PVC-MC Cable Fitting with Nested Grommets for Liquid-Tight Sealing
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Solution Overview
Problem
Existing electrical fittings fail to provide a liquid-tight and concrete-tight connection while ensuring proper grounding for PVC jacketed metal-clad (PVC-MC) electrical cables to electrical boxes or panels, especially in outdoor and concrete installations.
Innovation Solution
A liquid-tight and concrete-tight electrical fitting comprising a tubular body with a threaded end, an MC ring, a grommet, a bushing, a sealing ring, a locknut, and a gland nut, which creates a secure and watertight seal by compressing an elastomeric grommet around the cable, establishing a grounding path through conductive components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional electrical fitting is used to connect PVC-MC cable to an electrical box, then the cable can be mechanically secured, but the connection fails to provide both liquid-tight and concrete-tight sealing simultaneously
Solution Approach 1:
The patent employs nested sealing components where an inner grommet is positioned within an outer grommet, and a sealing ring is integrated within the fitting body. This nested arrangement allows multiple sealing functions (liquid-tight and concrete-tight) to be achieved within a single integrated fitting structure, resolving the contradiction between reliability and device complexity.
Solution Approach 2:
The fitting is divided into distinct functional segments: an inner grommet for liquid-tight sealing, an outer grommet for concrete-tight sealing, and a sealing ring for additional protection. Each segment performs a specific sealing function, allowing the complex requirement of dual-tight sealing to be achieved through modular, manageable components rather than a monolithic complex structure.
2Ease of manufacture
If the fitting structure is simplified to reduce complexity, then manufacturing becomes easier, but the ability to provide both liquid-tight and concrete-tight sealing is compromised
Solution Approach 1:
The fitting is designed as a universal component that simultaneously provides mechanical cable securing, liquid-tight sealing, and concrete-tight sealing functions. The multi-functional design integrates multiple sealing mechanisms into a single manufacturable part or assembly, achieving both ease of manufacture (through standardized production processes) and reliability (through comprehensive sealing capabilities).
3Adaptability or versatility
If the fitting is designed to accommodate a wide range of cable sizes, then versatility is improved, but the precision of the sealing connection may be compromised
Solution Approach 1:
The grommets are designed as elastomeric components that can dynamically adapt to different cable diameters through elastic deformation. When a cable is inserted, the grommet compresses and conforms to the specific cable size, maintaining precise sealing contact regardless of the cable diameter. This dynamic adaptability allows the fitting to accommodate a wide range of cable sizes while preserving sealing precision.
Solution Approach 2:
The sealing mechanism utilizes changes in the physical parameters of the elastomeric grommets, specifically their compressibility and elastic recovery. By leveraging these parameter changes, the fitting maintains consistent sealing pressure and precision across varying cable sizes, resolving the contradiction between versatility and manufacturing precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The fitting achieves a secure, watertight, and concrete-tight connection for a wide range of PVC-MC cable sizes, ensuring proper electrical grounding and accommodating outdoor and concrete installations, while maintaining electrical continuity between the cable, fitting, and electrical box.
Implementation Method 1
compressing an elastomeric grommet around the cable, establishing a grounding path through conductive components
Implementation Method 2
establishing a grounding path through conductive components, maintaining electrical continuity between the cable, fitting, and electrical box
Data Source
AI summary
A liquid-tight and concrete-tight electrical fitting for securing PVC jacketed metal clad (PVC-MC) electrical cable to an electrical box or panel. The electrical fitting includes a tubular fitting body having a threaded inbound and outbound end, an MC ring, a grommet, a bushing, a sealing ring, a locknut, and a gland nut. The grommet includes an inbound end with a conical outer surface and an outbound end with a flat abutment surface. A conical inner surface is provided on the bushing for engaging the conical outer surface of the grommet. The MC ring is a continuous ring including an inbound end, an outbound end, a ring portion, and one or more fingers extending from the ring portion. The fitting facilitates liquid-tight and concrete-tight connection and proper electrical grounding of PVC-MC cable to an electrical box or panel.