- All
- Product Name
- Product Keyword
- Product Model
- Product Summary
- Product Description
- Multi Field Search
Views: 106 Author: 深圳市博森威电气有限公司 Publish Time: 2026-05-11 Origin: BSUMWELL
——covering Cable Joints, Potting, And DIY Hybrid Solutions.
In the development of outdoor equipment, underwater robots, agricultural sensors, or marine electronics, a seemingly minor detail—reliably connecting thin wires (22 AWG and below) to a waterproof casing—is often the culprit that causes an entire batch of products to fail in the field.
As a factory that deals daily with IP67 enclosures, cable connectors, and sealing materials, we've seen far too many cases of rework due to improper selection or negligence in installation details. This article avoids theoretical clutter, directly providing verified, actionable solutions, operational steps, and troubleshooting checklists to help your project find the optimal balance between cost and reliability.
Over the past three years, leakage at the wire entry point has accounted for more than 60% of the customer after-sales issues we've handled. Below are some of the most recurring failure modes, which you can check against one by one during the R&D phase:
A single extremely fine wire (<3mm) cannot be compressed tightly.
The rubber bushing of a standard cable gland is typically designed for cables with an outer diameter of 4-8mm. When you use 24 AWG (approximately 1.2mm outer diameter) or smaller wires, even when the nut is fully tightened, the bushing cannot deform sufficiently, allowing water to seep in along the outer wall of the wire.
Customer Case: A customer using underwater lighting directly used PG7 connectors to encapsulate 26 AWG control wires. After a 2-hour immersion test, water entered the wires.
Multiple thin wires pass through the same entrance side by side.
Inserting two to four thin wires simultaneously into a connector bushing creates V-shaped gaps between the wires—gaps that cannot be filled by rubber compression. Even if the outer layer appears sealed, water can still seep through the gaps between the wires via capillary action. This is commonly found in sensor junction boxes and multi-signal output devices.
Manually drilled burrs to pierce O-rings
To save on mold costs, many customers drill holes in the housing using a hand drill. The burrs produced by the drill bit (especially on aluminum alloy housings) act like blades, directly cutting the O-rings or gaskets when tightening the joints, causing the surface seal to fail. Of the failed parts we've inspected, approximately 30% of the O-rings showed obvious puncture marks.
Cheap sealant cracked after being exposed to direct sunlight outdoors.
DIY tutorials often use hot melt glue or regular silicone sealant to seal gaps. However, these materials will shrink, crack, or powder when exposed to outdoor temperatures ranging from -20°C to 60°C.
Note: Even with RTV silicone, you must choose a model labeled "UV resistant" or "weather resistant".
Dynamic bending/vibration causes joint loosening
If the cable is subjected to frequent pulling or the equipment is installed on a vibration source (such as a water pump or vehicle), the nuts of ordinary nylon connectors will gradually loosen, and the sealing pressure will decrease. Anti-loosening nuts or thread-locking adhesive need to be added.
The "sucking effect" caused by temperature difference circulation
The sealed casing expands when heated during the day and contracts when cooled at night, creating a pressure difference between the inside and outside. If the wire inlet is not completely airtight, moisture can be "drawn" into the casing. This slow water ingress is often not detected until months later.
We analyzed the mainstream solutions currently on the market and found a significant gap in cost-effectiveness:
This article focuses on filling the "mid-range solution gap"—providing mature solutions with costs ranging from $3 to $25, which can be mass-produced and have protection levels of IP67-IP68. The components used are all standard industrial products or can be 3D printed/manually modified.
The table below is an internal comparison table that we often use when providing technical solutions to clients. You can use it directly for selection.
Factory Recommendation: For products in mass production that require certification, the first or third option should be prioritized. A hybrid option is suitable for R&D validation or internal tools.
Please answer the following four questions in order to confirm the recommended plan:
Must the wires be detachable (e.g., for field sensor replacement)?
Yes → Skip to question 4
No → Continue
Is the outer diameter of the wire less than 3mm (22 AWG or smaller)?
Yes → Multi-hole inserts or potting are required; standard connectors cannot be used.
No → Standard cable connectors are usually sufficient.
Are there multiple wires (≥2) that need to pass through the same entrance?
Yes → Prefer cable connectors with multi-hole inserts or separate sealing plugs.
No → A single thin wire can be thickened using heat shrink tubing to modify a standard connector.
Budget (material cost at each point of entry)?
<$5 → Hybrid DIY Solution (3D Printed TPU Bushing + Marine-Grade Sealant)
$5-15 → Cable connector + pre-made multi-hole insert
$15 and high reliability required → Modular connector (M8/M12)
This section provides specific parameters and procedures that can directly guide production line operations. All methods have been validated in our factory.
The essence of the problem:The inner diameter of the rubber bushing inside the connector (usually 6-8mm) is much larger than the outer diameter of the wire (1-1.5mm), making it impossible to generate effective compression.
Three proven solutions (in recommended order):
Option 1A: Double-layer adhesive heat shrink tubing thickening method (lowest cost, suitable for on-site rework)
Material: Double-walled adhesive heat shrink tubing with a 3:1 shrinkage ratio (6mm inner diameter, 1.5mm after shrinkage).
step:
Insert heat shrink tubing about 30mm long onto the wire (it must completely cover the bushing area).
Heat the adhesive layer evenly to 165°C using a hot air gun until it melts and fills the gaps in the wires.
After cooling, measure the outer diameter; it should be 3.5-4.5 mm.
Install the standard PG7 or PG9 connector in the normal manner.
Key parameters: The optimal outer diameter is 0.5-1mm smaller than the inner diameter of the bushing; if it is too thick, it will damage the insulation.
limitation:Not applicable to wire harnesses with pre-installed connectors (cannot be fitted).
Option 1B: Replaceable multi-aperture bushing (recommended for mass production)
principle: Some brands of connectors (such as Heyco and Lapp) offer replaceable rubber cores with hole diameters of 1.5mm, 2mm, 3mm, etc.
operate: Purchase bushing cores that match the outer diameter of the conductor directly to replace the original universal cores.
Notice: Different brands have different thread specifications, so it is recommended to stick with one supplier.
Option 1C: Silicone injection-assisted method (temporary remedy)
step:
Tighten the standard connector but leave half a turn.
Inject RTV silicone (such as Dow Corning 734) into the gap between the bushing and the wire using a syringe.
Tighten the connector completely and squeeze out any excess silicone.
Allow to stand and cure for 24 hours.
shortcoming: It is not removable; the seal must be broken for repair.
Factory experience: For projects with an annual usage of more than 1,000 sets, we recommend directly customizing molds to produce multi-aperture bushings, which can reduce the cost per unit to below $0.2.
Core tools: Multi-hole insert (or split bung). This is a rubber or silicone block with multiple pre-drilled holes, each wire is individually sealed.
Three ways to obtain multi-hole inserts:
Installation steps (taking a pre-made multi-hole plug as an example):
Preprocessing: Arrange all wires, trim them neatly, and strip off the outer sheath (if there is a shielding layer, it needs to be removed).
Threading: Each wire should be threaded through a single hole on the connector. Note: Do not pull on the wire; a small amount of silicone grease can be applied for lubrication.
position: Adjust the plug position so that the exposed wire length is consistent (about 15-20mm for subsequent soldering).
Press in: Push the plug into the connector body, ensuring it is fully in place (there is usually a step limit).
Tighten: Tighten the connector nut. Torque reference value: 1.5-2 N·m for nylon connectors (add 1/4 turn after hand tightening).
Key data: Insert hole diameter = wire outer diameter + 0.2~0.3mm.
Too tight: Damage to the wire insulation leads to decreased insulation over long-term use.
Too loose: Insufficient compression, resulting in seal failure.
Emergency alternatives when no plug-in is available (non-vibration environment only):
Multiple wires are arranged side by side, and the entire bundle is wrapped with wide heat shrink tubing (with adhesive) to form a single "elliptical cable" with an outer diameter controlled at 4-5mm. Then, it is treated using the single-wire thickening method. This method cannot guarantee that the gaps between each wire are completely sealed and is only suitable for scenarios with IP65 ratings or lower.
Many engineers worry that adding openings will lower the enclosure's protection rating. However, by following the procedures below, it is entirely possible to add new entry points while maintaining an IP68 rating.
Recommended tool: Step drill bit
advantage: Self-centering, progressive hole enlargement, high hole roundness, and few burrs.
Not recommended: Ordinary twist drill (prone to deviation, producing a lot of burrs).
Standard operating procedure (taking aluminum alloy casing as an example):
mark: Use a center punch at the opening location, at least 1.5 times the wall thickness away from the edge of the casing (to avoid stress concentration).
Guide hole: Drill through with a 3mm twist drill (for positioning step drills).
Hole enlargement: Gradually increase the feed depth to the target diameter using a stepped drill bit. Key: Each feed depth should not exceed one step, and retract the drill bit to remove chips.
Chamfering and deburring: Using a 60° or 90° chamfering tool, gently rotate to remove burrs from both the inner and outer walls. Inspection method: It should feel smooth to the touch without any stinging sensation.
clean: Wipe around the hole with alcohol to remove oil and aluminum shavings.
Special considerations for plastic casings:
Use a sharp drill bit and drill at a low speed (<500 RPM) to avoid heat melting.
After drilling, the edges can be manually smoothed by rolling fine sandpaper into a cone shape.
Do not use a chamfer (it will scratch the surface); instead, gently scrape off any burrs with a utility knife.
Structural strength verification:
After opening the hole, the tensile strength of the area decreases by approximately 15-25%, but this is perfectly adequate for static sealing applications. If the housing needs to withstand higher internal pressures (such as deep water), it is recommended to increase the wall thickness (with local reinforcement) or use a metal insert injection molding process.
Factory services: We can provide custom housings with pre-drilled holes (threaded holes, plain holes), all of which are chamfered, eliminating the uncertainty of on-site machining. Please provide your drilling drawings.
Many of our clients are startups or in the R&D/prototype phase, with limited budgets but unwilling to resort to cheap, unreliable hot melt adhesives. The following solutions are ones that have been tested and proven effective."Middle Route"Cost is controlled at $2-6 per inlet, protection capability reaches IP66~IP67, while retaining the possibility of later upgrade to standard connectors.
The core idea behind this combination is to use 3D printing to solve the problem of "non-standard wire shapes not matching standard connectors" and to use marine-grade sealant to ensure long-term weather resistance.
Applicable scenario determination (meeting all three of the following criteria simultaneously)
Number of wires: 1-6 pieces, diameter 0.5mm~2.5mm (22-30 AWG)
Environmental requirements: Exposed to rain, or occasional short-term immersion in water (<0.5 meters, <30 minutes).
Yield: Production volume <500 sets/year, not suitable for mold making.
Materials list (including reference prices, in US dollars)
Factory notice: Do not use PLA or ABS printed with ordinary FDM for bushings—they are too stiff to be compressed and deformed, and they lack elasticity. TPU is the only recommended material.
Design/Obtain Bushing Model
If you have your own 3D printer, download or design a cylinder with an outer diameter 0.5mm smaller than the inner diameter of the connector body (for example, if the inner diameter of the connector is 8mm, then the outer diameter of the bushing should be 7.5mm).
Number of inner holes = number of wires, and diameter of each hole = outer diameter of wire + 0.2mm.
Recommended CAD parameters: Length 15mm, chamfered ends R0.5mm
No printer? You can find printing services on Taobao or Fiverr, with a single print job costing approximately $1-2.
Conductor pretreatment
Strip 5mm of the outer sheath from all wire ends and tin-dip or crimp terminals (to prevent splitting).
Wipe the outer sheath of the wire with alcohol to remove oil stains.
Threading and positioning
Each wire is passed through its corresponding inner hole independently.
Adjust the bushing position so that it is located in the middle of the wire harness (it should eventually be completely enclosed inside the connector).
Apply sealant (key step)
Apply a uniform layer of 3M 5200, approximately 1 mm thick, to both ends and the outer circumference of the bushing.
Notice: Do not clog the inner hole; apply the adhesive only to the solid area.
Assembly connector
Push the "wire + bushing" assembly into the connector body until it reaches the bottom.
Tighten the connector nut by hand first, then use a wrench to add 1/4 turn (excessive force will squeeze out all the adhesive, making it ineffective).
Curing and Inspection
Allow to cure for 48 hours (3M 5200 requires 7 days to fully cure, but low-pressure testing can be performed after 48 hours).
Do not move or vibrate during curing.
A simple airtightness test can be performed using the immersion method (see Part VI).
measured data
Our lab tested five samples:
wire: 3 26 AWG silicone wires
Water depth: 0.5 meters
time: 24 hours
result: No visible water seepage was observed in any of the five samples (the inner walls were dry).
Inspection after violent destruction: The sealant completely filled all the tiny gaps.
Limitations disclosure (very important)
This solution cannot replace an IP68-certified industrial-grade solution. It is suitable for:
Prototype during the research and development phase
Internal tools, outdoor display equipment
Projects with a very low budget but requiring a certain level of waterproofing
If your product requires CE, FCC, UL, or IP rating certifications, please skip this option and use a pre-made multi-port connector directly.
This section is based on real failure data from our factory's after-sales analysis. Below are six of the most frequently occurring pitfalls, along with corresponding preventative measures and on-site inspection methods.
Phenomenon: The system was well-sealed during installation, but water leakage occurred after three months. Upon disassembly, it was found that the bushing had hardened, cracked, or undergone permanent compression deformation.
root cause:
Ordinary nitrile rubber (NBR) is not resistant to ultraviolet light and ages after 3-6 months of outdoor use.
If the difference between the bushing bore diameter and the wire outer diameter is too large (>1mm), the bushing will lose its elasticity after long-term compression.
Preventive measures:
Outdoor applications mandate the use of EPDM or fluororubber (Viton) connectors, increasing costs by approximately 30%, but extending lifespan by 5 times.
Bushing bore selection: wire outer diameter + 0.5mm (interference fit)
At the time of each batch of goods received, the inner diameter of the bushing is checked by calipers.
On-site inspection: Press the bushing with your finger; it should feel soft and spring back quickly. If it feels hard or cracked, replace it immediately.
Phenomenon: After tightening the connector, there was slight water leakage at the O-ring. Upon removing the connector, a small cut was found on the O-ring.
root cause: The O-ring was not chamfered after being drilled by hand, and the burrs cut the O-ring like knives.
Preventive measures:
Mandatory requirement: Each opening must be chamfered (use a chamfering tool for metal casings, and use fine sandpaper rolled in a conical shape for plastic casings).
After chamfering, rotate your finger around the inside of the hole once – there should be no stinging sensation.
For mass production, consider using stamping or precision drilling processes.
On-site repair: Carefully remove the burrs with a micro file or deburr, replace the O-ring, and reassemble.
Phenomenon: A small amount of water was found inside the casing, but all external seals appeared to be intact. Upon inspection of the wiring, minor cuts were found in the sheath.
root cause: During the stripping or threading process, the metal shielding layer or conductor may puncture the inner wall of the sheath. Water can then enter the outer casing through the damaged area, flowing into the casing via capillary action between the multiple copper wires.
Preventive measures:
Use specialized wire strippers when stripping wire to avoid the blade cutting too deep.
For multi-strand wires, immediately after stripping, tin-dip or crimp terminals to seal the gaps between the wire cores.
Before the wire enters the sealed area, a section of adhesive heat shrink tubing (approximately 20mm in length) is fitted over it. After heating, the adhesive layer will seal the end of the sheath.
Repair of damage: Apply a ring of RTV silicone to the damaged area, then cover it with heat shrink tubing and allow it to cure.
Phenomenon: After the equipment has been running for a period of time in a vibrating environment such as vehicles and water pumps, the seal fails and the joint nut can be turned directly by hand.
root cause: Under continuous vibration, the self-locking performance of the threaded joint of the nylon connector is insufficient to maintain the torque.
Preventive measures (in recommended order):
Use a nylon lock nut: tighten another lock nut on the outside of the joint, and lock it in place.
Apply threadlocking adhesive: medium strength (such as Loctite 243), apply to the threads on the outside of the housing, and then tighten the nut.
Choose metal connectors: Brass or stainless steel connectors with spring washers offer better vibration resistance than nylon.
Notice: If the conductors are subject to tensile forces, additional stress relief measures must be implemented (e.g., adding cable tie points to the casing).
Phenomenon: After being exposed to the outdoors for a period of time (weeks to months), the exterior developed noticeable condensation and even water accumulation inside. The external seals remained intact.
root cause: The temperature difference between day and night in the sealed outer shell causes changes in internal air pressure—during the day, the air expands due to heat, forcing some air out from weak points in the seal; at night, the air cools and contracts, drawing in humid air from the outside. Moisture condenses and accumulates on the inner wall.
Preventive measures:
Install a miniature waterproof and breathable valve (made of EPTFE membrane, allowing gas exchange but blocking liquid water and dust) on the outer casing. The cost is approximately $1-2 per valve, completely solving this problem.
If there is no vent valve, a desiccant pack can be placed inside the casing (which needs to be replaced regularly), but this is only a temporary solution.
Factory Recommendation: For equipment used outdoors for extended periods, a vent valve is standard equipment; do not rely on sealed joints to withstand the elements.
Phenomenon: When ordinary silicone sealant is used to seal gaps, the sealant layer cracks and peels off after two months, completely losing its sealing ability.
root cause: Ordinary silicone sealant (acetic acid type) is not resistant to ultraviolet light and has poor adhesion to most plastic casings.
Preventive measures:
Use only annotations"Weather-resistant", "UV-resistant"RTV silicone (such as Dow Corning 734, GE SCS1200).
Alternatively, polyurethane sealants (such as 3M 5200 or SikaFlex) can be used, whose bonding strength and weather resistance are far superior to ordinary silicone sealants.
Absolutely avoid: Hot melt adhesive (EVA-based) and acrylic adhesive (commonly known as "AB glue") are used for outdoor waterproofing.
Simple identification: Squeeze a small amount of adhesive onto a transparent plastic sheet and place it outdoors in direct sunlight for a week. If it does not powder, change color, and has good adhesion, it is considered qualified.
Before mass production, it is recommended to perform at least one airtightness verification on each new design. The following is a commonly used low-pressure immersion method in factories:
Required tools
A transparent bucket (at least 0.5 meters deep)
Compressed air source (a bicycle pump will suffice).
A sealing plug with a valve stem (or a modified scrapped connector).
Dishwashing liquid (for leak detection)
Operating steps
Seal off all other openings: Install and tighten all wire connections, vent valves, etc., according to the actual plan.
Inlet pressurization port: Make a pre-drilled threaded hole (e.g., 1/8" NPT) in the housing to install a valve stem or quick coupler. If no pre-drilled hole is available, a wire can be replaced with a hollow tube and sealed with sealant.
Inflate: Slowly inflate with an air pump to 3-5 psi (approximately 0.2-0.35 bar).Notice:Do not exceed 50% of the casing's design pressure (for ordinary waterproof cases, it is recommended not to exceed 10 psi).
Flooding: Immerse the entire casing in water for 30 seconds. Observe whether any bubbles emerge.
Judgment:
No bubbles→ Basic sealing, IP67 compliant
tiny, scattered bubbles→ There is a minor leak; it needs to be repaired with adhesive or the seal needs to be replaced.
Continuous bubbles→ Major leak, rework required
Precision specification: This method can detect leaks at the 0.1mm level, which is sufficient to simulate IP67 test conditions. However, it cannot replace the precise testing conducted by a certified laboratory.
For equipment that operates outdoors for extended periods, it is recommended to establish a regular inspection system.
Every 6 months
Check all connector nuts for looseness (tighten them by hand; resistance indicates normal operation).
Inspect rubber parts (bushings, O-rings) for visible cracks, hardening, or deformation.
Open the casing (if permitted) and inspect the interior for condensation, rust, or white powder (salt spray residue).
Wipe the inside of the wire inlet with a dry paper towel to check for moisture.
each year
For detachable connectors, replace the O-rings and bushings (as a preventative maintenance).
For non-permanently sealed interfaces, reapply a layer of RTV silicone (after surface cleaning).
Test the air permeability of the vent valve (blow gently with your mouth; you should feel resistance but be able to let air through).
Triggered checks (check immediately if any of the following conditions are met)
The equipment suddenly malfunctions (sensor reading drift, short circuit alarm).
Visible cracks or discoloration on the exterior of the casing
The equipment has been subjected to accidental impact or drop.
The table below summarizes recommended solutions for different wire configurations and usage scenarios, which can be directly used for BOM selection.
Table 2: Comparison of Conductor Specifications and Recommended Solutions
Table 3: Comparison of Thread and Hole Sizes for Commonly Used Cable Connectors
Notice: NPT threads are tapered pipe threads, which are prone to cracking when tapped on plastic casings, so their use is not recommended. Metric (M) and PG threads are safer choices.
postscript: All solutions, data, and parameters in this article are derived from our laboratory tests and customer feedback. Due to differences in materials, environments, and usage methods, we recommend conducting your own verification before large-scale application. If you require technical support for specific products, please contact our engineering team for selection advice.
){kind=link}
){kind=link}
){kind=link}
){kind=link}