1、Designation: E2908 12Standard Guide forFire Prevention for Photovoltaic Panels, Modules, andSystems1This standard is issued under the fixed designation E2908; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisio
2、n. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide describes basic principles of photovoltaicmodule design, panel assembly, and system installation toreduce the risk of f
3、ire originating from the photovoltaic sourcecircuit.1.2 This guide is not intended to cover all scenarios whichcould lead to fire. It is intended to provide an assembly ofgenerally-accepted practices.1.3 This guide is intended for systems which contain pho-tovoltaic modules and panels as dc source c
4、ircuits, although therecommended practices may also apply to systems utilizing acmodules.1.4 This guide does not cover fire suppression in the eventof a fire involving a photovoltaic module or system.1.5 This guide does not cover fire emanating from othersources.1.6 This guide does not cover mechani
5、cal, structural,electrical, or other considerations key to photovoltaic moduleand system design and installation.1.7 This guide does not cover disposal of modules damagedby a fire, or other material hazards related to such modules.1.8 UnitsThe values stated in SI units are to be regardedas standard.
6、 No other units of measurement are included in thisstandard.1.9 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-b
7、ility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E772 Terminology of Solar Energy ConversionE2481 Test Method for Hot Spot Protection Testing ofPhotovoltaic Modules2.2 Other Standards and Documents:IEC 61215 Crystalline silicon terrestrial photovoltaic (PV)modu
8、lesDesign qualification and type approvalIEC 61730 Photovoltaic (PV) module safety qualificationNorth American Board of Certified Energy Practitioners(NABCEP), Study Guide for Photovoltaic System Install-ersNFPA 70 US National Electrical Code (article 690)UL 1703 Standard for Flat-Plate Photovoltaic
9、 Modules andPanelsUL 1741 Inverters, Converters, and Controllers for Use inIndependent Power Systems3. Terminology3.1 Definitions of terms used in this standard may be foundin Terminology E772.3.2 Definitions:3.2.1 ground fault, na condition where there is an unin-tended electrical connection betwee
10、n the active PV circuit andground.4. Summary of Practice4.1 Photovoltaic modules and panels should be designed tominimize the risk of fire and should be assembled with goodquality-control practices.1This test method is under the jurisdiction of ASTM Committee E44 on Solar,Geothermal and Other Altern
11、ative Energy Sources and is the direct responsibility ofSubcommittee E44.44 on Photovoltaic System Fire Safety.Current edition approved Dec. 1, 2012. Published December 2012. DOI:10.1520/E2908-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at
12、 serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.2 Photovoltaic systems should be designed to mini
13、mizethe risk of fire, and installed with fire safety in mind. Installersshould be aware of PV-related fires that have occurred and thecause of those fires.5. Significance and Use5.1 Photovoltaic modules are electrical dc sources. dcsources have unique considerations with regards to arc forma-tion an
14、d interruption, as once formed, the arc is not automati-cally interrupted by an alternating current. Solar modules areenergized whenever modules in the string are illuminated bysunlight, or during fault conditions.5.2 With the rapid increase in the number of photovoltaicsystem installations, this gu
15、ide attempts to increase awarenessof 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 require-ments. It is not intended
16、to capture all conditions or scenarioswhich could result in a fire.6. Arcing6.1 dc Arcing:6.1.1 An electrical arc can form where an electric potentialexists between two neighboring conductors. Unlike ac arcswhich may be extinguished during the alternating-cycle ofcurrent, a dc arc will be maintained
17、 indefinitely until inter-rupted. A dc arc will be sustained until the voltage potential isreduced, an arc-detection device disrupts the flow of current, orthe effective distance between the conductors becomes toolarge to sustain the arc. Even once the arc is eliminated, the arcmay have been suffici
18、ent to cause burning or ignition ofsurrounding materials.6.1.2 An arc may propagate across the surface of the module(for example, along the gap between rows of cells) as materialsare burned away.6.1.3 The arc may extinguish and re-ignite under variableenvironmental conditions or with expansion and c
19、ontraction ofaffected materials, and may also extinguish at night and restartthe next day.6.1.4 Common sources of arcs in PV modules:6.1.4.1 Cracks in solar cells (crystalline or thin film).6.1.4.2 Inadequate spacing between parts of different volt-age potentials.6.1.4.3 Improper bonding of intercon
20、nects to cells.6.1.4.4 Improper bonding of interconnects to bus bar.6.1.4.5 Improper bonding of bus bar to wiring terminal orconnector.6.1.4.6 Insufficient allowance for thermal expansion andcontraction of materials, which leads to mechanical fatigue.Common examples include cell interconnects and ex
21、pansionjoints in conduits.6.1.4.7 Insufficient strain relief between parts; especiallyfield wiring terminations, solder joints, and internal conduc-tors.6.2 ac Arcing:6.2.1 Both ac and dc circuits may be present in a solarphotovoltaic system, and both circuits contain potential arcsources. A dc arc
22、may be sustained over a larger distance andlonger duration than an ac arc due to the one-directional flowof the dc current, which is not easily interrupted. The current inan ac arc always goes to zero twice per cycle.7. PV Modules and Panels7.1 Design Against ArcingModules shall be designed toreduce
23、 the risk of arcing.7.1.1 Modules shall meet the spacing requirements of IEC61730 or UL 1703 to reduce the occurrence of arcing underboth normal operating conditions and fault conditions.7.1.2 Materials and processes used in the manufacture of PVmodules shall be designed to be durable and reliable o
24、ver theentire service life of the PV module.7.1.3 Failure mechanisms, such as mismatch of thermalexpansion coefficients, metal fatigue, corrosion or vibration,shall be considered during the selection of materials, modulelay-out, and assembly.7.1.4 Material selection shall include consideration of th
25、eoperating temperatures of the material and aging characteristicsof the material.7.2 Design for Arc and Fire Suppression:7.2.1 Materials in close contact to potential arc sources,such as junction boxes, shall have a minimum arc andflammability rating in accordance with IEC 61730 or UL 1703.This help
26、s to reduce the risk of fire in the event of an arcingevent.7.2.2 According to the 2011 National Electrical Code, anarc-detection device is required to disconnect the current flowin the event of arcing. Depending on the location of the device,it may protect an individual module or an entire string.C
27、onsideration shall be given to the reliability of such devices,to avoid nuisance trips and costly servicing.7.3 Operating Temperature:7.3.1 A PV module converts a portion of the suns energyinto electrical energy. The portion of the suns energy that isnot converted into electrical energy is either re
28、flected, trans-mitted through the module, or transformed into heat energy.Therefore, a PV module usually operates at a temperaturehotter than the surrounding ambient temperature.7.3.2 Operating Temperature ConsiderationsThe exactoperating temperature of a module, and of any given compo-nent within a
29、 module, depends on a variety of factors.7.3.2.1 Environmental FactorsWind speed, winddirection, ambient temperature, solar irradiance, and cloudcover.7.3.2.2 Installation FactorsAngle of installation, racktype, module spacing, location, wind obstructions, trackingversus non-tracking, ventilation, s
30、hading events.7.3.2.3 Module FactorsCell mismatch (leading to non-uniform heat generation), insulated sections (e.g. junctionboxes), color, framing, transparency, material thermalconductivity, thermal convection characteristics, current-carrying limits of live parts.7.3.3 ShadingShading events can c
31、ause shaded cells to actas power sinks (resistors) as opposed to power generators.E2908 122Therefore, shaded cells can run much hotter than neighboringcells. Although modules are designed to operate in un-shadedconditions, some degree of localized shading is inevitable inmost installations. Refer to
32、 Test Method E2481 for additionalinformation.7.3.3.1 The amount of heating of a cell depends on the shuntand series resistance characteristics of the shaded cells, thecurrent flowing through the cell, and whether the cells arepartially illuminated.7.3.3.2 Material CombustionMaterials in contact with
33、cells shall be able to withstand temperatures under the shadedcondition without exceeding material ignition temperatureratings. The design may be tested to assess material suitabilityper UL 1703, Section 19, Temperature Test.7.3.3.3 Modules shall have adequate protection in the eventof shading.7.3.3
34、.4 DiodesA common method for providing shadingprotection is through bypass diodes connected in parallel withthe cells to be protected. As the forward and reverse charac-teristics of a PV cell are different, the diodes shall be sized toactivate in the event of shading of part or all of one or more of
35、the cells to prevent the formation of localized hot spots. Thediodes must be able to safely handle the string current.Activation of the diode during a cell shading event shall notresult in overheating of the diode, nor materials surroundingthe diode. The diode shall be mounted and connected using ar
36、obust and reliable method, including strain relief as appropri-ate. Diode quality and the mounting method should be evalu-ated for durability. If diodes are mounted mechanically, theyshould be tested under simulated field conditions to ensure thatadequate contact is maintained over time.7.4 Document
37、ation:7.4.1 RecognitionThe module should be certified by anapproved organization to meet a minimum level of safety. Twostandards that are commonly used to assess a minimum safetylevel are UL 1703 and IEC 61730.7.4.2 Quality SystemThe PV manufacturer shall have anestablished quality system to ensure
38、all modules manufacturedmeet a basic level of quality from a fire safety standpoint.Sources of dc arcing shall be given specific attention, as well asany material or process steps critical to module operatingtemperature.7.4.3 Installation GuideAny limitations on installationlocation or conditions cr
39、itical to the safe operating state of a PVsystem shall be indicated in the Installation Guide. This mayinclude ambient conditions, mounting configuration, wiringrequirements, over-current protection devices and fuse ratings.8. PV Systems8.1 System Design Considerations:8.1.1 Series Fuse ProtectionIn
40、 most cases where two ormore strings of photovoltaic modules are connected in parallel,the branch or sub-string shall be protected by a fuse. The fuseprotects the modules and other electrical components in thesystem from over-current in the event of a fault condition. Thetotal available current and
41、fuse rating shall not exceed thatrecommended by the module or panel manufacturer.8.1.2 Module-to-Module ConnectionsAll wiring and con-nectors used shall be of the type and sizing recommended bythe module manufacturer and in accordance with local codes.Wiring shall be suitable for the intended applic
42、ation, includingtemperature range, wire gauge, UV resistance, waterresistance, and system voltage. Consideration shall be given tothe extreme and nominal conditions expected throughout themodule lifetime. The means for connection shall be in accor-dance with the module and connector Installation Gui
43、des orany applicable local codes. Wiring shall be mechanicallysecured, if required, to prevent strain on the electricalconnections, with adequate slack to allow for thermal expan-sion and contraction of the wiring.8.1.3 Other WiringAll other wiring in the PV system shallbe suitable for the intended
44、application and secured if required,with consideration given to the same factors as described formodule-to-module wiring. Wiring securement means must beable to withstand outdoor conditions, including UV radiation,over the expected service life of the system, and should bechecked routinely as part o
45、f regular system maintenance. Ifwiring is in metallic conduit, particular attention should begiven to proper installation and wire management techniques toreduce the possibility of ground faults.8.1.4 dc Disconnectsdc disconnects shall be used to allowsafe disconnection of a dc string from an invert
46、er, combinerbox, charge controller or other electrical components in thesystem. The disconnect shall be rated appropriately for the dccurrent and voltage of the system, in accordance with localcodes. Note that an ac-only disconnect may or may not besuitable for a dc circuit, as it relies on the alte
47、rnating-nature ofac current to disrupt the current flow.8.1.5 InvertersInverters shall be appropriately sized forthe intended location, be approved to the local standard, suchas UL 1741, and meet local code requirements for connectionto the grid. Inverters may have built-in arc-detection capability,
48、which disconnects the system in the event of an arc to reducedamage to the system and supporting structures.8.1.6 Ground Fault ProtectionConsideration shall begiven to the grounding scheme, to minimize arcing andpotential current pathways between live parts and groundpotential.8.2 Operating Temperat
49、ure:8.2.1 The operating temperature of a PV module is highlydependent upon the installation location and installation meth-ods used.8.2.2 The design of a PV system shall be such that theoperating temperatures of the PV modules and all componentsfall within the rated values. Materials suitable for the installa-tion location and operating temperatures under both normaland fault conditions (such as shading and reverse current) shallbe used.8.2.3 Do not allow concentrated sunlight to fall on themodules, unless explicitly permitted by the PV manufacturer.8.2.4 Mount t
