Guide to Procurement and Installation of Combiner Box Housings for Photovoltaic Projects – Essential Reading for EPC Contractors

This article covers the following content

This article is aimed at photovoltaic EPC general contractors, project installation teams, and procurement personnel, helping you quickly grasp the key points of purchasing and installing photovoltaic combiner box casings in 15 minutes:

1. 5 key installation details - Location selection, incoming line orientation, grounding and lightning protection, acceptance checklist

2. Comparison of 25-year life cycle costs - Why are the cheapest options actually more expensive?

3. OEM customization capabilities - Four customization dimensions: opening, silkscreen printing, color, and size

4. 6 common procurement misconceptions - IP rating, material selection, customization process, etc.

5. Procurement Action Guide - Download materials, get a quote, and request samples.

This article was written by the BSUMWELL technical team. We are a source manufacturer specializing in photovoltaic combiner box housings. Our products cover materials such as UV-resistant PC, SMC fiberglass, and 304/316 stainless steel. All series come standard with IP65 protection rating and we support OEM customization.

1. Five key details for on-site installation of photovoltaic combiner boxes: location, sealing, grounding, and acceptance.

Even the best junction box enclosure is useless if it's not installed properly; an IP65 protection rating is just empty talk. Every small oversight during installation can lead to water ingress, corrosion, or even equipment burnout a few years later.

The following five details are where problems are most likely to occur during the on-site installation of photovoltaic projects.

1.1 Installation Location Selection – Avoiding the awkward situation of “sufficient protection level, but wrong location”

IP65 can protect against heavy rain and sandstorms, but it is not waterproof. If the installation location is chosen incorrectly, even the highest protection rating will be useless.

Five principles for selecting an installation location:

1. Avoid low-lying areas prone to water accumulation: After heavy rain, the ground will accumulate water in a short period of time, which IP65 cannot withstand. If the project site is in an area with high rainfall and low terrain, either install the junction box in a higher position (more than 1 meter off the ground) or consider upgrading the protection level.

2. Try to avoid direct sunlight: Although the casing itself has UV resistance, prolonged exposure to sunlight will accelerate the aging of the sealing strips and materials. Choosing a location with natural shade (such as the back of the component or below the equipment) can effectively extend the life of the casing.

3. Reserve maintenance space: At least 800mm of operating space should be reserved in front of the opening direction of the junction box. Many projects install the junction box in a small space, making it impossible to even open the door during operation and maintenance—this is a common oversight in the design phase.

4. Confirm the support load-bearing capacity: Metal and SMC casings are quite heavy, so it's necessary to confirm the structural load-bearing capacity of the bracket or column before installation. A box weighing over 10kg hanging on a flimsy bracket may loosen or even fall under long-term wind loads.

5. Keep away from high-temperature heat sources: The combiner box itself is already generating heat. If there is an inverter's heat dissipation vent or a transformer nearby, the heat will be added on top of the heat, which will shorten the lifespan of the casing and components.

Our technical team can provide installation location assessment advice to help EPC contractors avoid these potential problems during the project design phase.

1.2 Inlet Orientation and Sealing – The Final Step in Waterproofing Success

Protection ratings are designed in, but they are also "implied." If the cable entry point and sealing are not done properly, IP65 is just a white label.

Install with the cable inlet facing downwards

This is the most basic waterproofing principle: the cable inlet should face downwards to prevent water from flowing into the enclosure along the cable. If site conditions necessitate a side entry, the cable must be inspected before entering the enclosure.Drip Loop—Let the water drip at the lowest point, rather than sliding down the cable into the enclosure.

Correct installation of Cable Gland

Cable glands are the most prone to problems. The following three points must be observed:

• The sealing ring must match the outer diameter of the cable: If the cable is too loose, water will seep in; if it's too tight, the cable will be damaged. The actual measured cable diameter should be used as the reference when selecting a cable.

• Tighten to the recommended torque: Insufficient torque will result in a poor seal, while excessive torque will cause the sealing ring to be squeezed out and deformed. General reference values: M20 Cable Gland tightening torque is approximately 2.5-3.5 N·m, and M25 is approximately 4.0-5.5 N·m (slight differences may occur between different brands/materials. When installing, the standard for judgment is that the sealing ring is evenly compressed and the cable is not loose. It is recommended to use a torque wrench to avoid estimating by feel).

• Unused cable inlets must be sealed with waterproof plugs: A single unsealed hole can render an entire IP65 rating invalid. On-site, it's common to see workers "forgetting to seal" or "losing the plug"—a plug costing only a few dollars can save you the cost of equipment worth tens of thousands of dollars.

Common mistake: Insufficient cable bending radius

Large-section DC cables (such as 10mm²-16mm² PV Wire) are inherently rigid. If they make a sharp turn immediately after exiting the cable gland, the cable will exert continuous lateral stress on the gland. Over time, this will cause the sealing ring to deform and the waterproofing to fail.

Our photovoltaic casings come pre-installed with cable inlet locations, cable glands, and waterproof plugs, eliminating the need for additional drilling on-site—saving time and preventing damage to the anti-corrosion layer from on-site drilling. All accessories are pre-installed, so there's no issue of "forgetting to buy a plug."

1.3 Grounding and Lightning Protection – Special Requirements for Metal Enclosures

Plastic casings (PC/SMC) are insulators and do not require grounding. Metal casings (stainless steel/metal) are conductors and must be reliably grounded—this is a bottom line for life safety, not an option.

Three key points for grounding metal casings:

• Grounding resistance ≤4Ω: (According to NEC 250.4(A)(1), non-current-carrying metallic components of electrical systems are required to be reliably grounded to ensure the safe discharge of fault current.) After installation, a grounding resistance tester must be used to verify the connection; it cannot be assumed that the connection is secure.

• The casing must have clear grounding markings and grounding terminals. — It is convenient for installers to identify and also convenient for acceptance inspection.

• Lightning protection grounding and protective grounding must be installed separately. — The junction box contains an SPD (surge protector), whose grounding and the outer casing protective grounding belong to different circuits and should not be mixed.

Why is the grounding requirement stricter for photovoltaic DC systems than for AC systems?

DC arcs do not cross zero, and once they start, they are difficult to extinguish on their own. If the casing is energized, touching it by maintenance personnel could trigger a DC arc—which is more dangerous than an AC electric shock. Therefore, the metal casing must be grounded to ensure that it does not become energized under any fault conditions.

Our metal photovoltaic casings come standard with grounding terminals and grounding markings, meeting UL/NEC grounding requirements. The SMC and PC series require no grounding treatment, saving labor and materials. The amount of grounding work required is also a factor to consider when choosing between stainless steel and plastic.

1.4 Post-installation acceptance checklist

The combiner box is installed, but don't rush off. Take 5 minutes to go through this checklist; it will save you the trouble of having to come back and redo it later.

Photovoltaic combiner box installation acceptance checklist

For the complete "Photovoltaic Combiner Box Installation and Acceptance SOP", please contact customer service.

2. Comparison of 25-year life cycle costs of photovoltaic combiner box casings – PC, SMC, and stainless steel: which is more cost-effective?

When procuring photovoltaic projects, we should not only look at "how much money is spent today", but also "how much money will be spent in total over 25 years".

The purchase price of a single casing may differ by only a few hundred dollars, but over 25 years, choosing the wrong one could cost tens of thousands of dollars more.

2.1 Unit Purchase Price vs. Total Cost Over 25 Years – A Table to Understand the Difference

Notes:

• While PC enclosures are typically evaluated for replacement every 10-15 years, not all projects require replacement. If the project operates in a mild environment and is properly sealed and maintained, the PC enclosure may well last up to 25 years without needing replacement. The table above represents a conservative estimate; actual needs should be assessed based on the specific circumstances of each project.

• The above are general industry estimates; actual costs vary depending on project size, installation conditions, local labor rates, and other factors. For cost estimates tailored to specific projects, please contact our technical team for customized analysis.

Three sentences to understand this table:

1. PC cases: They're cheap when you buy them, but they might become expensive over time. The initial purchase cost is the lowest, but if the project requires replacement even once, the total cost will exceed that of SMC.

2. SMC casing: It's a bit pricey when you buy it, but it's worry-free to use. The initial cost is 30-50% higher than that of a PC, but it doesn't need to be changed for 25 years, so the total cost over the entire life cycle is actually lower.

3. Stainless steel casing: It's the most expensive when you buy it, but it saves the most money. It has the highest initial cost, but requires zero maintenance, zero replacement, and zero power generation loss, making it the preferred choice for large-scale ground-mounted power plants.

2.2 The Real Cost of Replacing the Shell Mid-Process—It's Not Just "Buying Another One"

Many procurement teams only calculate "how much the outer casing costs" and forget to calculate "how much it would cost to replace the outer casing".

A realistic cost breakdown:

Suppose a ground-mounted power station has a junction box whose outer casing cracked in its 12th year of operation and needs to be replaced.

Note: The above are general estimates for reference only. Actual costs vary depending on factors such as project size, geographical location (due to differences in labor costs), and construction difficulty. Large power plants may experience higher power generation losses, while labor costs may account for a larger proportion of costs in smaller projects. For specific calculations, please contact us for a detailed cost analysis tailored to your project.

In conclusion: An initial casing costing 500 yuan can have a total cost of 5,000-10,000 yuan if replaced once in the future. A cheap casing will not be cheap if it needs to be replaced after 10 years.

Our SMC and stainless steel series casings are designed to last the same lifespan as a solar power plant (25 years), fundamentally avoiding the hidden costs of mid-life replacements. A little more upfront, but 25 years of worry-free ownership. [Learn more about SMC/Stainless Steel Series Products]

3. OEM Customization of Photovoltaic Combiner Box Shells – Four Dimensions: Openings, Silk Screen Printing, Colors, and Sizes

Each photovoltaic project has a different combiner box configuration—different component brands, different incoming line directions, and different owner brand colors. Our customization service covers four types of needs.

3.1 Detailed Explanation of the Four Customization Dimensions

Custom-made openings are the most common requirement, but also the most easily overlooked value. On-site opening is not only time-consuming but can also damage the casing's anti-corrosion layer and sealing structure. Our custom service pre-drills the holes at the factory, allowing for direct on-site installation—saving a step and reducing potential problems. [Click to submit your customization request]

3.2 Customization Process and Delivery Time

Customization process:

Requirements communication → Drawing confirmation → Sample making → Customer confirmation → Mass production

Delivery time reference:

• Minimum order quantity：

• Standard customization (silk screen printing, perforation, color): No minimum order quantity required.

• Fully custom molds: Minimum order quantity needs to be assessed.

• Sample Policy：

• Customized samples can be provided to confirm the effect, and the sample cost can be deducted from the bulk order.

We offer a one-stop customization service from drawings to mass production, and support small batch orders.

4. Frequently Asked Questions (FAQ) about Common Procurement Misconceptions

Q1: Is IP65 sufficient for photovoltaic applications? Should we upgrade to a higher rating?

A：For most photovoltaic projects—ground-mounted centralized, commercial and industrial rooftop, and agro-solar hybrids—IP65 is sufficient to withstand heavy rain and dust storms. IP65 protects against heavy rain but not water immersion, so installation locations should avoid low-lying areas prone to flooding. If the project is located on coastal mudflats, on floating solar panels, or in areas that may be flooded, a higher protection rating needs to be considered. Our standard products are IP65; higher rating requirements can be discussed separately.

Q2: How much more expensive is the SMC fiberglass casing compared to PC? Is it worth it?

A：The initial procurement cost of SMC is typically 30-50% higher than that of PC. However, in ground-mounted power plant scenarios, SMC's impact resistance (IK10 vs IK08) and weather resistance (25 years vs 15 years) are unmatched by PC. If the project is located in a hail-prone Gobi/desert region, SMC is a safer choice. Choosing SMC is not about "spending more money," but about "spending it wisely."

Q3: Does the stainless steel casing have to be 316? Is 304 not acceptable?

A：It depends on the project location. For inland projects more than 2 kilometers from the coastline, 304 stainless steel is sufficient. For projects within 2 kilometers of the coastline, such as floating solar power or island projects, 316 stainless steel is recommended—316 contains molybdenum, making it much more resistant to chloride ion corrosion than 304. Choosing the wrong stainless steel for a coastal project may lead to corrosion and perforation of the outer casing in 5-10 years.

Q4: Is a waterproof and breathable valve necessary? In what situations can it be omitted?

A：The core function of a waterproof and breathable valve is to balance the pressure difference between the inside and outside, expel moisture, and prevent condensation. In areas with large diurnal temperature variations (deserts, plateaus, arid inland regions), waterproof and breathable valves should be standard equipment. If the project is located in a relatively constant temperature area with small temperature differences, their inclusion can be considered on a case-by-case basis. We include breathable valves as standard equipment in our regular products, but this can be discussed during the selection process.

Q5: Buying an outer casing that's too big is wasteful, and buying one that's too small won't fit—how do I determine the internal dimensions?

A：Determining the internal dimensions of the combiner box requires three steps:

1. Calculate the dimensions of all internal components;

2. Calculate the minimum required internal space based on the component layout diagram;

3. Confirm that the creepage distance meets the requirements.

We can assist in confirming whether the internal dimensions of the enclosure meet the requirements based on the component list and layout diagram provided by the customer. For technical support, please contact customer service.

Q6: How do I request samples? How do I place a custom order?

A：Samples are available upon request. 1-2 free samples are provided for standard stock models (international shipping costs to be borne by the customer); sample costs for customized models will be assessed on a project-by-project basis and can be deducted from the bulk order cost.

Customized order process: Requirements communication → Drawing confirmation → Sample production → Customer confirmation → Mass production.

[Refer to the photovoltaic combiner box enclosure selection technical guide]

5. Procurement Action Guide – What's Next?

Thank you for reading this far. If you are working on a solar power project and need to purchase combiner box enclosures, here are three steps you can take to get started immediately:

5.1 Download Technical Documentation

[Click to enter the download center (or Contact customer service to obtain）]

5.2 Get a project quote

Please provide the following information:

• Project Types (Ground-mounted Power Stations/Commercial/Industrial/Commercial Rooftop Power Stations/Agricultural-Solar Hybrid Power Stations/Others)

• Estimated quantity

• OEM customization required (hole opening/silk screen printing/color/size)?

• Target delivery date

[Click to submit an inquiry (RFQ) Or contact sales on the right]

5.3 Request a sample

• Standard models: Free samples (shipping costs not included)

• Customized models: Project-based assessment

[Click to request a sample]

(Previous article: Completed the guide to purchasing and installing photovoltaic combiner box housings? For technical details on material comparison, IP protection, UV resistance, and heat dissipation, please read "...") Photovoltaic Power Plant Combiner Box Housing Selection Technical Guide – Materials, IP Protection, Heat Dissipation and 1500V System Design)