ASTM E2908-12
(Guide)Standard Guide for Fire Prevention for Photovoltaic Panels, Modules, and Systems
Standard Guide for Fire Prevention for Photovoltaic Panels, Modules, and Systems
SIGNIFICANCE AND USE
5.1 Photovoltaic modules are electrical dc sources. dc sources have unique considerations with regards to arc formation and interruption, as once formed, the arc is not automatically interrupted by an alternating current. Solar modules are energized whenever modules in the string are illuminated by sunlight, or during fault conditions.
5.2 With the rapid increase in the number of photovoltaic system installations, this guide attempts to increase awareness of methods to reduce the risk of fire from photovoltaic systems.
5.3 This guide is intended for use by module manufacturers, panel assemblers, system designers, installers, and specifiers.
5.4 This guide may be used to specify minimum requirements. It is not intended to capture all conditions or scenarios which could result in a fire.
SCOPE
1.1 This guide describes basic principles of photovoltaic module design, panel assembly, and system installation to reduce the risk of fire originating from the photovoltaic source circuit.
1.2 This guide is not intended to cover all scenarios which could lead to fire. It is intended to provide an assembly of generally-accepted practices.
1.3 This guide is intended for systems which contain photovoltaic modules and panels as dc source circuits, although the recommended practices may also apply to systems utilizing ac modules.
1.4 This guide does not cover fire suppression in the event of a fire involving a photovoltaic module or system.
1.5 This guide does not cover fire emanating from other sources.
1.6 This guide does not cover mechanical, structural, electrical, or other considerations key to photovoltaic module and system design and installation.
1.7 This guide does not cover disposal of modules damaged by a fire, or other material hazards related to such modules.
1.8 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E2908 − 12
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 2. Referenced Documents
1.1 This guide describes basic principles of photovoltaic 2.1 ASTM Standards:
module design, panel assembly, and system installation to E772 Terminology of Solar Energy Conversion
reduce the risk of fire originating from the photovoltaic source E2481 Test Method for Hot Spot Protection Testing of
circuit. Photovoltaic Modules
1.2 This guide is not intended to cover all scenarios which 2.2 Other Standards and Documents:
could lead to fire. It is intended to provide an assembly of IEC 61215 Crystalline silicon terrestrial photovoltaic (PV)
generally-accepted practices. modules—Design qualification and type approval
IEC 61730 Photovoltaic (PV) module safety qualification
1.3 This guide is intended for systems which contain pho-
North American Board of Certified Energy Practitioners
tovoltaicmodulesandpanelsasdcsourcecircuits,althoughthe
(NABCEP), Study Guide for Photovoltaic System Install-
recommended practices may also apply to systems utilizing ac
ers
modules.
NFPA 70 US National Electrical Code (article 690)
1.4 This guide does not cover fire suppression in the event
UL 1703 Standard for Flat-Plate Photovoltaic Modules and
of a fire involving a photovoltaic module or system.
Panels
UL 1741 Inverters, Converters, and Controllers for Use in
1.5 This guide does not cover fire emanating from other
Independent Power Systems
sources.
1.6 This guide does not cover mechanical, structural,
3. Terminology
electrical, or other considerations key to photovoltaic module
and system design and installation. 3.1 Definitions of terms used in this standard may be found
in Terminology E772.
1.7 This guide does not cover disposal of modules damaged
by a fire, or other material hazards related to such modules. 3.2 Definitions:
3.2.1 ground fault, n—a condition where there is an unin-
1.8 Units—The values stated in SI units are to be regarded
tended electrical connection between the active PV circuit and
as standard. No other units of measurement are included in this
ground.
standard.
1.9 This standard does not purport to address all of the
4. Summary of Practice
safety concerns, if any, associated with its use. It is the
4.1 Photovoltaic modules and panels should be designed to
responsibility of the user of this standard to establish appro-
minimize the risk of fire and should be assembled with good
priate safety and health practices and determine the applica-
quality-control practices.
bility of regulatory limitations prior to use.
This test method is under the jurisdiction of ASTM Committee E44 on Solar,
Geothermal and OtherAlternative Energy Sources and is the direct responsibility of For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Subcommittee E44.09 on Photovoltaic Electric Power Conversion. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Dec. 1, 2012. Published December 2012. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E2908-12. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2908 − 12
4.2 Photovoltaic systems should be designed to minimize 6.2.1 Both ac and dc circuits may be present in a solar
the risk of fire, and installed with fire safety in mind. Installers photovoltaic system, and both circuits contain potential arc
should be aware of PV-related fires that have occurred and the sources. A dc arc may be sustained over a larger distance and
cause of those fires. longer duration than an ac arc due to the one-directional flow
ofthedccurrent,whichisnoteasilyinterrupted.Thecurrentin
5. Significance and Use an ac arc always goes to zero twice per cycle.
5.1 Photovoltaic modules are electrical dc sources. dc
7. PV Modules and Panels
sources have unique considerations with regards to arc forma-
7.1 Design Against Arcing—Modules shall be designed to
tion and interruption, as once formed, the arc is not automati-
reduce the risk of arcing.
cally interrupted by an alternating current. Solar modules are
7.1.1 Modules shall meet the spacing requirements of IEC
energized whenever modules in the string are illuminated by
61730 or UL 1703 to reduce the occurrence of arcing under
sunlight, or during fault conditions.
both normal operating conditions and fault conditions.
5.2 With the rapid increase in the number of photovoltaic
7.1.2 MaterialsandprocessesusedinthemanufactureofPV
system installations, this guide attempts to increase awareness
modules shall be designed to be durable and reliable over the
ofmethodstoreducetheriskoffirefromphotovoltaicsystems.
entire service life of the PV module.
5.3 This guide is intended for use by module manufacturers, 7.1.3 Failure mechanisms, such as mismatch of thermal
expansion coefficients, metal fatigue, corrosion or vibration,
panel assemblers, system designers, installers, and specifiers.
shall be considered during the selection of materials, module
5.4 This guide may be used to specify minimum require-
lay-out, and assembly.
ments. It is not intended to capture all conditions or scenarios
7.1.4 Material selection shall include consideration of the
which could result in a fire.
operatingtemperaturesofthematerialandagingcharacteristics
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 UL1703.
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
reduced,anarc-detectiondevicedisruptstheflowofcurrent,or
arc-detection device is required to disconnect the current flow
the effective distance between the conductors becomes too
in the event of arcing. Depending on the location of the device,
large to sustain the arc. Even once the arc is eliminated, the arc
it may protect an individual module or an entire string.
may have been sufficient to cause burning or ignition of
Consideration shall be given to the reliability of such devices,
surrounding materials.
to avoid nuisance trips and costly servicing.
6.1.2 Anarcmaypropagateacrossthesurfaceofthemodule
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.
7.3.2.1 Environmental Factors—Wind speed, wind
6.1.4.3 Improper bonding of interconnects to cells.
direction, ambient temperature, solar irradiance, and cloud
6.1.4.4 Improper bonding of interconnects to bus bar.
cover.
6.1.4.5 Improper bonding of bus bar to wiring terminal or
7.3.2.2 Installation Factors—Angle of installation, rack
connector.
type, module spacing, location, wind obstructions, tracking
6.1.4.6 Insufficient allowance for thermal expansion and
versus non-tracking, ventilation, shading events.
contraction of materials, which leads to mechanical fatigue.
7.3.2.3 Module Factors—Cell mismatch (leading to non-
Common examples include cell interconnects and expansion
uniform heat generation), insulated sections (e.g. junction
joints in conduits.
boxes), color, framing, transparency, material thermal
6.1.4.7 Insufficient strain relief between parts; especially
conductivity, thermal convection characteristics, current-
field wiring terminations, solder joints, and internal conduc-
carrying limits of live parts.
tors.
7.3.3 Shading—Shadingeventscancauseshadedcellstoact
6.2 ac Arcing: as power sinks (resistors) as opposed to power generators.
E2908 − 12
Therefore, shaded cells can run much hotter than neighboring 8.1.2 Module-to-Module Connections—All wiring and con-
cells. Although modules are designed to operate in un-shaded nectors used shall be of the type and sizing recommended by
conditions, some degree of localized shading is inevitable in the module manufacturer and in accordance with local codes.
most installations. Refer to Test Method E2481 for additional Wiring shall be suitable for the intended application, including
information. temperature range, wire gauge, UV resistance, water
resistance, and system voltage. Consideration shall be given to
7.3.3.1 Theamountofheatingofacelldependsontheshunt
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
partially illuminated.
any applicable local codes. Wiring shall be mechanically
7.3.3.2 Material Combustion—Materials in contact with
secured, if required, to prevent strain on the electrical
cells shall be able to withstand temperatures under the shaded
connections, with adequate slack to allow for thermal expan-
condition without exceeding material ignition temperature
sion and contraction of the wiring.
ratings. The design may be tested to assess material suitability
8.1.3 Other Wiring—All other wiring in the PVsystem 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 connected in parallel with
over the expected service life of the system, and should be
the cells to be protected. As the forward and reverse charac-
checked routinely as part of regular system maintenance. If
teristics of a PV cell are different, the diodes shall be sized to
wiring is in metallic conduit, particular attention should be
activate in the event of shading of part or all of one or more of
giventoproperinstallationandwiremanagementtechniquesto
the cells to prevent the formation of localized hot spots. The
reduce the possibility of ground faults.
diodes must be able to safely handle the string current.
8.1.4 dc Disconnects—dc disconnects shall be used to allow
Activation of the diode during a cell shading event shall not
safe disconnection of a dc string from an inverter, combiner
result in overheating of the diode, nor materials surrounding
box, charge controller or other electrical components in the
the diode. The diode shall be mounted and connected using a
system. The disconnect shall be rated appropriately for the dc
robust and reliable method, including strain relief as appropri-
current and voltage of the system, in accordance with local
ate. Diode quality and the mounting method should be evalu-
codes. Note that an ac-only disconnect may or may not be
ated for durability. If diodes are mounted mechanically, they
suitable for a dc circuit, as it relies on the alternating-nature of
should be tested under simulated field conditions to ensure that
ac current to disrupt the current flow.
adequate contact is maintained over time.
8.1.5 Inverters—Inverters shall be appropriately sized for
7.4 Documentation:
the intended location, be approved to the local standard, such
7.4.1 Recognition—The module should be certified by an
as UL 1741, and meet local code requirements for connection
approved organization to meet a minimum level of safety. Two
tothegrid.Invertersmayhavebuilt-inarc-detectioncapability,
standards that are commonly used to assess a minimum safety
which disconnects the system in the event of an arc to reduce
level are UL 1703 and IEC 61730.
damage to the system and supporting structures.
7.4.2 Quality System—The PV manufacturer shall have an
8.1.6 Ground Fault Protection—Consideration shall be
established quality system to ensure all modules manufactured given to the grounding scheme, to minimize arcing and
meet a basic level of quality from a fire safety standpoint.
potential current pathways between live parts and ground
Sourcesofdcarcingshallbegivenspecificattention,aswellas potential.
any material or process steps critical to module operating
8.2 Operating Temperature:
temperature.
8.2.1 The operating temperature of a PV module is highly
7.4.3 Installation Guide—Any limitations on installation
dependent upon the installation location and installation meth-
locationorconditionscriticaltothesafeoperatingstateofaPV
ods used.
system shall be indicated in the Installation Guide. This may
8.2.2 The design of a PV system shall be such that the
include ambient conditions, mounting configuration, wiring
operating temperatures of the PV modules and all components
requirements, over-current protection devices and fuse ratings.
fall within the rated values. Materials suitable for the installa-
tion location and operating temperatures under both normal
8. PV Systems
and fault conditions (such as shading and reverse current) shall
8.1 System Design Considerations: be used.
8.2.3 Do not allow concentrated sunlight to fall on the
8.1.1 Series Fuse Protection—In most cases where two
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