ASTM E2908-12(2023)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E2908 − 12 (Reapproved 2023) An American National Standard
Standard Guide for
Fire Prevention for Photovoltaic Panels, Modules, and
Systems
This standard is issued under the fixed designation E2908; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This guide describes basic principles of photovoltaic
module design, panel assembly, and system installation to
2. Referenced Documents
reduce the risk of fire originating from the photovoltaic source
2.1 ASTM Standards:
circuit.
E772 Terminology of Solar Energy Conversion
1.2 This guide is not intended to cover all scenarios which
E2481 Test Method for Hot Spot Protection Testing of
could lead to fire. It is intended to provide an assembly of
Photovoltaic Modules
generally accepted practices.
2.2 Other Standards and Documents:
1.3 This guide is intended for systems which contain pho-
IEC 61215 Crystalline silicon terrestrial photovoltaic (PV)
tovoltaic modules and panels as dc source circuits, although the
modules—Design qualification and type approval
recommended practices may also apply to systems utilizing ac
IEC 61730 Photovoltaic (PV) module safety qualification
modules.
North American Board of Certified Energy Practitioners
(NABCEP) Study Guide for Photovoltaic System Install-
1.4 This guide does not cover fire suppression in the event
ers
of a fire involving a photovoltaic module or system.
NFPA 70 U.S. National Electrical Code (article 690)
1.5 This guide does not cover fire emanating from other
UL 1703 Standard for Flat-Plate Photovoltaic Modules and
sources.
Panels
1.6 This guide does not cover mechanical, structural,
UL 1741 Inverters, Converters, and Controllers for Use in
electrical, or other considerations key to photovoltaic module
Independent Power Systems
and system design and installation.
3. Terminology
1.7 This guide does not cover disposal of modules damaged
3.1 Definitions of terms used in this standard may be found
by a fire, or other material hazards related to such modules.
in Terminology E772.
1.8 Units—The values stated in SI units are to be regarded
3.2 Definitions:
as standard. No other units of measurement are included in this
3.2.1 ground fault, n—a condition where there is an unin-
standard.
tended electrical connection between the active PV circuit and
1.9 This standard does not purport to address all of the
ground.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
4. Summary of Practice
priate safety, health, and environmental practices and deter-
4.1 Photovoltaic modules and panels should be designed to
mine the applicability of regulatory limitations prior to use.
minimize the risk of fire and should be assembled with good
1.10 This international standard was developed in accor-
quality control practices.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the 4.2 Photovoltaic systems should be designed to minimize
Development of International Standards, Guides and Recom-
the risk of fire, and installed with fire safety in mind. Installers
should be aware of PV-related fires that have occurred and the
cause of those fires.
This guide is under the jurisdiction of ASTM Committee E44 on Solar,
Geothermal and Other Alternative Energy Sources and is the direct responsibility of
Subcommittee E44.09 on Photovoltaic Electric Power Conversion. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Aug. 1, 2023. Published August 2023. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2012. Last previous edition approved in 2018 as E2908 – 12 (2018). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/E2908-12R23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2908 − 12 (2023)
5. Significance and Use 7. PV Modules and Panels
5.1 Photovoltaic modules are electrical dc sources. dc
7.1 Design Against Arcing—Modules shall be designed to
sources have unique considerations with regards to arc forma-
reduce the risk of arcing.
tion and interruption, as once formed, the arc is not automati-
7.1.1 Modules shall meet the spacing requirements of IEC
cally interrupted by an alternating current. Solar modules are
61730 or UL 1703 to reduce the occurrence of arcing under
energized whenever modules in the string are illuminated by
both normal operating conditions and fault conditions.
sunlight, or during fault conditions.
7.1.2 Materials and processes used in the manufacture of PV
5.2 With the rapid increase in the number of photovoltaic modules shall be designed to be durable and reliable over the
system installations, this guide attempts to increase awareness entire service life of the PV module.
of methods to reduce the risk of fire from photovoltaic systems.
7.1.3 Failure mechanisms, such as mismatch of thermal
expansion coefficients, metal fatigue, corrosion or vibration,
5.3 This guide is intended for use by module manufacturers,
shall be considered during the selection of materials, module
panel assemblers, system designers, installers, and specifiers.
layout, and assembly.
5.4 This guide may be used to specify minimum require-
7.1.4 Material selection shall include consideration of the
ments. It is not intended to capture all conditions or scenarios
operating temperatures of the material and aging characteristics
which could result in a fire.
of the material.
6. Arcing
7.2 Design for Arc and Fire Suppression:
6.1 dc Arcing:
7.2.1 Materials in close contact to potential arc sources,
6.1.1 An electrical arc can form where an electric potential
such as junction boxes, shall have a minimum arc and
exists between two neighboring conductors. Unlike ac arcs
flammability rating in accordance with IEC 61730 or UL 1703.
which may be extinguished during the alternating cycle of
This helps to reduce the risk of fire in the event of an arcing
current, a dc arc will be maintained indefinitely until inter-
event.
rupted. A dc arc will be sustained until the voltage potential is
7.2.2 According to the 2011 National Electrical Code, an arc
reduced, an arc-detection device disrupts the flow of current, or
detection device is required to disconnect the current flow in
the effective distance between the conductors becomes too
the event of arcing. Depending on the location of the device, it
large to sustain the arc. Even once the arc is eliminated, the arc
may protect an individual module or an entire string. Consid-
may have been sufficient to cause burning or ignition of
eration shall be given to the reliability of such devices, to avoid
surrounding materials.
nuisance trips and costly servicing.
6.1.2 An arc may propagate across the surface of the module
7.3 Operating Temperature:
(for example, along the gap between rows of cells) as materials
7.3.1 A PV module converts a portion of the sun’s energy
are burned away.
into electrical energy. The portion of the sun’s energy that is
6.1.3 The arc may extinguish and re-ignite under variable
not converted into electrical energy is either reflected, trans-
environmental conditions or with expansion and contraction of
mitted through the module, or transformed into heat energy.
affected materials, and may also extinguish at night and restart
Therefore, a PV module usually operates at a temperature
the next day.
hotter than the surrounding ambient temperature.
6.1.4 Common sources of arcs in PV modules:
7.3.2 Operating Temperature Considerations—The exact
6.1.4.1 Cracks in solar cells (crystalline or thin film).
operating temperature of a module, and of any given compo-
6.1.4.2 Inadequate spacing between parts of different volt-
nent within a module, depends on a variety of factors.
age potentials.
6.1.4.3 Improper bonding of interconnects to cells. 7.3.2.1 Environmental Factors—Wind speed, wind
6.1.4.4 Improper bonding of interconnects to bus bar. direction, ambient temperature, solar irradiance, and cloud
cover.
6.1.4.5 Improper bonding of bus bar to wiring terminal or
connector.
7.3.2.2 Installation Factors—Angle of installation, rack
6.1.4.6 Insufficient allowance for thermal expansion and
type, module spacing, location, wind obstructions, tracking
contraction of materials, which leads to mechanical fatigue.
versus non-tracking, ventilation, shading events.
Common examples include cell interconnects and expansion
7.3.2.3 Module Factors—Cell mismatch (leading to nonuni-
joints in conduits.
form heat generation), insulated sections (e.g. junction boxes),
6.1.4.7 Insufficient strain relief between parts, especially
color, framing, transparency, material thermal conductivity,
field wiring terminations, solder joints, and internal conduc-
thermal convection characteristics, current-carrying limits of
tors.
live parts.
6.2 ac Arcing: 7.3.3 Shading—Shading events can cause shaded cells to act
6.2.1 Both ac and dc circuits may be present in a solar as power sinks (resistors) as opposed to power generators.
photovoltaic system, and both circuits contain potential arc Therefore, shaded cells can run much hotter than neighboring
sources. A dc arc may be sustained over a larger distance and cells. Although modules are designed to operate in unshaded
longer duration than an ac arc due to the one-directional flow conditions, some degree of localized shading is inevitable in
of the dc current, which is not easily interrupted. The current in most installations. Refer to Test Method E2481 for additional
an ac arc always goes to zero twice per cycle. information.
E2908 − 12 (2023)
7.3.3.1 The amount of heating of a cell depends on the shunt the extreme and nominal conditions expected throughout the
and series resistance characteristics of the shaded cells, the module lifetime. The means for connection shall be in accor-
current flowing through the cell, and whether the cells are dance with the module and connector installation guides or any
partially illuminated. applicable local codes. Wiring shall be mechanically secured, if
7.3.3.2 Material Combustion—Materials in contact with required, to prevent strain on the electrical connections, with
cells shall be able to withstand temperatures under the shaded adequate slack to allow for thermal expansion and contraction
condition without exceeding material ignition temperature of the wiring.
ratings. The design may be tested to assess material suitability
8.1.3 Other Wiring—All other wiring in the PV system shall
per UL 1703, Section 19, Temperature Test.
be suitable for the intended application and secured if required,
7.3.3.3 Modules shall have adequate protection in the event
with consideration given to the same factors as described for
of shading.
module-to-module wiring. Wiring securement means must be
7.3.3.4 Diodes—A common method for providing shading
able to withstand outdoor conditions, including UV radiation,
protection is through bypass diodes connecte
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