Underground electrical and cable systems are critical for the reliable delivery of energy to communities and industry, yet they operate in some of the world’s harshest environments. Link boxes that connect cable sheaths — either with or without sheath voltage limiters — to ground, along with enclosures that house sensors and monitoring systems, are integral parts of these systems.
These components are exposed to moisture, flooding, condensation, and extreme pressure and temperature fluctuations. Such conditions significantly increase the risk of corrosion, insulation degradation and failure of critical sheath bonding and grounding components.
To help mitigate these risks, manufacturers of link boxes and enclosures must demonstrate that their products meet verified watertight performance requirements.
As the central interconnection points for sheath crossbonding, solid bonding, single-point bonding and grounding systems, link boxes represent a critical interface where water ingress can directly compromise electrical continuity and the performance of protective components. They also represent a critical interface where water ingress can directly compromise electrical continuity and protective functions due to their common installation in manholes, handholes and at cable sheath bonding and grounding points. Moreover, link boxes installed in underground chambers may be periodically — or even permanently — submerged, further increasing the risk of moisture-related failures.
Consequences of water ingress
Water ingress into link boxes can accelerate corrosion of metallic parts, impair the operation of sheath voltage limiters, result in circulating currents, increase the risk of partial discharge and significantly shorten service life, ultimately reducing system reliability and personnel safety. Enclosures housing sensors and monitoring devices normally have very low tolerance for water intrusion, which would lead to monitoring device malfunctioning or severe damage. Watertightness testing helps determine whether enclosure design, gasket materials and cover interfaces can maintain complete water exclusion under realistic service conditions.
Climate-driven flooding and rising performance expectations
Rigorous water sealing verification and environmental testing have become essential to help reduce costly outages and extend asset life due to increasing climate-related flooding risks and rising performance expectations for transmission networks. At UL Solutions, we help support your efforts to meet and manage these challenges.
Beyond standards: real-world applications
While standards like IEC 60529 and NEMA 250 provide baseline protection levels against water ingress, today’s utility and infrastructure projects often require more. UL Solutions offers advanced water-submersion testing tailored to the needs of the high-voltage (HV) industry.
We offer water seal testing services in response to the new AEIC CS9-2024 requirements, which recommend enhanced protection against moisture ingress in link boxes. Water intrusion has been identified as a leading cause of corrosion, insulation degradation and failure of sheath bonding systems, compromising reliability and safety in underground transmission networks. By offering this service, UL Solutions helps manufacturers demonstrate compliance with industry specifications, improve system resilience and mitigate risks associated with environmental exposure.
We evaluate the sealing performance of:
- Link boxes and associated enclosures
- Sealed electrical enclosures and junction boxes
- Sensors and monitoring devices used within enclosures
- Cables, feedthroughs and tubing interfaces
Customizable testing for critical applications
We understand that no two projects are alike and offer custom test configurations to address specific performance requirements, including:
- Extended submersion durations
- Variable water pressure heights
- Thermal cycling and temperature control
- Project-specific environmental simulations (upon review)
Whether you are assessing a new product design or qualifying components for critical infrastructure, our experts review your field conditions and replicate the requirements in a controlled laboratory environment.
Third-party performance verification to support user qualification and procurement
The UL Marketing Claim Verification for watertight link boxes and enclosures provides independent, science-based confirmation of critical performance claims related to water exclusion.
Objective testing, auditing and inspection methods
By evaluating watertightness through objective testing, auditing and/or inspection, our service helps customers demonstrate enclosure performance beyond basic regulatory or self-declared claims, customized to each application or customer.
In addition, UL Marketing Claim Verification enhances market differentiation, simplifying utility and asset-declared claims and builds confidence among specifiers, inspectors and end users.
Differentiation from self-declared claims
Unlike safety certification, verification offers the flexibility to verify specific, customizable performance claims, allowing manufacturers and system integrators to highlight proven resistance to water ingress under realistic underground service conditions. The result is increased trust, reduced risk of disputed claims, and stronger support for procurement and long-term asset reliability decisions.
Service deliverables
Upon successful completion of watertightness verification, UL Solutions provides a comprehensive set of formal and market-ready deliverables, including:
- Test Report documenting the evaluation scope, test methods and verification basis
- Notice of Authorization and Certificate confirming claim verification
- UL Marketing Claim Verification Mark, approved for use on products, packaging and marketing materials
- Unique Verification Identifier, enabling public lookup of the verified claim on Verify.UL.com
- Searchable online listing of the verified watertightness claim for transparency and traceability
- Customer promotional enablement materials, supporting correct and consistent communication of the verified claim
These deliverables provide both technical documentation and marketing tools, enabling customers to confidently substantiate watertightness performance throughout the product life cycle.
Marketing Claim Verification service
UL Solutions Marketing Claim Verification for watertight link boxes and enclosures provides independent, science-based verification that critical sealing designs perform under real underground conditions. Through objective testing and assessment, we verify water exclusion performance for enclosures used in sheath cross bonding, single-point bonding and grounding systems where water ingress can directly compromise safety and reliability.
Build trust with utilities, inspectors and end users
Verified claims allow manufacturers and asset owners to confidently demonstrate durability, differentiate from self-declared claims and build trust with utilities, inspectors and end users through the UL Verified Mark.
Why UL Solutions?
With decades of experience across the utility and cable ecosystem, UL Solutions is a trusted partner to manufacturers, utilities and infrastructure developers. Our watertightness service is part of a broader medium-voltage (MV) and high-voltage (HV) portfolio, including:
- Certification and listing of MV cables and accessories
- Qualification testing for MV, HV, and extra high voltage (EHV) AC/DC land and submarine cables and accessories
- Field testing to support commissioning, diagnostics and asset management
- Advisory services for cable system reliability and failure resolution
Frequently asked questions
- What documentation do you need to scope a watertightness test?
Product drawings, sealing details, materials, intended installation, service environment and the specific watertightness claim or performance objective being evaluated are necessary.
- How do you determine passing or failing in a submersion test?
UL Solutions inspects for water ingress after exposure using visual checks, functional assessment or defined acceptance criteria tied to the performance claim.
- Can submersion be combined with thermal cycling to replicate seasonal or load-related temperature swings?
Yes. Submersion testing can be combined with thermal cycling to evaluate whether seals remain watertight as materials expand and contract with temperature changes. A comprehensive testing partner should be able to tailor temperature ranges, cycling sequences and submersion conditions to reflect seasonal climates or load-related heating while supporting claim-focused verification.
- Can UL Solutions witness in-field submersion or flooded vault conditions?
UL Solutions can witness submersion testing conducted outside the laboratory, including infield submersion or floodedvault conditions, when the environment, controls, and documentation support objective, repeatable results. Field witnessing may be appropriate for installations such as manholes, handholes, or underground chambers that reflect real-world service conditions.
Through our Field Engineering capabilities and the Witness Test Data Program (WTDP), UL Solutions can oversee testing performed at customer or third-party locations, provided the facilities, equipment, procedures, and personnel are technically equivalent to laboratory conditions.
- How are confidential results handled if a design does not pass on the first attempt?
Results are treated as confidential and shared only with the applicant, allowing design refinement before retesting or public claims.
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