Threadless Grounding Bushing with Removable Spacer for EMT and Rigid Conduit
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Solution Overview
Problem
The variation in outer diameters between electrical metallic tubing (EMT) and rigid conduit of the same trade size poses a challenge in providing a grounding bushing that can accommodate both, ensuring proper grounding as required by electrical codes, especially in solar panel installations.
Innovation Solution
A threadless grounding bushing with a cylindrical metal body, featuring a smooth inner surface for EMT and a central bore for conductors, along with a removable spacer and insulating ring, allows secure contact with both EMT and rigid conduit, accommodating size variations through adjustable components like a post and slot for easy installation and removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a grounding bushing is designed to fit rigid conduit with larger outer diameter, then it cannot properly contact EMT with smaller outer diameter, but if designed to fit EMT, then it cannot properly contact rigid conduit
Solution Approach 1:
The grounding bushing is divided into multiple functional segments: a first portion with an inner smooth cylindrical surface for rigid conduit contact, and a second portion with threaded holes for EMT contact. This segmentation allows each portion to be optimized for its specific conduit type while working together as a unified grounding solution.
Solution Approach 2:
The grounding bushing is designed to perform multiple functions by accommodating both rigid conduit and EMT through its dual-portion structure. The bushing can be selectively installed on different conduit types, making a single product universally applicable to both conduit systems despite their dimensional differences.
2Ease of operation
If threaded holes are provided for EMT contact, then mechanical contact is achieved, but the bushing cannot properly accommodate rigid conduit with larger outer diameter
Solution Approach 1:
The bushing body is segmented into a first portion optimized for rigid conduit (smooth inner surface) and a second portion optimized for EMT (threaded holes). This allows the same bushing structure to provide proper contact mechanisms for both conduit types without compromise.
Solution Approach 2:
Different regions of the bushing have different surface qualities: the first portion has a smooth cylindrical surface for rigid conduit contact, while the second portion has threaded holes for EMT contact. This local differentiation of properties allows each region to interact optimally with its corresponding conduit type.
3Reliability
If the inner smooth cylindrical surface is designed for rigid conduit, then rigid conduit contact is achieved, but EMT with smaller outer diameter cannot be properly accommodated
Solution Approach 1:
The contact surface is segmented into two distinct portions: an inner smooth cylindrical surface for rigid conduit and an outer surface with threaded holes for EMT. This segmentation enables reliable contact with both conduit types through appropriately designed contact interfaces.
Solution Approach 2:
The grounding bushing achieves universality by incorporating two different contact mechanisms in one structure, allowing it to reliably ground both rigid conduit and EMT systems despite their different outer diameters and surface characteristics.
Data Source
AI summary
A threadless grounding bushing for placement on an end of an EMT or rigid electrical conduit has a bushing body with a first portion with an inner smooth cylindrical surface dimensioned for receipt of a rigid conduit; a second portion with a central bore for the passage of conductors therethrough, the second portion dimensioned to form a stop relative to a terminating end of a rigid conduit or EMT received in the first portion; at least one set screw that extends through the first portion to make contact with the EMT or rigid conduit; a lug secured to the bushing body having an opening to secure a ground conductor thereto; and a removable spacer with an inner surface corresponding to the outer surface of an EMT and having an outer surface corresponding to the inner smooth cylindrical surface of the first portion of the bushing body.