Split Grounding Bushing with Removable Spacer for Conduit
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Solution Overview
Problem
The variation in outer diameters of electrical metallic tubing (EMT) and rigid conduit of the same trade size, particularly for sizes two inches or less, poses a challenge in using a single split grounding bushing that can accommodate both, necessitating a solution for secure electrical bonding and grounding in solar panel installations.
Innovation Solution
A split grounding bushing design featuring a first and second metal bushing portion with a hinge, grounding screws, a removable metallic spacer, and insulator portions, allowing for adjustable fitment on EMT and rigid conduit, with a removable spacer having a cylindrical shape and post for secure electrical bonding and easy installation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single split grounding bushing design is used for both EMT and rigid conduit, then device complexity is reduced, but adaptability to different outer diameters deteriorates due to significant OD variations between EMT and rigid conduit of the same trade size
Solution Approach 1:
The bushing is divided into two separate bushing portions that can be positioned on opposite sides of the conduit, allowing each portion to independently accommodate different outer diameters. This segmentation enables the grounding bushing to adapt to both EMT and rigid conduit without requiring completely different designs.
Solution Approach 2:
A removable spacer is nested within one of the bushing portions to adjust for outer diameter variations. The spacer can be inserted or removed depending on whether the application requires EMT or rigid conduit compatibility, allowing a single bushing design to serve multiple conduit types.
2Adaptability or versatility
If the bushing is made adjustable to accommodate OD variations, then adaptability improves, but device complexity increases due to additional components like removable spacers
Solution Approach 1:
The spacer is designed as a removable component that can be taken out when not needed. This extraction approach allows the bushing to maintain simplicity for standard applications while providing adaptability when conduit outer diameter variations require accommodation.
Solution Approach 2:
The single bushing design is made universal by incorporating the removable spacer, allowing it to function with both EMT and rigid conduit. The same bushing structure serves multiple purposes depending on whether the spacer is installed or removed.
3Reliability
If grounding screws are used to secure the bushing, then electrical bonding reliability improves, but ease of installation deteriorates due to threading requirements on thin-walled EMT
Solution Approach 1:
The bushing portions are designed to be dynamically positionable on opposite sides of the conduit, allowing installers to select optimal locations for grounding screw installation. This dynamic positioning enables avoidance of thin-walled sections in EMT while maintaining reliable electrical bonding.
Data Source
AI summary
A split grounding bushing for placement on an end of an EMT or a rigid conduit has first and second metal bushing portions forming a ring, a grounding screw extending through the first or second metal bushing portion to make electrical contact with the EMT or rigid conduit, a lug secured to one of the bushing portions, the lug configured to secure a ground conductor thereto, a hinge formed at a second end of the first and second metal bushing portions, so that the first and second bushing portions can be opened or closed, and a removable metallic spacer having a shape that is a section of a cylinder and having an inner smooth surface corresponding to an outer surface of the EMT, the removable spacer also having an outer smooth surface corresponding to an inner surface of the second bushing portion.