME EUROPÉENNE
EUROPÄISCHE NORM July 2026
ICS 27.160
English Version
Power line communication for DC shutdown equipment -
Communication signal, physical layer
(IEC 63257:2026)
Communication de ligne électrique pour les équipements Powerline-Kommunikation für DC-Abschalteinrichtungen -
d'arrêt du courant continu - Signaux de communication, Kommunikationssignal, physikalische Schicht
couche physique (IEC 63257:2026)
(IEC 63257:2026)
This European Standard was approved by CENELEC on 2026-06-10. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 63257:2026 E
European foreword
The text of document 82/2189/FDIS, future edition 1 of IEC 63257, prepared by TC 82 "Solar
photovoltaic energy systems" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN IEC 63257:2026.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2027-07-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2029-07-31
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 63257:2026 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 63027 NOTE Approved as EN IEC 63027
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 62548 2016 Photovoltaic (PV) arrays - Design - -
requirements
IEC/TS 61836 - Solar photovoltaic energy systems - - -
Terms, definitions and symbols
CISPR 11 2015 Industrial, scientific and medical equipment EN 55011 2016
- Radio-frequency disturbance
characteristics - Limits and methods of
measurement
+ A1 2016 + A1 2017
- - + A11 2020
+ A2 2019 + A2 2021
IEC 63257 ®
Edition 1.0 2026-05
INTERNATIONAL
STANDARD
Power line communication for DC shutdown equipment - Communication signal,
physical layer
ICS 27.160  ISBN 978-2-8327-1161-3

IEC 63257:2026-05(en)
IEC 63257:2026 © IEC 2026
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms. 9
4 Power line communication systems . 9
4.1 General history of PLC . 9
4.2 PLC operational considerations . 9
5 DC shutdown system configuration . 9
5.1 General . 9
5.2 System setup . 10
5.3 Operational considerations . 10
6 Operating modes . 10
6.1 General . 10
6.2 Active mode . 10
6.3 Shutdown mode . 10
6.4 Standby signal . 11
6.5 Mode transitions . 11
7 Power line communication requirements . 12
7.1 Crosstalk . 12
7.2 Crosstalk mitigation . 12
7.2.1 General. 12
7.2.2 Physical crosstalk mitigation . 13
7.3 Physical layer aspects . 13
7.4 Transmitter . 13
7.4.1 General. 13
7.4.2 Requirements for the transmitter . 14
7.4.3 Transmitter out-of-band emission requirements . 14
7.4.4 Transmitter in-band emission requirements. 15
7.5 Receiver . 16
7.5.1 General. 16
7.5.2 Requirements for the receiver . 16
7.6 Protocol . 18
8 Summary . 20
Annex A (informative) Standby signal . 21
A.1 General . 21
A.2 Reduced power consumption during the night . 21
A.3 Ease of installation . 21
Annex B (informative) Arc fault detector compatibility . 22
Annex C (normative) Multi-module shutdown device . 23
Annex D (informative) PV system configuration limits for the provided power line
communication values . 24
Annex E (informative) PV installation best practices . 25
IEC 63257:2026 © IEC 2026
Annex F (normative) Test specification . 28
F.1 General . 28
F.2 Transmitter electrical test specification . 28
F.2.1 Principle of transmitter electrical test . 28
F.2.2 Transmitter electrical performance test. 29
F.3 Receiver electrical test specification . 34
F.3.1 Principle of receiver test . 34
F.3.2 Receiver electrical performance tests . 37
F.4 Equipment interoperability test specification . 48
F.4.1 Technical interoperability definition . 48
F.4.2 Prerequisites to interoperability tests . 48
F.4.3 Symptoms of interoperability and non-interoperability . 49
F.4.4 Overall interoperability test framework . 50
F.5 Interoperability test sequences . 51
F.5.1 Start process interoperability test: single receiver . 51
F.5.2 Stop process interoperability test: single receiver . 52
F.5.3 Repeated start and stop interoperability test: single receiver . 53
F.5.4 Multiple receiver interoperability test: . 54
Bibliography . 56

Figure 1 – Example of DC shutdown system . 10
Figure 2 – Stop process timing. 11
Figure 3 – Start process timing . 12
Figure 4 – Capacitive and inductive coupling . 12
Figure 5 – Example of string cabling . 13
Figure 6 – Out-of-band spectrum mask . 15
Figure 7 – In-band spectral mask . 16
Figure 8 – Rejection ratio graph . 17
Figure 9 – In-band rejection graph . 18
Figure 10 – Keep Alive duty cycle timing diagram . 19
Figure E.1 – String combiner box . 25
Figure E.2 – Example of good string combiner wiring . 26
Figure E.3 – Example of roof installation . 27
Figure F.1 – Transmitter test configuration . 29
Figure F.2 – Test of frequency accuracy . 29
Figure F.3 – Test of signal timing accuracy . 30
Figure F.4 – Transmitter output level test . 32
Figure F.5 – Transmitter in band spurious emission mask . 33
Figure F.6 – Schematic for in band and out of band test . 33
Figure F.7 – Transmitter out of band spurious emission mask . 34
Figure F.8 – Receiver test configuration in case of a single module SD . 35
Figure F.9 – Receiver test configuration in case of a multi module SD . 36
Figure F.10 – Optional use of R and L . 36
M 1
Figure F.11 – IEC SD PLC signal . 39
Figure F.12 – In-band interferer rejection test levels (RMS) . 41
IEC 63257:2026 © IEC 2026
Figure F.13 – Out-of-band interferer rejection test levels . 43
Figure F.14 – Power line communication with superimposed CW signal . 46
Figure F.15 – Test setup . 47
Figure F.16 – Principle of communication interoperability test framework . 51
Figure F.17 – Start process interoperability test timing . 52
Figure F.18 – Stop process interoperability test timing . 53
Figure F.19 – Repeated start and stop process interoperability test timing. 54
Figure F.20 – Multiple receiver interoperability test diagram . 55

Table 1 – Timing requirements for mode transitions . 11
Table 2 – Out-of-band spectral mask parameters . 14
Table 3 – In-band spectral mask parameters . 15
Table 4 – Rejection ratio values . 17
Table 5 – In-band rejection values . 18
Table 6 – Physical layer parameters . 19
Table A.1 – Standby signal . 21
Table F.1 – Frequency accuracy . 29
Table F.2 – Transmitter output level and output impedance test . 32
Table F.3 – Receiver test equipment components . 37
Table F.4 – In-band interferer frequency and signal levels . 41
Table F.5 – Out-of-band interferer frequency signal levels . 42
Table F.6 – Example of a list of interoperable equipment compatible with the IEC DC-
shutdown specification . 48
Table F.7 – Start process interoperability test steps . 51
Table F.8 – Stop process interoperability test steps . 52
Table F.9 – Repeated start and stop process interoperability test steps . 54

IEC 63257:2026 © IEC 2026
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Power line communication for DC shutdown
equipment - Communication signal, physical layer
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, Technical Reports,
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by 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
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
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6) All users should ensure that they have the latest edition of this publication.
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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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 63257 has been prepared by IEC technical committee 82: Solar photovoltaic energy
systems. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
82/2189/FDIS 82/2593/RVD
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 International Standard is English.
IEC 63257:2026 © IEC 2026
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, or
– revised.
IEC 63257:2026 © IEC 2026
INTRODUCTION
This document defines the communication requirements for reducing the output voltage of the
DC cables that leave a PV array. This output voltage reduction function can support emergency
responders during firefighting operations. For this function, communication is necessary from
the inverter / initiator to the PV-modules. Today there are many ways to accomplish this
communication task and it is possible to use either wired or wireless solutions. With wireless
solutions issues with range and/or communication robustness may occur. Although robustness
can be tackled with protocols and modulation schemes, it is sometimes hard to get the
necessary range due to physical limitations and normative regulations. With wired
communication the need of an additional wire which has to be installed along with the DC power
cabling is often a problem. A solution for this is to use power line communication so that the
DC power and the information signal are on the same cable and therefore installation
requirements and costs are low because the necessity of laying an extra communication cable
is eliminated. This document has been developed to set rules for such a power line
communication.
IEC 63257:2026 © IEC 2026
1 Scope
This document applies to photovoltaic (PV) system components and communication networks
supporting the communication of the DC shutdown equipment using power line communication.
This document defines how to propagate the operational state of the entire PV system (normal
/ shutdown) to the individual power production components comprising the PV system. The
document also describes requirements and constraints associated with power line
communication networks that are used to support this application.
NOTE 1 It is possible to have systems communicating in different ways to the method covered in this document.
E.g., in systems where all components of the PLC communication are from the same manufacturer. For those systems
this document does not apply.
NOTE 2 Not included in the scope of this document are requirements for DC shutdown initiator mechanism,
disconnection and de-energization.
NOTE 3 This document does not address whether DC shutdown is required or not.
NOTE 4 EMC requirements are not included in this document.
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 TS 61836, Solar photovoltaic energy systems - Terms, definitions and symbols
IEC 62548:2016, Photovoltaic (PV) arrays - Design requirements
CISPR 11:2015, Industrial, scientific and medical equipment - Radio-frequency disturbance
characteristics - Limits and methods of measurement
CISPR 11:2015/AMD1:2016
CISPR 11:2015/AMD2:2019
3 Terms, definitions and abbreviated terms
For the purposes of this document, the terms and definitions given in IEC TS 61836 and the
following 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 Terms and definitions
3.1.1
components
equipment intended to be used in a DC shutdown system to initiate, disconnect or isolate the
controlled conductors of a PV system
3.1.2
communication protocol
formal descriptions of digital message formats and rules
IEC 63257:2026 © IEC 2026
3.1.3
initiation device
initiator
manual or automatic switching device, input port or signal that will result in the activation of the
shutdown system function(s)
3.1.4
PV power source
DC array or aggregate of arrays that generates DC power
3.1.5
receiver
equipment responsible for accepting the communication signal sent by a transmitter and
capable of initiating a state change of PV power source components based on the signal
received (see 5.2)
3.1.6
shutdown function
function that reduces the output voltage of the DC cables leaving a PV array in a certain amount
of time
3.1.7
DC shutdown system
components and communication protocols that are used to perform shutdown function.
Components of a shutdown communication system are initiator(s), transmitter(s), and
receiver(s)
3.1.8
transmitter
equipment responsible for sending a communication signal that reflects the current state of the
initiation device (see 5.2)
3.1.9
barker code
finite sequence of digital values with ideal autocorrelation property used for synchronization in
digital communication
3.1.10
spread frequency shift keying
S-FSK
frequency modulation scheme which uses discrete frequency changes of a carrier signal to
transmit digital information
Note 1 to entry: The main benefit compared to normal frequency shift keying is that the carrier frequencies are
separated by at least 10 kHz and the receiver only needs one carrier to decode the complete message.
IEC 63257:2026 © IEC 2026
3.2 Abbreviated terms
AFD Arc Fault Detector
AFPE Arc Fault Protection Equipment
MLE Module Level Electronics
MLPE Module Level Power Electronics
MLSD Module Level Shutdown Device
NRZ Non-Return to Zero
PLC Power line Communication
PPM Parts per Million
PS Power Supply
PV Photovoltaic
RCMU Residual Current Monitoring Unit
RMS Root Mean Square
SD Shutdown Device
S-FSK Spread Frequency Shift Keying
SS Shutdown System
4 Power line communication systems
4.1 General history of PLC
Since the beginning of the electrification of households and the industry there has also been
the need for data communication, so power line communication has an over hundred-year
history. It started with ripple control with frequencies ≤ 2 kHz back in the early 1900s to switch
streetlights on and off and is nowadays capable of Gbit/s transmissions with cheap plug-in
adapters that use frequencies from 2 MHz up to 300 MHz for in-home use.
As the calculation power of microprocessors or microcontrollers now reaches levels which were
unimaginable at the beginning of the computer era, we can now have a myriad of carriers each
with different complex modulation schemes and error correcting codes so we can reach the
goal of a transmission system that operates nearly at the Shannon limit (the theoretical
maximum rate of error free data that can be transferred over a given noisy transmission
channel) with very high data rates or very robust data transmission.
4.2 PLC operational considerations
Interoperability and safety are the main goals of this document, but also unnecessary human
interaction or complexity is to be avoided if possible.
For this reason, a very common, robust and easy modulation technique, spread frequency shift
keying (S-FSK) is used. Additionally, Barker codes ensure robustness against noise and false
signal detection.
5 DC shutdown system configuration
5.1 General
A DC shutdown system comprises components and communication protocols to perform
shutdown function. See Figure 1. The switches shown in the diagram are just an example of
how the modules can be disconnected.
IEC 63257:2026 © IEC 2026
Figure 1 – Example of DC shutdown system
5.2 System setup
A system shall have at least one initiator and one transmitter and several receivers for the
shutdown signal. The receivers can also incorporate a transmitter for sending status information
back to the inverter / shutdown transmitter. See Annex D for the system boundaries that are the
basis for all the parameter values in this document.
5.3 Operational considerations
Shutdown systems shall provide a mechanism to bring the PV system(s) back online after a
shutdown event.
6 Operating modes
6.1 General
Two modes of operation are defined for a shutdown system: active mode and shutdown mode.
6.2 Active mode
In active mode the system generates power and operates unimpeded by the shutdown system.
This mode is active as long as the initiator is set to “on”. The system shall monitor the Initiator
for a change in operating state. It is activated by periodically sending a ‘permission to operate’
(keep alive) signal.
6.3 Shutdown mode
As the initiator is set to “off” the system shall change into the shutdown mode in a certain
amount of time as specified in Table 1. In shutdown mode the system needs to limit the power
and voltage of the DC system. The change from shutdown mode to active mode shall be done
in a certain amount of time specified as T in Table 1.
Start
IEC 63257:2026 © IEC 2026
6.4 Standby signal
When in shutdown mode each PV-module receiver can output a standby-signal. If a standby
signal is used it shall be a low voltage, low current signal as defined in Annex A.
6.5 Mode transitions
As the PV system has to be de-energized in a certain period of time, e.g. 30 s, each subsystem
has to get a share of the total time to facilitate the process steps needed to do this.
A typical process can be considered as the following sequence of events:
– T : Initiator signals shutdown mode to shutdown transmitter.
– T : Shutdown transmitter stops sending the periodical permission to operate signal.
– T : Receiver / MLE disconnects / de-energizes all PV power sources.
: Stored energy from equipment connected to the DC-lines (e.g., an inverter) is reduced
– T
so a safe voltage level (V ) is reached.
Off
The timing requirements can be found in Table 1 and are depicted in Figure 2 and Figure 3.
Table 1 – Timing requirements for mode transitions
Symbol Mode specification Max. Unit
Time for initiator to relay to transmitter 2 s
T
Time for transmitter to stop sending permission to operate signal 2 s
T
Time for receiver to switch off / de-energize PV power sources 13 s
T
Time for stored energy to be reduced 13 s
T
Total time T + T + T + T 30 s
T
1 2 3 4
T
Time for the MLE to switch on PV power sources 20 s
T
Start
Figure 2 – Stop process timing
IEC 63257:2026 © IEC 2026
Figure 3 – Start process timing
The time from the Initiator sending permission to operate to the transmitter sending the first
keep alive signal (T ) depends on the manufacturers implementation and shall be stated in
MS
the product manual.
7 Power line communication requirements
7.1 Crosstalk
A big challenge in many communication systems, especially with PLC is crosstalk. Crosstalk
means that a (PLC-)signal on one line/wire is influencing a signal/channel on another line/wire
to which it is not galvanically connected. Crosstalk is usually caused by unwanted capacitive
and/or inductive coupling and can lead to deteriorated signal reception or to unwanted
behaviour due to misinterpreted signals. In a PV system it is very common that the DC wires of
the modules are put together in conduits. If there are DC wires from different inverters put
together in one conduit the wires will run in parallel, so crosstalk is inevitable. If a
communication system uses broadcast messages (unaddressed messages) then even
receivers that are not directly connected with the transmitter can receive the broadcasted
message. See Figure 4.
Capacitive coupling Inductive coupling

Figure 4 – Capacitive and inductive coupling
7.2 Crosstalk mitigation
7.2.1 General
There are two ways of coping with crosstalk. Physically, by preventing signal coupling through
shielding and/or better wiring practices or logically by implementing suitable protocols. A
combination of both can be useful.
IEC 63257:2026 © IEC 2026
7.2.2 Physical crosstalk mitigation
It is important that the wiring in the system is done according to applicable safety standards.
By following the rules of IEC 62548:2016, 7.4.3 and the points listed below, the system will be
more robust against overvoltage from indirect lightning, will have lower EMI radiation and have
less crosstalk.
• The DC+ and DC- cables from one string shall be put together as close as possible. This
reduces the loop area and therefore minimizes the unwanted radiation of signals. See
Figure 5.
• Cables going from the inverter to the PV modules shall be placed in a metal conduit that is
connected to earth.
• Cables from different inverters shall be bundled in different conduits.
• Avoid wire loops.
Figure 5 – Example of string cabling
See Annex E for more examples.
7.3 Physical layer aspects
The transmitter uses the DC power lines to transmit a signal to the receivers of the (sub)system.
The transmitter continuously sends a “permission to operate” (“keep alive”) signal if the initiator
is set to “permission to operate”. As long as the receivers get this signal, they are allowed to
put power on the DC lines. When the transmitter ceases to send this “permission to operate”
signal, the receivers shall enter shutdown mode. The frequencies for this signal were selected
with the following constraints:
• Shall be derivable from a standard quartz frequency (e.g., 16 MHz).
• The two tones shall be at least 10 kHz apart from each other (minimum spreading so a
disturbance of both tones from one interference source is unlikely).
• Shall be below 150 kHz for CISPR 11 compliance. It is important to note that the receiver
bandwidth at 150 kHz is 9 kHz and the filter has a roll-off so it is necessary that the chosen
frequencies are below 140 kHz so they do not fall into the detection bandwidth of the EMI-
receiver.
• The arc fault detection shall not be impaired by permanent transmission and the frequencies
below 100 kHz shall be available for arc detection.
The base frequency is 6 250 Hz and the two tones are basically 19 and 21 times the base
frequency as can be seen in Table 6.
7.4 Transmitter
7.4.1 General
The transmitter broadcasts a permission to operate signal using S-FSK modulation. The
transmitter shall have a well-defined output impedance and shall be capable of driving low
impedance loads, see Table 6.
IEC 63257:2026 © IEC 2026
7.4.2 Requirements for the transmitter
7.4.2.1 Transmitter(s) shall continuously send a cyclical code sequence, which includes
‘permission to operate’ when an initiator indicates shutdown is not active, corresponding to the
code sequences defined in Table 6.
7.4.2.2 Transmitter(s) shall have an output impedance in the range specified for Z in the
OUT
transmission frequency band f to f .
M S
7.4.2.3 Transmitter(s) shall provide an open circuit output voltage in the range specified for
.
V
TX
7.4.2.4 Transmitter(s) shall transmit permission to operate signal using a mark and space
tone frequency of f and f respectively.
M S
7.4.2.5 Transmitter(s) shall maintain the transmission of a mark or a space tone for T
S
duration.
7.4.2.6 Transmitter(s) shall transmit ‘permission to operate’ signals according to a fixed duty
cycle defined by an integer number of consecutive transmitted code words followed by an
integer number of zero energy code words.
7.4.2.7 Transmitter(s) shall maintain phase coherency when transitioning between mark and
space tones.
7.4.2.8 Transmitter(s) shall maintain S-FSK tone frequencies (f and f ) and effective bit
M S
rate (RS) to within a ±100 ppm tolerance when in operation inclusive of allowances for
temperature and aging.
7.4.2.9 Transmitter(s) shall ensure that the S-FSK tone frequencies and the effective bit
rate remain proportional to each other for variations within their permitted tolerances.
7.4.3 Transmitter out-of-band emission requirements
The transmitter(s) shall not generate spurious out-of-band signals that could interfere with other
communication systems or with PV system components like MPP tracker or AFPE (see
Annex B).
• The out-of-band spurious frequency components shall not exceed the levels defined in
Table 2 and shown in Figure 6.
Table 2 – Out-of-band spectral mask parameters
Out-of-band spectral mask
f – 4,5 kHz f – 4,5 kHz f + 4,5 kHz f + 4,5 kHz
S S M M
f (kHz) 0  114,25 114,25 135,75 135,75 500
P (dBc) -50 -50 0 0 -50 -50
P Signal level in dBc
IEC 63257:2026 © IEC 2026
Figure 6 – Out-of-band spectrum mask
7.4.4 Transmitter in-band emission requirements
To ensure easy separation of the carriers in the demodulator, the in-band spectrum of the two
FSK carriers shall be limited.
• In-band frequency components shall not exceed the levels defined in Table 3 and shown in
Figure 7.
Table 3 – In-band spectral mask parameters
In-band spectral mask
f − f (kHz) −50 < f ≤ −4,75 −4,75 < f ≤ −0,75 −0,75 < f ≤ 0,75 0,75 < f ≤ 4,75 4,75 < f ≤ 50
c
P (dBc) −50 Linearly rising 0 Linearly falling −50
from −50 dBc to from 0 dBc to
0 dBc −50 dBc
f Carrier-frequency
c
IEC 63257:2026 © IEC 2026
Figure 7 – In-band spectral mask
If the transmitter is integrated into an inverter, then the measurement of the transmitter emission
shall be done when the inverter is in standby. The emission of the inverter during standby or
feed in operation shall not interfere with the power line communication. It is mandatory that the
switching frequency of the inverter (also of the integrated DC/DC converters) and the resulting
spurious emissions do not fall into the communication band of the PLC (see Figure F.12).
7.5 Receiver
7.5.1 General
The receiver(s) shall be able to handle a large range of input signal amplitude. Maximum
amplitude is received with maximum transmit signal level and minimum PV string attenuation,
and conversely, minimum signal is received with minimum transmit signal level and maximum
PV string attenuation.
7.5.2 Requirements for the receiver
7.5.2.1 Receiver(s) shall decode the FSK signals at f and f as sent by the transmitter.
M S
7.5.2.2 Receiver(s) shall indicate the presence of permission to operate signals without
gaps or interruptions over at least a one (1) h observation period in the presence of a compliant
S-FSK signal having a compliant duty cycle and an amplitude in the range I mA –
RXSENSERMS
I mA (see Table 6).
RXMAXRMS
7.5.2.3 Receiver(s) shall meet the requirements of this specification when tested with
compliant signals that are subject to any allowable frequency/timing offset within the tolerances
specified in Table 6.
7.5.2.4 Receiver(s) shall indicate the absence of permission to operate signals in response
to any compliant code other than the designated code sequences, which state a permission to
operate code specified in Table 6.
IEC 63257:2026 © IEC 2026
7.5.2.5 Receiver(s) including their output leads (defined as the cables that connect the SD
to the PV system. Output leads of the SD end at the PV connectors used for the string
connection.) shall have pass-through impedance with absolute values in the range specified for
|Z | and |Z | in Table 6 in the frequency range from 20 kHz up to 200 kHz both in active mode
l u
and in shutdown mode.
For multi-module SD (i.e., SD implementations where modules are connected in series), the
pass-through impedance values shall be multiplied by the maximum quantity of PV modules
intended to be used with such a SD to determine the total impedance.
7.5.2.6 Receiver(s) shall indicate the presence of permission to operate signals without any
false detections in the presence of a standardized noise and interference test signal as specified
in Annex F.
Manufacturers are advised that Keep Alive code word consistency checking should be
implemented. Methods to achieve this include,
...