IEC TS 62257-7-1:2006

TECHNICAL IEC
SPECIFICATION TS 62257-7-1
First edition
2006-12
Recommendations for small renewable energy
and hybrid systems for rural electrification –
Part 7-1:
Generators – Photovoltaic arrays

Reference number
IEC/TS 62257-7-1:2006(E)
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TECHNICAL IEC
SPECIFICATION TS 62257-7-1
First edition
2006-12
Recommendations for small renewable energy
and hybrid systems for rural electrification –
Part 7-1:
Generators – Photovoltaic arrays

© IEC 2006 ⎯ Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
PRICE CODE
XC
Commission Electrotechnique Internationale

International Electrotechnical Commission
For price, see current catalogue
МеждународнаяЭлектротехническаяКомиссия

– 2 – TS 62257-7-1© IEC:2006(E)

CONTENTS
FOREWORD.4

INTRODUCTION.6

1 Scope.7

2 Normative references .8

3 Terms and definitions .9

4 Design.15
4.1 Electrical design.15
4.2 Mechanical design.27
5 Safety issues.28
5.1 General .28
5.2 Protection against electric shock and fire .28
5.3 Protection against overcurrent.28
5.4 Protection against effects of lightning and over-voltage .31
6 Selection and erection of electrical equipment.32
6.1 Component requirements .32
6.2 Location and installation requirements .36
7 Acceptance .43
7.1 General .43
7.2 Conformance with system general specification.43
7.3 Wiring and installation integrity.43
7.4 Open circuit voltage .43
7.5 Open circuit voltage measurements for large PV arrays .44
7.6 Short circuit current measurements .45
7.7 Commissioning records .46
8 Operation/maintenance .47
8.1 General .47
8.2 Safety .47
8.3 Operation and maintenance procedures .47
9 Replacement .47
10 Marking and documentation.48

10.1 Equipment marking.48
10.2 Requirements for signs.48
10.3 Labelling of PV array and PV sub-array junction boxes.48
10.4 Labelling of disconnection devices .48
10.5 Fire emergency information signs.48
10.6 Documentation .49

Annex A (informative) Examples of commissioning records.50
Annex B (informative) Example of maintenance schedule .53
Annex C (informative) Replacement.55
Annex D (informative) Examples of signs.56
Annex E (informative) Case studies .57
Annex F (informative) Double switching in PV array.72

TS 62257-7-1© IEC:2006(E) – 3 –

Figure 1 – General functional configuration of a PV powered system .15

Figure 2a – Unearthed PV array and unearthed d.c. load application circuit.17

Figure 2b – Unearthed PV array and earthed d.c. load application circuit.17

Figure 2c – Unearthed PV array connected to a.c. loads via an isolated PCU

application circuit.18

Figure 2d – Unearthed PV array connected to a.c. loads via a non-isolated PCU

application circuit.18

Figure 2e – Earthed PV array and unearthed d.c. load application circuit.18

Figure 2f – Earthed PV array and earthed d.c. load application circuit.19
Figure 2g – Earthed PV array connected to a.c. loads via an isolated PCU application
circuit.19
Figure 2h – Centre-tapped earthed PV array connected to a.c. loads via an isolated
PCU application circuit.19
Figure 2i – Earthed PV array connected to a.c. loads via a non-isolated PCU
application circuit.19
Figure 2 – PV system earthing configurations .19
Figure 3 – PV array exposed-conductive parts earthing decision tree .20
Figure 4 – Unearthed PV array and d.c. loads configuration.21
Figure 5 – PV array diagram – single string case .22
Figure 6 – PV array diagram – multi-string case.23
Figure 7 – PV array diagram – multi-string case with array divided into sub-arrays .24
Figure 8 – Blocking diode implementation (example) .36
Figure 9 – PV string wiring with minimum loop area .41
Figure D.1 – Example of sign required on PV array junction box (10.3) .56
Figure D.2 – Example of sign required adjacent to PV array main switch (10.4.2.) .56
Figure D.3 – Example of fire emergency information sign required in main building
switchboard (10.5.1) .56
Figure F.1 – Floating PV array operating at maximum power point.73
Figure F.2 – Floating PV array with single earth fault .74
Figure F.3 – Floating PV array with double earth fault.75
Figure F.4 – Floating PV array with double earth fault.76

Table 1 – Voltage domains for PV arrays .7
Table 2 – PV system earthing configurations .16
Table 3 – Number of parallel strings without overcurrent protection, n .29
P
Table 4 – Requirements for location of overcurrent protective devices according to the
earth configuration.30
Table 5 – Current rating of PV array circuits .34
Table 6 – Disconnecting means requirements in PV array installations .37
Table 7 – Location of disconnection devices according to system configuration, where
required .37
Table E.1 – Case studies overview list.57

– 4 – TS 62257-7-1© IEC:2006(E)

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
RECOMMENDATIONS FOR SMALL RENEWABLE ENERGY AND

HYBRID SYSTEMS FOR RURAL ELECTRIFICATION –

Part 7-1: Generators – Photovoltaic arrays

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
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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
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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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 62257-7-1, which is a technical specification, has been prepared by IEC technical
committee 82: Solar photovoltaic energy systems.
This first edition of IEC 62257-7-1 is based on IEC/PAS 62111 (1999); it cancels and replaces
the relevant parts of IEC/PAS 62111.

TS 62257-7-1© IEC:2006(E) – 5 –

The text of this technical specification is based on the following documents:

Enquiry draft Report on voting

82/406A/DTS 82/446/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 of the IEC 62257 series, published under the general title, Recommendations
for small renewable energy and hybrid systems for rural electrification can be found on the
IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual edition of this document may be issued at a later date.

– 6 – TS 62257-7-1© IEC:2006(E)

INTRODUCTION
The IEC 62257 series of publications intends to provide to different players involved in rural

electrification projects (such as project implementers, project contractors, project supervisors,

installers, etc.) documents for the setting-up of renewable energy and hybrid systems with

a.c. voltage below 500 V, d.c. voltage below 750 V and power below 100 kVA.

These publications provide recommendations for

– choosing the right system for the right place;

– designing the system;
– operating and maintaining the system.
These publications are focused only on rural electrification concentrated in, but not specific
to, developing countries. They must not be considered as all-inclusive of rural electrification.
The publications try to promote the use of renewable energies in rural electrification. They do
not deal with clean mechanism developments at this time (CO emission, carbon credit, etc.).
Further developments in this field could be introduced in future steps.
This consistent set of publications is best considered as a whole, with different parts
corresponding to items for the safety and sustainability of systems at the lowest possible life-
cycle cost. One of the main objectives of the series is to provide the minimum sufficient
requirements relevant to the field of application, i.e. for small renewable energy and hybrid
off-grid systems.
The purpose of this part of IEC 62257 is to propose a framework for project development and
management and it includes recommended information that must be taken into consideration
during all the steps of the electrification project.

TS 62257-7-1© IEC:2006(E) – 7 –

RECOMMENDATIONS FOR SMALL RENEWABLE ENERGY AND

HYBRID SYSTEMS FOR RURAL ELECTRIFICATION –

Part 7-1: Generators – Photovoltaic arrays

1 Scope
This part of IEC 62257 specifies the general requirements for erection and operation of PV
arrays in decentralized rural electrification systems.
This technical specification contains requirements for ELV and LV PV arrays (see Table 1).
Particular attention must be paid to voltage level, as this is important for safety reasons and
has an influence on protective measures and on the skill and ability level of people operating
the systems.
Table 1 – Voltage domains for PV arrays
Voltage domain Voltage (volts)
Alternating current Smoothed direct current
ELV
U ≤ 50 V U ≤ 120 V
n oc
LV
50 V < U ≤ 1 000 V 120 V < U ≤ 1 500 V
n oc
Note ELV limits are provided by IEC 61201.

For the sake of completeness, this technical specification gives requirements for d.c. voltages
below and above 120 V. However for rural electrification projects it is strongly recommended
to choose a voltage in the range of extra low voltage, taking into account the assumed skills
of the operators, installers and users. Nevertheless, designers must be aware that decreasing
the voltage means increasing the current and thus transferring voltage hazards to current
risks (risk of fire, etc.).
The following PV array configurations are considered (see Figure 5 to Figure 7):
a) single string of modules;
b) multi-string PV array;
c) PV array divided into several sub-arrays.

Direct current systems, and photovoltaic systems in particular, pose various hazards in
addition to those derived from conventional a.c. power systems, for example the ability to
produce and sustain electrical arcs with currents that are not much greater than normal
operating currents. This technical specification addresses those safety requirements arising
from the particular characteristics of photovoltaic systems.
The aim is to provide safety and fire protection requirements for:
− uninformed persons, including owner(s)/occupier(s) and users of the premises where
photovoltaic arrays are installed;
− informed workers (e.g. electricians) working on these systems; and
− emergency workers (for example fire fighters).
For installation of PV arrays see IEC 60364-7-712.

– 8 – TS 62257-7-1© IEC:2006(E)

2 Normative references
The following referenced documents are indispensable for the application 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 60050-811:1991, International Electrotechnical Vocabulary – Chapter 811: Electric

traction
IEC 60287 (all parts), Electric cables – Calculation of the current rating

IEC 60364 (all parts), Low-voltage electrical installations
IEC 60364-4-41, Low-voltage electrical installations – Part 4-41: Protection for safety –
Protection against electric shock
IEC 60364-5-54, Electrical installations of buildings – Part 5-54: Selection and erection of
electrical equipment – Earthing arrangements, protective conductors and protective bonding
conductors
IEC 60449, Voltage bands for electrical installations of buiildings
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 61140, Protection against electric shock – Common aspects for installation and
equipment
IEC 61173, Over-voltage protection for photovoltaic (PV) power generating systems – Guide
IEC 61201, Extra-low voltage (ELV) – Limit values
IEC 61215, Crystalline silicon terrestrial photovoltaic (PV) modules − Design qualification and
type approval
IEC 61643-12, Low voltage surge protective devices − Part 12: Surge protective devices
connected to low voltage power distribution systems − Selection and application principles
IEC 61646, Thin−film terrestrial photovoltaic (PV) modules − Design qualification and type
approval
IEC 62257-5, Recommendations for small renewable energy and hybrid systems for rural
electrification – Part 5: Protection against electrical hazards
IEC 62257-6, Recommendations for small renewable energy and hybrid systems for rural
electrification – Part 6: Acceptance, operation, maintenance and replacement
IEC 62305-2, Protection against lightning – Part 2: Risk management
IEC 62305-3, Protection against lightning – Part 3: Physical damage to structures and life
hazard
TS 62257-7-1© IEC:2006(E) – 9 –

3 Terms and definitions
3.1
available, readily
capable of being reached for inspection, maintenance or repairs without necessitating the

dismantling of structural parts, cupboards, benches or the like

3.2
blocking diode
diode connected in series to module(s), panel(s), sub-arrays and array(s) to block reverse

current into such module(s), panel(s), sub-array(s) and array(s)

3.3
bypass diode
diode connected across one or more cells in the forward current direction to allow the module
current to bypass shaded or broken cells to prevent hot spot or hot cell damage resulting from
the reverse voltage biasing from the other cells in that module
3.4
cable
assembly of one or more conductors and/or optical fibres, with a protective covering and
possibly filling, insulating and protective material
[IEV 151-12-38]
3.5
cable core
the conductor with its insulation but not including any mechanical protective covering
3.6
shield (of a cable)
a surrounding earthed metallic layer to confine the electric field within the cable and/or to
protect the cable from external electrical influence
Note Metallic sheaths, armour and earthed concentric conductors may also serve as shields.
[IEV 461-03-04]
3.7
class I equipment
equipment in which protection against electric shock does not rely on basic insulation only,
but which includes an additional safety precaution in that accessible conductive parts are
connected to the protective earthing conductor in the fixed wiring of the electrical installation

in such a way that accessible parts cannot become live in the event of a failure of the basic
insulation
NOTE 1 Class I equipment may have parts with double insulation or parts operating at SELV.
NOTE 2 For equipment intended for use with a flexible cord or cable, this provision includes a protective earthing
conductor as part of the flexible cord or cable.
3.8
class II equipment
equipment in which protection against electric shock does not rely on basic insulation only,
but in which additional safety precautions such as double insulation or reinforced insulation
are provided, there being no provision for protective earthing or reliance upon installation
conditions. Such equipment may be one of the following types:
− equipment having durable and substantially continuous enclosures of insulating material
which envelops all metal parts, with the exception of small parts, such as nameplates,
screws and rivets, which are isolated from live parts by insulation at least equivalent to
reinforced insulation. Such equipment is called insulation-encased Class II equipment;

– 10 – TS 62257-7-1© IEC:2006(E)

− equipment having a substantially continuous metal enclosure, in which double insulation is

used throughout, except for those parts where reinforced insulation is used, because the

application of double insulation is manifestly impracticable. Such equipment is called

metal-encased Class II equipment;

− equipment that is a combination of the types described in Items (a) and (b)

NOTE 1 The enclosure of insulation-encased Class II equipment may form part of the whole of the supplementary

insulation or of the reinforced insulation.

NOTE 2 If the equipment with double insulation or reinforced insulation throughout has an earthing terminal or

earthing contact, it is considered to be of Class I construction.

NOTE 3 Class II equipment may be provided with means for maintaining the continuity of protective circuits,
insulated from accessible conductive parts by double insulation or reinforced insulation.
NOTE 4 Class II equipment may have parts operating at SELV.
3.9
class III equipment
equipment in which protection against electric shock relies on supply at SELV and in which
voltages higher than those of SELV are not generated
NOTE Equipment intended to be operated at SELV and which have internal circuits that operate at a voltage other
than SELV are not included in the classification and are subject to additional requirements.
3.10
double insulation
insulation comprising both basic insulation and supplementary insulation
[IEV 195-06-08]
3.11
earthing
a protection against electric shocks
3.12
extra-low voltage
ELV
voltage not exceeding the relevant voltage limit of band I specified in IEC 60449
[IEV 826-12-30]
NOTE 1 See also IEC 61201.
NOTE 2 Voltage not exceeding 50 V a.c. and 120 V d.c. ripple free are considered to be ELV.
3.13
I
MOD_REVERSE
the current a module can withstand in the reverse direction to normal without damage to the
module. This rating is obtained from the manufacturer at expected operating conditions
NOTE 1 This current rating does not relate to bypass diode rating. The module reverse current is the current
flowing through the PV cells in the reverse direction to normal current.
NOTE 2 A typical figure for crystalline silicon modules is between 2 and 2,6 times the normal short circuit current
rating ISC MOD.
3.14
I
SC MOD
the short circuit current of a PV module or PV string at Standard Test Conditions (STC), as
specified by the manufacturer in the product specification plate
NOTE As PV strings are a group of PV modules connected in series, the short circuit current of a string is equal
to I .
SC MOD
TS 62257-7-1© IEC:2006(E) – 11 –

3.15
I
SC S-ARRAY
the short circuit current of a PV sub-array at Standard Test Conditions (STC), and equal to:

I = I × S
SC S-ARRAY SC STC MOD SA
where S is the number of parallel-connected PV strings in the PV sub-array

SA
3.16
I
SC ARRAY
the short circuit current of the PV array at Standard Test Conditions, and is equal to:

I = I × S
SC ARRAY SC STC MOD A
where S is the total number of parallel-connected PV strings in the PV array
A
3.17
junction box
closed or protected connecting device allowing making of one or several junctions
[IEV 442-08-03]
3.18
live part
conductor or conductive part intended to be energized in normal operation, including a neutral
conductor, but by convention not a PEN conductor or PEM conductor or PEL conductor
NOTE This concept does not necessarily imply a risk of electric shock.
[IEV 195-02-19]
3.19
PEL conductor
conductor combining the functions of both a protective earthing conductor and a line
conductor
[IEV 195-02-14]
3.20
protected extra-low voltage
PELV
an extra-low voltage system which is not electrically separated from earth, but which
otherwise satisfies all the requirements for SELV

3.21
PEM conductor
conductor combining the functions of both a protective earthing conductor and a midpoint
conductor
[IEV 195-02-13]
3.22
PEN conductor
conductor combining the functions of both a protective earthing conductor and a neutral
conductor
[IEV 195-02-12]
– 12 – TS 62257-7-1© IEC:2006(E)

3.23
power conditioning unit
PCU
a system that converts the electrical power delivered by the PV array into the appropriate

frequency and/or voltage values to be delivered to the load, or stored in a battery or injected

into the electricity grid (see Figure 5 to Figure 7)

3.24
power conditioning unit, isolated

a power conditioning unit where there is electrical separation between the input and output
circuits (e.g. by means of an isolation transformer)

3.25
power conditioning unit, non-isolated
a power conditioning unit where there is no electrical separation between the input and output
circuits
3.26
PV array
a) a mechanically integrated assembly of modules or panels and support structure that forms
a d.c. electricity-producing unit. An array does not include foundation, tracking apparatus,
thermal control, and other such components
1)
, definition 3.3.45 a) ]
[IEC 61836, Ed.2
b) a mechanically and electrically integrated assembly of PV modules, and other necessary
components, to form a DC power supply unit
[IEC 60364-7-712, definition 712.3.4]
NOTE A PV array may consist of a single PV module, a single PV string, or several parallel-connected strings, or
several parallel-connected PV sub-arrays and their associated electrical components (see Figure 5 to Figure 7).
For the purposes of this standard the boundary of a PV array is the output side of the PV array disconnecting
device. Two or more PV arrays, which are not interconnected in parallel on the generation side of the power
conditioning unit, shall be considered as independent PV arrays.
3.27
PV array cable
the output cable of a PV array that connects the PV array junction box to the PV array
disconnecting device
3.28
PV array, earthed
a PV array where one of the poles of the d.c. output circuit is electrically bonded to earth

3.29
PV array, floating
a PV array where none of the poles of the d.c. output circuit is electrically bonded to earth
3.30
PV array, isolated
a PV array where there is at least a simple electrical separation between the PV array output
circuit (d.c. side) and the a.c. system
NOTE A simple electrical separation of power circuits is usually achieved by means of a power transformer.
3.31
PV array junction box
a junction box where all strings of any array are connected
___________
1)
In preparation.
TS 62257-7-1© IEC:2006(E) – 13 –

[IEC 60364-7-712, definition 712.3.5, modified]

3.32
PV array voltage
the PV array voltage is considered to be equal to V under worst case conditions
OC ARRAY
NOTE The open circuit voltage is dependent on the cell temperature and technology.

3.33
PV cell
a) the basic unit of photovoltaic conversion, a semiconductor device that can convert light

directly into electrical energy;

b) the basic photovoltaic device [see IEC 60904-3]
NOTE The preferred term is "solar photovoltaic cell" or "photovoltaic cell", colloquially referred to as a "solar cell".
3.34
PV module
the smallest complete environmentally protected assembly of interconnected cells
[see IEC 60904-3, IEC 61277]
NOTE Colloquially referred to as a "solar module".
3.35
PV module junction box
an enclosure affixed to a PV module, where the electrical connections to the PV module are
made
3.36
PV string
a circuit of series-connected modules
3.37
PV string cable
a cable connecting the modules in a PV string, or connecting the string to a junction box or to
the d.c. terminals of the power conditioning unit (see Figure 5 to Figure 7)
3.38
PV sub-array
the portion of an array that can be considered as a unit
[IEC 61277, definition B.12, modified]

3.39
PV sub-array cable
the output cable of a PV sub-array that carries only the output current of its associated sub-
array in normal operation, and that connects the PV sub-array with the other PV sub-arrays
that constitute the PV array
NOTE PV sub-array cables are only relevant for PV arrays that are divided into sub-arrays (see Figure 7 for
clarification).
3.40
PV sub-array junction box
an enclosure where all the PV strings of a PV sub-array are electrically connected in parallel
and where protection devices may be located if necessary (see Figure 7)
NOTE PV sub-array junction boxes are only relevant for PV arrays that are divided into sub-arrays

– 14 – TS 62257-7-1© IEC:2006(E)

3.41
reinforced insulation
insulation of hazardous-live-parts which provides a degree of protection against electric shock

equivalent to double insulation

NOTE Reinforced insulation may comprise several layers which cannot be tested singly as basic insulation or

supplementary insulation.
[IEV 195-06-09]
3.42
supplementary insulation
independent insulation applied in addition to basic insulation, for fault protection

[IEV 195-06-07]
3.43
simple separation
separation between electric circuits or between an electric on a local earth by means of basic
insulation
[IEV 826-12-28]
3.44
ripple-free d.c.
for sinusoidal ripple voltage, a ripple content not exceeding 10% r.m.s.
NOTE Therefore the maximum peak value does not exceed 120 V for a nominal 108 V ripple-free d.c. system.
3.45
SELV
safety extra-low voltage
an extra-low voltage system which is electrically separated from earth and from other systems
in such a way that a single fault cannot give rise to the risk of electric shock
3.46
STC
Standard Test Conditions
a standard set of reference conditions used for the testing and rating of photovoltaic cells and
modules. The Standard test conditions are:
a) PV cell temperature of 25 ºC;
b) irradiance in the plane of the PV cell or module of 1000 W/m ;
c) light spectrum corresponding to an atmospheric air mass of 1,5

3.47
V
OC MOD
the open circuit voltage of a PV module at Standard Test Conditions, as specified by the
manufacturer in the product specification
3.48
V
OC ARRAY
the open circuit voltage at Standard Test Conditions of a PV array, and is equal to:
V = V × M
OC ARRAY OC MOD
where M is the number of series-connected PV modules in any PV string of the PV array.
NOTE This standard assumes that all strings within a PV array are connected in parallel; hence the open circuit
voltage of PV sub-arrays and PV strings is equal to V .
OC ARRAY
TS 62257-7-1© IEC:2006(E) – 15 –

3.49
voltage
differences of potential normally existing between conductors and between conductors and

earth as follows:
a) extra-low voltage: not exceeding 50 V a.c. or 120 V ripple-free d.c.;

b) low voltage: exceeding extra-low voltage, but not exceeding 1 000 V a.c. or 1 500 V d.c.

c) high voltage: exceeding low voltage.

NOTE In consideration of ELV status, V must be used.
OC ARRAY
4 Design
4.1 Electrical design
4.1.1 Functional configuration of PV powered systems
Figure 1 illustrates the general functional configuration of a PV powered system.
Application
PV
circuit
array
Array
circuit
IEC  2338/06
Figure 1 – General functional configuration of a PV powered system
Three kinds of application circuit are considered:
– PV array is connected to DC loads;
– PV array is connected to AC loads via conversion equipment;

– PV array is connected to AC grid forming elements via conversion equipment.
Except where the array is less than 200 W and the array voltage is ELV, all current-carrying
conductors from the array shall be capable of being interrupted using a load-breaking switch.
NOTE In unearthed systems this is a general requirement of IEC 60364.
In earthed systems (where the application circuit is earthed), the switch is required to interrupt
current caused by an earth fault within the array.
Because the array is current limited, overcurrent protection cannot provide interruption of this
fault situation.
– 16 – TS 62257-7-1© IEC:2006(E)

4.1.2 PV array earthing
4.1.2.1 General
To consider the PV array earthing it is necessary to consider the complete PV system
earthing configuration. Two separate issues are addressed:

− earthing of the main current carrying conductors of the array (system earthing);

− earthing of exposed conductive parts for lightning protection and/or equipotential
bonding.
NOTE To realize earthing on the field, see IEC 62305-3.

4.1.2.2 PV array system earthing
In the following Table 2, several configurations are considered. No consideration is given to
earthing of exposed conductive parts, which is covered in the following clause.
Table 2 – PV system earthing configurations
Photovoltaic array Figures Application circuit Consequence on the status of the PV
earthing array
equipment
Figure 2a Unearthed DC loads Floating
Unearthed Figure 2b Earthed DC loads
Fixed to earth
Figure 2c AC loads connected via isolated Floating
PCU
Figure 2d AC loads connected via a non- Fixed by the status of the neutral of the
isolated power conditioning unit application circuit
Figure 2e Unearthed DC loads
a b
Earthed  Fixed to earth
Figure 2f Earthed DC loads
Figure 2g,2h AC loads connected via isolated
PCU
Figure 2i AC loads connected via a non- Not permitted according to IEC 60364
isolated power conditioning unit
PCU
a
In non-centre-tapped, earthed PV arrays, either the positive or negative pole could be connected to the earth,
but the preferred configuration is to earth the negative, because connecting the positive to earth could result in
corrosion of the earthing electrode.
b
In a centre-tapped earthed PV array where the PV array is equally divided into two segments connected in series
and the midpoint connected to earth. The “consequences on the status of the PV array” column is not changed
whether the array is centre-tapped earthed or earthed on only one pole.

The requirements of manufacturers of power conditioning equipment to which the PV array is
connected shall be taken into account in determining the most appropriate system earthing
arrangement.
The following subfigures of Figure 2 illustrate the system earthing arrangements listed in
Table 2:
TS 62257-7-1© IEC:2006(E) – 17 –

DC
PV
loads
array
Array Application
circuit circuit
IEC  2339/06
Figure 2a – Unearthed PV array and unearthed d.c. load application circuit

DC
PV
loads
array
Application
circuit
Array
circuit
IEC  2340/06
Figure 2b – Unearthed PV array and earthed d.c. load application circuit

– 18 – TS 62257-7-1© IEC:2006(E)

Phase
PV
N
array
Isolated PCU
Application
Array
circuit circuit
IEC  2341/06
Figure 2c – Unearthed PV array connected to a.c. loads via an isolated PCU application circuit

Phase
PV
N
array
Non-isolated PCU
Array
Application
circuit
circuit
IEC  2342/06
Figure 2d – Unearthed PV array connected to a.c. loads via a non-isolated PCU application circuit

DC
PV
loads
array
Application
Array
circuit
circuit
IEC  2343/06
Figure 2e – Earthed PV array and unearthed d.c. load application circuit

TS 62257-7-1© IEC:2006(E) – 19 –

DC
PV
loads
array
Application
Array circuit
circuit
IEC  2344/06
Figure 2f – Earthed PV array and earthed d.c. load application circuit
Phase
PV
N
array
Isolated PCU
Array Application
circuit circuit
IEC  2345/06
Figure 2g – Earthed PV array connected to a.c. loads via an isolated
PCU application circuit
Phase
PV
N
array
Isolated PCU
Array Application
circuit circuit
IEC  2346/06
Figure 2h – Centre-tapped earthed PV array connected to a.c. loads
via an isolated PCU application circuit
Phase
PV
N
array
Non-isolated PCU
Array Application
circuit circuit
IEC  2347/06
NOTE This configuration is not permitted.
Figure 2i – Earthed PV array connected to a.c. loads
via a non-isolated PCU application circuit
Figure 2 – PV system earthing configurations

– 20 – TS 62257-7-1© IEC:2006(E)

4.1.2.3 Earthing of exposed conductive parts and equipotential bonding

There are three possible reasons for earthing exposed conductive parts of a PV array:

a) protective earthing to provide a path for fault currents to flow;

b) lightning protection;
c) equipotential bonding to avoid uneven potentials across an installation.

An earth conductor may perform one or more of these functions in an installation.
...