173 汇流箱与配电箱
汇流箱的工况是户外加带电
汇流箱装在户外方阵中间，内部有直流高压（1000 V 或 1500 V），外部承受日晒雨淋。
这组合很棘手：既要电气绝缘，又要户外耐候，还要阻燃——三个要求互相牵制。
阻燃剂往往降低耐候性，耐候剂往往影响阻燃，配方要专门平衡。
箱体材料的两种选择
金属箱体（不锈钢或镀锌板喷塑）——屏蔽好、强度高、但要接地、要防锈、重量大。塑料箱体（阻燃 PC 或耐候 PA66-GF20）——绝缘免接地、不生锈、重量轻 60%、一次成型，但强度和屏蔽弱。组串式和微型汇流箱几乎全走塑料，大电流集中式仍走金属。
现场还原：海边汇流箱的开盖检查
2025 年 4 月，福建一个沿海渔光互补项目做年度开盖检查，某品牌的汇流箱抽检发现：箱体完好，但内部接线端子座表面有白色结晶和轻微碳化痕。业主的运维群里把照片一发，设备厂商的工程师连夜赶了过去。
现场条件：海边高盐雾、箱内昼夜温差大、凝露频繁。端子座料是普通阻燃 PA66，CTI 350，V-0 都合规——但盐雾环境里，盐分沉积加凝露，表面电解质浓度比内陆电站高得多，CTI 余量直接被吃光。
整改方案：端子座换高 CTI（600 V）阻燃 PA66，同时箱体密封结构加呼吸阀平衡内外压差，减少凝露。
半年后复检：结晶还在（这是环境属性，免不了），碳化痕没有新增。
渔光互补、盐碱地这些场景，是光伏材料验证的放大器——同样一张图纸，内陆电站跑十年没事，海边五年就出问题。材料的区域工况差异，在光伏这个户外为王的行业里，比任何其他行业都大。
IP65 防护靠设计不靠材料
防护等级是整箱设计的结果，不是材料属性。关键在三处：箱盖密封条（硅胶，
压缩量 25-30%）、进出线防水接头（PG 或 M 型，IP68 级）、箱体本身的尺寸稳定性。
PA66 吸湿膨胀会影响密封槽尺寸，潮湿地区优先阻燃 PC（吸湿率 0.1%）。
阻燃与耐候的平衡
汇流箱要 UL94 V-0 或 5VA，同时要户外 25 年。
溴系阻燃剂在紫外下会分解释放酸性物质，加速材料降解，所以户外阻燃件必须走无卤阻燃体系。
无卤阻燃 PA66 或 PC 加耐候三件套，是汇流箱箱体的标准配置，虽然贵但别无选择。
深一层：IP65 是设计出来的，不是材料赋予的
汇流箱聊防护等级，先把一个误解拆掉：IP65 是整机测试结论，不是材料参数。塑料壳体本身不防不防水的，防不防水看三道工序的配合。
第一道是密封圈设计：压缩量、截面形状、材料（EPDM 或硅胶）的老化寿命——密封圈失效汇流箱直接变鱼缸。第二道是接合面结构：平面贴合靠螺栓压紧密封圈，止口结构自带定位和限位，精度差的模具做不出稳定 IP65。
第三道是透气平衡：昼夜温差大，箱内气体胀缩呼吸，硬密封不透气会把水汽「吸」进去——呼吸阀或透气膜解决这一条，这是很多箱体早期失效的真凶。
材料在这一套里承担的是「让设计可执行」：PA66-GF30 的刚性撑住螺栓不压溃、蠕变小让压紧力十年不松、耐候让壳体自身不先粉化。料差一点，密封结构的精度保持就差一点，IP 等级就从「设计 65」滑向「现场 55」。
还有一个容易忽略的组合项：壳体料和密封圈的相容性。某些阻燃体系会加速 EPDM 老化，密封圈提前变硬失效，整机测试通过了、三年后照样渗水——这类问题要做材料组合的老化匹配试验才能提前暴露。
内部绝缘件的要求更高
箱体内部的绝缘隔板、端子座、导轨件，电气要求比外壳更高。
CTI ≥ 400 V 是硬指标，直流系统对耐电痕化的要求比交流更严——直流电场下电痕化发展更快。
内部件走高 CTI 的 PBT 或专用 PA66，外壳可以用普通阻燃料，内外不是同一种料。
高温是实际杀手
户外汇流箱在夏季正午，箱内温度可达 75-85℃，加上内部元件发热可能到 95℃。
塑料件在这个温度下长期工作，热老化速度是常温的数倍。必须按 90℃ 做热老化验证，并且箱体要设计通风散热或遮阳。
很多汇流箱失效其实是热设计不足，不是材料问题。
工程实测：4 条强制测试
测试1：热老化 90℃ 1000 h。无卤阻燃 PC 拉伸保持 88%，溴系阻燃 PC 降至 62%——户外阻燃必须无卤。
测试2：CTI。内部绝缘件 CTI ≥ 400 V，外壳 CTI 250 V 即可——内外不同料。
测试3：IP65 淋雨。硅胶密封压缩 25-30% 通过 IP65，压缩 15% 渗水——密封设计是关键。
测试4：吸湿尺寸。PA66 吸湿膨胀 0.35%，阻燃 PC 0.1%——潮湿地区箱体优先 PC。
追问三连：采购最常问的三件事
一问：汇流箱壳体走塑料还是钣金。 钣金喷涂是传统主流，成本低强度高；工程塑料（阻燃 PA66 或 PC 合金）胜在不锈不腐、一次成型、绝缘免接地。盐雾和重工业污染区塑料优势明显，内陆常规项目钣金依旧能打。价格战激烈的年代，塑料壳的综合成本优势在扩大。
二问：阻燃和耐候怎么同时满足。 户外带电箱体是「阻燃加耐候加 CTI」三重要求的典型：无卤阻燃体系加耐候三件套加高 CTI 填料的复合配方，市面上成熟牌号不多，选型时让供应商同时出示三份对应报告，缺一份就换一家。
三问：内部绝缘件为什么要比壳体高一档。 壳体只隔环境，内部绝缘件直接面对带电体：CTI 要求更高、长期工作温度更接近导体发热区、还有端子压接的机械应力。同一个箱子里，壳体料和绝缘件料通常是两种牌号，成本上别在这里省——壳体坏了换个壳，绝缘件坏了烧一个箱。### 算一笔材料账：箱体的环境系数
汇流箱这类户外带电箱体，材料账的核心变量是环境系数——同一只箱体在不同环境里的失效概率能差一个数量级。
以内部端子座为例：内陆干燥环境十年失效率按千分之一计，海边盐雾环境按百分之二计，渔业光伏水面电站按百分之五计。环境系数差五十倍。
材料升级的成本是固定的：端子座换高 CTI 牌，单只多 1.5 元，一万只箱子差 1.5 万元。而这 1.5 万元在三种环境里买到的东西完全不同：内陆是锦上添花，海边是必要保险，水面电站是生死线。
所以正确的采购结构是「分环境分档」：内陆标准档、沿海高 CTI 档、特殊环境定制档。全国一张料单的做法，要么在内陆浪费钱，要么在海上赌命。
给集成商的建议是把项目地的环境参数（盐雾、湿度、日照、污染源清单）做成标准问卷，随询价发出去——环境系数搞清楚，材料档位自然落位，这个动作的成本为零，收益是把失效风险按环境定价。### 边界声明
| 工况 | 推荐材料 |
|---|
| 组串汇流箱 | 耐候阻燃 PC 或 PA66-GF20 |
| 大电流集中式 | 金属箱体 |
| 内部绝缘件 | 高 CTI PBT 或专用 PA66 |
| 密封条 | 硅胶压缩 25-30% |
| 高温地区 | 加强通风或遮阳 |
工程备忘
汇流箱量产前必须做 IP65 + 90℃ 热老化 + CTI 三项。户外阻燃必须无卤，溴系在紫外下会加速降解。
实战案例：常见踩坑与正解
踩坑一：用常规 PA66 做户外汇流箱，没加耐候体系，两年就粉化开裂。正解：光伏储能件的设计寿命是 25 年，必须走专用耐候牌号——UV 吸收剂 + HALS + 抗氧剂三件套缺一不可，并且要 3000 h 氙灯老化验证。踩坑二：只看常温强度不看湿热老化后的强度。汇流箱装在户外，湿热老化 1000 h 后强度保持率低于 70% 的料不能用。正解：拿湿热老化后的数据选料，不拿常温数据选料。踩坑三：为了过认证临时换料，换完没重新做老化验证，批量装机后集中失效。正解：换料号必须重跑全套老化，这是光伏行业的基本规矩。
反向案例：三只端子座引发的一批召回
2024 年 8 月，华中某光伏项目并网半年后，逆变器报对地绝缘阻抗异常。排查从逆变器查到汇流箱，最后定位在汇流箱内部的直流端子座：三只端子座表面碳化，绝缘电阻跌穿阈值。
扩大排查换了三板斧：全项目同批次端子座 2000 多只全部更换。
复盘结论有两个层面：直接原因是那批端子座的 CTI 实测只有 300，低于设计要求的 400——供应商换过一次注塑厂，新注塑厂用了自购的「同牌号」料，料是真的，批次 CTI 衰减是真的；
深层原因是来料只查阻燃不查 CTI，这个漏洞让问题料畅通无阻地装进了 2000 只箱体。
后来这家设备厂的 IQC 加了一条：绝缘件每批附 CTI 实测报告，季度送第三方抽测。这套流程跑下来，同等牌号的供应商报价反而降了——供应链自己会筛选，敢留痕的料，价格反而实在。
电气失效的账，从来不是坏一只件赔一只件的钱，是排查链条上每一个环节的人力。### 延伸判断：最容易被漏掉的隐性变量
汇流箱的量产事故里，有一半不是料选错了，是隐性变量没控住。第一个变量是含水率。
PA 系材料出厂含水率、干燥条件、注塑前的存放时间，三者共同决定实际含水率，含水率不对，强度和外观都会变。
第二个变量是模具温度。模温低 20℃，表面浮纤和熔接痕强度可能差一倍。
第三个变量是装配后的时间。装完 24 h 和装完 30 天的扭矩、尺寸、密封压缩量都不一样。
这三个变量都不写在物性表上，但都写在失效报告里。
把这三件事写成一张表发给供应商，比打十通电话有用——汇流箱的选型沟通成本，基本都花在这几项反复确认上。
最后一组问答：三个纠结时刻的裁决
纠结一：箱体料和内部件料被采购合并询价。 拆开报：壳体和内部绝缘件的工况差一档，合并报价的结果要么壳体料贵了、要么端子座料危险了。在报价单上把两档分开列，顺便把「为什么分」用一行工况说明——这行说明常常就是客户的专业信任起点。
纠结二：客户质疑「塑料箱体不如钣金结实」。 换比较基准：不比抗冲击比十年——钣金五年开始锈点（喷涂破损处），塑料十年外观保持；不比强度比安装——免接地、免喷涂、一次成型的工序节省。结实与否是静态思维，十年运维是动态思维，把客户拉到动态视角。
纠结三：小批量项目要不要用库存的通用料顶一下。 盐雾和沿海项目坚决不顶，内陆干燥环境的小批量可顶但记录在案。箱体件出问题的时间尺度是三到五年，顶料的记忆早没了，账还在——用台账管住「顶一下」的冲动。### 补记：三个现场判断信号
信号一：端子座表面结晶加碳化点。 环境电解质加 CTI 不足的组合，结晶擦得掉，碳化擦不掉——有碳化痕的整批换，别只换看得见的。
信号二：箱体内壁挂水珠。 凝露管理失败，先查呼吸阀和密封圈，再查壳体温差的结露位，材料问题排最后。
信号三：密封圈提前发硬开裂。 查和壳体料的相容性，换密封圈材料比换壳体便宜得多，但验证要重做。### 验证顺序：三步走完再下单
第一步，定环境档：按项目地盐雾湿度定箱内件材料档，环境问卷随项目走。
第二步，验密封体系：壳体、密封圈、呼吸阀组合老化，IP 等级按老化后复测。
第三步，验电气件：端子座 CTI 按环境系数取档，湿热后数据为准。三步走完，箱体这个「户外小电站」才配得上十年免维护的设计初衷。
结语
前两天接了个电话——选料这件事，越早问越省事。
这类件的选料与试模，可以一起聊。
173 Junction Box and Distribution Box
The operating condition of the combiner box is outdoor with live electricity
The combiner box is installed in the middle of the outdoor array, containing DC high voltage (1000 V or 1500 V) inside, and exposed to sunlight and rain outside.
This combination is tricky: it needs electrical insulation, outdoor weather resistance, and flame retardancy—all three requirements constrain each other.
Flame retardants often reduce weather resistance, and weathering agents often affect flame retardancy, so the formulation needs to be specially balanced.
Two choices of box materials
Metal enclosures (stainless steel or galvanized sheet with plastic coating) — good shielding, high strength, but need grounding, rust protection, and are heavy. Plastic enclosures (flame-retardant PC or weather-resistant PA66-GF20) — insulated and do not require grounding, rust-proof, 60% lighter, and can be molded in one piece, but have weaker strength and shielding. String-type and micro combiner boxes are almost all made of plastic, while high-current centralized ones still use metal.
On-site Restoration: Inspection of the Junction Box Lid by the Sea
In April 2025, during the annual lid-opening inspection of a coastal fishery-photovoltaic complementary project in Fujian, a random inspection of a certain brand's combiner box found: the box was intact, but the surface of the internal wiring terminal block had white crystals and slight carbonization marks. Once the photos were posted in the owner's operation and maintenance group, the equipment manufacturer's engineers rushed over overnight.
On-site conditions: high salt fog by the sea, large diurnal temperature differences inside the box, and frequent condensation. The terminal base material is regular flame-retardant PA66, CTI 350, V-0 all compliant — but in a salt fog environment, salt deposition combined with condensation results in surface electrolyte concentrations much higher than inland power plants, and the CTI margin is directly consumed.
Rectification plan: Replace the terminal block with high CTI (600 V) flame-retardant PA66, and at the same time, add a breather valve to the enclosure sealing structure to balance the internal and external pressure difference and reduce condensation.
Re-examination after half a year: Crystallization is still present (this is an environmental attribute, unavoidable), no new carbonization marks.
Scenes like fishing-solar complementarity and saline-alkali land are amplifiers for photovoltaic material verification—using the same blueprint, a power station inland can run for ten years without issues, while one by the sea may encounter problems in five years. Regional differences in material operating conditions are greater in the photovoltaic industry, where outdoor conditions dominate, than in any other industry.
IP65 protection relies on design, not materials
The protection level is the result of the overall box design, not the material properties. The key lies in three places: the lid gasket (silicone,
Compression ratio 25-30%, waterproof cable glands for incoming and outgoing lines (PG or M type, IP68 rated), and the dimensional stability of the enclosure itself.
Moisture absorption and expansion of PA66 can affect the dimensions of sealing grooves. In humid areas, flame-retardant PC (moisture absorption 0.1%) is preferred.
Balance between flame retardancy and weather resistance
The combiner box must be UL94 V-0 or 5VA, and it should also last 25 years outdoors.
Brominated flame retardants decompose under ultraviolet light to release acidic substances, accelerating material degradation, so outdoor flame-retardant components must use a halogen-free flame retardant system.
Halogen-free flame-retardant PA66 or PC with weather-resistant three-piece set is the standard configuration for the junction box enclosure; although expensive, there is no other choice.
A deeper look: IP65 is designed, not something granted by the material.
Talking about the protection level of the combiner box, let's first clear up a misunderstanding: IP65 is the test result of the whole device, not a material parameter. The plastic enclosure itself is not waterproof; whether it is waterproof depends on the coordination of three process steps.
The first point is the design of the sealing ring: compression, cross-sectional shape, material (EPDM or silicone) aging lifespan—if the sealing ring fails, the junction box directly turns into a fish tank. The second point is the structure of the mating surface: flat surfaces fit together and the sealing ring is pressed by bolts, while the stop structure provides positioning and limit; a mold with poor precision cannot produce stable IP65.
The third point is ventilation balance: with large temperature differences between day and night, the gas inside the box expands and contracts like breathing. A tightly sealed, non-ventilated box will 'suck' in moisture — a breathing valve or venting membrane solves this issue. This is the true culprit behind the early failure of many boxes.
In this set, the material plays the role of 'making the design executable': the rigidity of PA66-GF30 holds the bolts without crushing, its low creep ensures the clamping force does not loosen for ten years, and its weather resistance prevents the housing from deteriorating first. If the material is slightly off, the precision of the sealing structure is slightly affected, and the IP rating will slide from 'designed 65' to 'actual 55'.
There is another easily overlooked combination factor: the compatibility between the casing material and the seal ring. Some flame-retardant systems can accelerate the aging of EPDM, causing the seal ring to harden and fail prematurely. The complete product might pass tests, but three years later, it still leaks — these kinds of issues can only be exposed in advance through aging compatibility tests of material combinations.
The requirements for internal insulation parts are higher
The insulation partitions, terminal blocks, and guide rails inside the enclosure have higher electrical requirements than the shell.
CTI ≥ 400 V is a strict requirement, and DC systems have stricter requirements for tracking resistance than AC systems — tracking develops faster under a DC electric field.
Internal components use high CTI PBT or specialized PA66, the casing can use ordinary flame-retardant material, the inside and outside are not the same material.
High temperature is the real killer
Outdoor junction boxes can reach temperatures of 75-85°C at noon in summer, and with the heat generated by internal components, the temperature may reach 95°C.
Plastic parts working at this temperature for a long time will age thermally at a rate several times that at room temperature. Thermal aging verification must be carried out at 90°C, and the enclosure should be designed with ventilation for heat dissipation or sun shading.
Many combiner box failures are actually due to insufficient thermal design, not material problems.
Engineering field measurement: 4 mandatory tests
Test 1: Thermal aging at 90℃ for 1000 hours. Halogen-free flame-retardant PC retains 88% tensile strength, while brominated flame-retardant PC drops to 62% — outdoor flame retardancy must be halogen-free.
Test 2: CTI. Internal insulation CTI ≥ 400 V, outer casing CTI 250 V is sufficient — different materials for inside and outside.
Test 3: IP65 Rain Test. Silicone seal compressed 25-30% passed IP65, compressed 15% leaked water—seal design is key.
Test 4: Moisture absorption dimensions. PA66 absorbs moisture and expands by 0.35%, flame-retardant PC by 0.1% — in humid areas, PC is preferred for enclosures.
Three Consecutive Follow-up Questions: The Three Most Common Questions in Procurement
Question: Should the junction box casing be made of plastic or sheet metal? Sheet metal with coating is the traditional mainstream, low cost and high strength; engineering plastics (flame-retardant PA66 or PC alloy) have the advantages of being rust-proof and corrosion-resistant, can be formed in one piece, and provide insulation without grounding. In areas with salt spray and heavy industrial pollution, plastics have clear advantages, while for conventional inland projects, sheet metal is still viable. In an era of intense price competition, the overall cost advantage of plastic casings is expanding.
Second Question: How to meet both flame retardancy and weather resistance. Outdoor live electrical enclosures are a typical example requiring 'flame retardancy, weather resistance, and CTI' simultaneously: a composite formulation of halogen-free flame-retardant system, weather resistance trio, and high CTI filler. There are not many mature grades on the market. When selecting, have the supplier provide three corresponding reports at the same time, and if any one is missing, switch to another supplier.
Three questions: Why should the internal insulating parts be rated one level higher than the enclosure? The enclosure only isolates the environment, while the internal insulating parts are directly facing live components: CTI requirements are higher, the long-term operating temperature is closer to the conductor heating area, and there is also mechanical stress from terminal crimping. In the same box, the materials for the enclosure and the insulating parts are usually two different grades, so don’t save costs here—if the enclosure fails, you can replace the enclosure; if the insulating parts fail, the whole box could burn. ### Let’s do a materials account: the environmental factor of the box.
For outdoor live boxes like combiner boxes, the core variable in material accounting is the environmental factor—the failure probability of the same box can differ by an order of magnitude in different environments.
Taking the internal terminal block as an example: the ten-year failure rate in inland dry environments is calculated at one per thousand, in coastal salt spray environments at two percent, and in fishery photovoltaic floating power stations at five percent. The environmental factor differs by fifty times.
The cost of material upgrades is fixed: replacing the terminal blocks with a higher CTI brand costs 1.5 yuan more per piece, a difference of 15,000 yuan for ten thousand pieces. And this 15,000 yuan buys completely different things in three different environments: inland it is a luxury, by the seaside it is necessary insurance, and for floating power stations it is a matter of life and death.
So the correct procurement structure is 'divided by environment and category': standard inland category, high CTI coastal category, and customized category for special environments. Using a single material list nationwide either wastes money inland or risks lives at sea.
The advice to integrators is to make a standard questionnaire of the environmental parameters of the project site (salt spray, humidity, sunlight, list of pollution sources) and send it out whenever requesting quotes — once the environmental factors are clarified, the material specifications naturally fall into place. The cost of this action is zero, and the benefit is pricing the failure risk according to the environment. ### Boundary Statement
| Operating condition | Recommended materials |
|---|
| String Combiner Box | Weather-resistant flame-retardant PC or PA66-GF20 |
| High-current centralized | Metal enclosure |
| Internal insulation component | High CTI PBT or specialty PA66 |
| Seal strip | Silicone compression 25-30% |
| High-temperature area | Enhance ventilation or provide shade |
Engineering Memo
Before mass production of the combiner box, three tests must be conducted: IP65, 90°C thermal aging, and CTI. Outdoor flame retardant must be halogen-free, as bromine compounds will accelerate degradation under UV exposure.
Practical Case Study: Common Pitfalls and Correct Solutions
Pitfall 1: Using standard PA66 for outdoor junction boxes without adding a weather-resistant system, resulting in chalking and cracking within two years. The correct approach: The design life of photovoltaic storage components is 25 years, so special weather-resistant grades must be used — the trio of UV absorbers, HALS, and antioxidants is indispensable, and a 3000-hour xenon lamp aging test must be conducted. Pitfall 2: Only considering room temperature strength without looking at strength after humid heat aging. If the junction box is installed outdoors, materials whose strength retention is below 70% after 1000 hours of humid heat aging cannot be used. The correct approach: Select materials based on data after humid heat aging, not room temperature data. Pitfall 3: Temporarily changing materials to pass certification without redoing aging verification, leading to concentrated failures after mass installation. The correct approach: When changing material grades, a full set of aging tests must be rerun — this is a basic rule in the photovoltaic industry.
Reverse Case: A Batch Recall Caused by Three Terminal Blocks
In August 2024, six months after a photovoltaic project in central China was connected to the grid, the inverter reported an abnormal ground insulation resistance. The investigation traced the issue from the inverter to the combiner box and finally located it at the DC terminal block inside the combiner box: the surfaces of three terminal blocks were carbonized, and the insulation resistance fell below the threshold.
Expanded inspection with three new measures: all more than 2,000 terminals of the same batch across the entire project were replaced.
There are two levels of conclusions from the review: the direct cause is that the CTI of that batch of terminal blocks was only 300 in actual testing, lower than the design requirement of 400 — the supplier had changed the injection molding factory once, and the new factory used self-purchased material of the "same grade"; the material was real, and the batch's CTI degradation was indeed true;
The deeper reason is that the incoming materials are only checked for flame retardancy and not for CTI, and this loophole allowed the problematic materials to be installed into 2,000 enclosures without obstruction.
Later, the IQC of this equipment factory added a rule: each batch of insulating parts must be accompanied by an actual CTI test report, and every quarter a third-party sampling test is conducted. After running through this process, the quotes from suppliers of the same grade actually decreased—the supply chain will self-filter, and materials that leave traceable records actually become reasonably priced.
The cost of electrical failure has never been about paying for each faulty part; it is the manpower involved in checking every link in the chain. ### Extended judgment: The hidden variables most likely to be overlooked
In mass production accidents of the combiner box, half are not due to the wrong material selection, but because hidden variables were not controlled. The first variable is moisture content.
The factory moisture content of PA series materials, drying conditions, and storage time before injection molding together determine the actual moisture content. If the moisture content is incorrect, both strength and appearance will change.
The second variable is the mold temperature. When the mold temperature is 20°C lower, the surface float fibers and weld line strength may differ by a factor of two.
The third variable is the time after assembly. The torque, dimensions, and seal compression amount are different at 24 hours after assembly and 30 days after assembly.
These three variables are not listed on the material properties table, but they are all included in the failure report.
Write these three things in a table and send it to the supplier; it's more useful than making ten phone calls—the communication cost for selecting the junction box is basically spent on repeatedly confirming these items.
The final Q&A: The verdict on three moments of dilemma
Dilemma 1: The materials for the enclosure and the internal components were combined in a procurement inquiry. If quoted separately: the operating conditions for the enclosure and the internal insulation parts differ by one level, and the result of a combined quote would either make the enclosure material too expensive or put the terminal base material at risk. On the quotation form, list the two levels separately and, while at it, use one line to explain 'why they are separated'—this line of explanation is often the starting point for the customer's professional trust.
Dilemma Two: The customer questions, 'Plastic cases are not as sturdy as sheet metal.' Change the comparison benchmark: Don't compare impact resistance over ten years — sheet metal starts to rust after five years (at points where the coating is damaged), while plastic maintains its appearance for ten years; don't compare strength, compare installation — grounding is unnecessary, painting is unnecessary, and the one-step forming process saves labor. Sturdiness is a static way of thinking, while ten-year operation and maintenance is a dynamic way of thinking, so shift the customer to a dynamic perspective.
Dilemma 3: Whether to use stock common materials for small-batch projects. Salt-spray and coastal projects definitely should not use them, while small batches in dry inland environments can use them but must be recorded. The time scale for problems with enclosure parts is three to five years; the memory of using substitute materials is long gone, but the records remain—use a ledger to control the impulse to 'just use a substitute.' ### Note added: Three on-site judgment signals
Signal 1: Crystallization and carbonization spots on the surface of the terminal block. The combination of environmental electrolytes and insufficient CTI causes it; the crystallization can be wiped off, but the carbonization cannot — replace the entire batch with carbonization marks, don’t just replace the visible ones.
Signal 2: Water droplets hanging on the inner wall of the box. Condensation management has failed. First, check the breather valve and sealing ring, then check the condensation spots caused by temperature differences in the housing, and consider material issues last.
Signal 3: The sealing ring hardens and cracks prematurely. Check the compatibility with the housing material; changing the sealing ring material is much cheaper than changing the housing, but the validation needs to be redone. ### Validation sequence: complete the three steps before placing the order
Step one, set the environmental file: determine the materials inside the box according to the project's site salt spray and humidity levels, and the environmental questionnaire follows the project.
Step two, check the sealing system: age the housing, seal ring, and breather valve combination, and retest the IP rating after aging.
Step three, test the electrical components: the terminal block CTI is selected according to the environmental coefficient, and the data after damp heat testing is used as the standard. Only after completing these three steps does the enclosure of this 'small outdoor power station' live up to the original design intention of ten years of maintenance-free operation.
Conclusion
I received a call a couple of days ago—when it comes to choosing materials, the earlier you ask, the less trouble it is.
The material selection and mold trial for this type of part can be discussed together.
