Conduit & Grounding Bushings

How to Choose Conduit Bushings and Grounding Fittings

Conduit bushings protect wiring at raceway terminations, provide connections for required bonding arrangements, or adapt compatible threaded openings to different trade sizes. Each function requires a different fitting. A standard zinc bushing may provide a smooth conductor entry, but it cannot replace a grounding bushing where a bonding jumper is required. Similarly, a reducing bushing changes the connection size without replacing the need for suitable conductor protection. Start with the raceway type, fitting function, and electrical installation requirements before comparing materials and sizes.

Quick Conduit Bushing Selection Guide

• Threaded rigid conduit entering a panel: Check a standard or insulated-throat bushing that meets conductor-protection requirements.
• Service raceway requiring additional bonding: Select a suitable grounding bushing and properly specified bonding jumper.
• Large threaded hub with smaller conduit: Match a reducing bushing to both trade sizes.
• Armored cable termination: Verify whether a compatible anti-short bushing is required.
• Replacement fitting: Confirm trade size, attachment method, material, and product listing.

Insulated vs. Non-Insulated Conduit Bushings: Protect Conductor Insulation

Insulated and non-insulated conduit bushings both address conductor protection at raceway ends, but their throat construction differs.

An insulated bushing has a smooth insulating surface intended to reduce the risk of abrasion where conductors pass through the fitting. A non-insulated metallic bushing relies on its formed metal throat to provide protection. Neither type should be selected without considering the conductor sizes and applicable installation requirements.

For example, the Orbit CB-100 1-inch zinc conduit bushing uses a non-insulated throat and is designed for compatible threaded Rigid/IMC conduit terminations.

Where raceways contain insulated circuit conductors 4 AWG or larger, NEC 300.4(G) establishes specific abrasion-protection requirements. The permitted methods include identified fittings with smoothly rounded insulating surfaces, certain listed metal fittings with smoothly rounded edges, and other specified protective arrangements.

Under the 2023 NEC wording, this protection must be provided before conductor installation. An insulating bushing is a common solution, but it is not the only permitted method.

Selection rule: Identify the conductor sizes and required protection method before choosing the bushing. A smooth-looking metal fitting should not be assumed to satisfy the applicable requirements without the proper identification or listing.

Grounding Bushings: When Is a Bonding Jumper Required?

Grounding bushings, often called bonding bushings, provide a connection point for a bonding conductor at an electrical raceway termination. They are not required on every metal conduit connection.

At service equipment, NEC 250.92 establishes specific bonding requirements. Standard locknuts and ordinary bushings cannot serve as the sole bonding method for service raceways. Where connections involve reducing washers or impaired concentric or eccentric knockouts, an appropriate bonding arrangement may require a jumper around the connection.

For example, consider a 2-1/2-inch metallic service raceway entering an enclosure through concentric knockouts. If the installation requires a bonding jumper at that entry, a suitable grounding bushing provides a connection point for the specified conductor.

Lumera carries products such as the Morris 14579 insulated-throat grounding bushing, which combines a protective throat with an aluminum bonding lug.

Before selecting a grounding bushing, verify:

• Conduit size: Match the bushing to the permitted raceway connection.
• Bonding conductor: Confirm the required wire size and material.
• Lug capacity: Check the approved conductor range and number of conductors.
• Connection method: Follow the manufacturer's attachment and torque requirements.
• Termination point: Connect the jumper to the approved bonding point for that electrical system.

For related equipment connections, review suitable electrical grounding and bonding lugs.

Selection rule: Determine the bonding requirements from the electrical design and applicable NEC provisions before selecting a grounding bushing. The presence of a lug does not establish the correct jumper size or termination point.

Reducing Conduit Bushings: Match Both Threaded Trade Sizes

Reducing bushings adapt a larger compatible threaded opening to a smaller threaded conduit or fitting. Unlike standard protective bushings, their primary function is changing the connection size.

A reducing bushing marked 3 inches by 2 inches has a larger threaded connection that fits the specified 3-inch opening and a smaller threaded connection that accepts the compatible 2-inch component.

For example, the Morris 14681 steel reducing bushing is identified as a 3-inch by 2-inch reducer for compatible threaded Rigid/IMC applications.

Reducing bushings are available in different materials, including steel and malleable iron. Material selection should follow the specific fitting's mechanical requirements, environmental exposure, and project specifications rather than assuming one material is universally suitable.

A reducing bushing should not automatically be substituted for reducing washers at a box knockout. These components use different mounting arrangements and can have different bonding implications.

Selection rule: Record the larger and smaller trade sizes separately, then confirm threading, fitting compatibility, and any required bonding provisions.

Anti-Short Bushings for Armored and Metal-Clad Cable

Anti-short bushings protect conductor insulation where a metallic cable armor or sheath terminates. These small inserts are commonly associated with armored cable connections and are sometimes called redheads.

For example, the Orbit ASB-38 plastic anti-short bushing is identified for compatible 3/8-inch cable or flexible metal conduit applications.

Not every metallic cable termination has the same requirements. Type AC cable and Type MC cable are covered by different NEC articles and fitting requirements.

Type AC cable generally requires an anti-short bushing or equivalent protection under its applicable requirements. For Type MC cable, listed termination fittings are designed to protect the conductors, and an additional anti-short bushing is not universally required by NEC 330.40.

The fitting manufacturer's instructions, the cable listing, project specifications, and local requirements must still be followed.

Selection rule: Identify the exact cable and connector type before ordering anti-short bushings. Do not assume every armored or metal-clad cable termination needs the same insert.

Conduit Bushing Compatibility: Rigid, IMC, EMT, and Cable Connections

Conduit trade size is only one part of fitting compatibility. Rigid metal conduit, intermediate metal conduit, electrical metallic tubing, and flexible cable systems use different connection methods.

A threaded bushing designed for a 1-inch Rigid/IMC connection should not automatically be installed on unthreaded 1-inch EMT. The nominal sizes may match, but the attachment methods differ.

EMT installations generally use approved connectors that terminate the tubing at an enclosure. Some connectors incorporate an insulated throat, while other configurations may require additional conductor-protection hardware.

For these applications, compare compatible EMT connectors and couplings before specifying a separate bushing.

Conduit bushings also perform a different job from conduit bodies. An LB, LL, LR, C, or T conduit body provides accessible space along a raceway for routing or pulling conductors. A bushing protects or completes a termination; it does not create an intermediate pulling point.

Where conductor access is required along the run, review suitable conduit bodies and condulets.

Selection rule: Match the bushing to the actual raceway or connector design. A similar trade-size marking does not establish that two different connection systems are interchangeable.

Conduit Bushings for Outdoor and Industrial Electrical Installations

Conduit bushing material and product listings affect suitability for outdoor or industrial environments. Steel, die-cast zinc, malleable iron, and insulated metallic designs have different characteristics, but material alone does not establish an environmental rating.

For example, a bushing used inside a dry electrical room may not have the same exposure requirements as a fitting installed at an outdoor service enclosure.

Where a connection is exposed to moisture, corrosive conditions, or other environmental hazards, verify the suitability of the complete raceway and enclosure assembly.

A conduit bushing generally does not replace a raintight connector, sealing fitting, or required enclosure gasket. It also does not make an otherwise unsuitable box acceptable for a wet location.

For exterior raceway terminations, coordinate the selected fitting with appropriately rated weatherproof electrical boxes.

Where the installation requires a larger enclosure or an accessible pull point, review compatible junction boxes and enclosures.

Selection rule: Verify the fitting's listing and the complete installation environment before ordering. Never assume every metallic bushing provides the same level of corrosion or moisture protection.

Ordering Conduit and Grounding Bushings for Electrical Projects

For commercial electrical projects, organize bushings by raceway connection and installation function rather than ordering every fitting under one general description.

For a project with forty conduit terminations, separating protective bushings, grounding bushings, and reducers can prevent missing bonding hardware or ordering incorrect sizes.

Prepare a material list containing:

• Standard, insulated, grounding, reducing, or anti-short bushing type
• Conduit or cable system and trade size
• Both trade sizes for reducing fittings
• Insulated or non-insulated throat requirements
• Bonding conductor size and lug compatibility
• Material and environmental requirements
• Manufacturer part numbers and required quantities

For grounding-related installations, compare additional hardware in Lumera's grounding and bonding collection.

Eligible business buyers can review Lumera Electric's trade account options when planning recurring electrical purchases.

Request a Quote for Conduit and Grounding Bushings

For larger orders or projects requiring several bushing configurations, request a project quote from Lumera Electric.

Include the raceway schedule, trade sizes, manufacturer part numbers, quantities, and any required bonding or environmental specifications. Electrical bonding connections should be specified and installed by qualified personnel following the manufacturer's instructions and locally adopted electrical code.

Conduit & Grounding Bushings FAQs

What is the difference between a grounding bushing and an insulated conduit bushing?

A grounding bushing provides a connection point for a bonding conductor, while an insulated conduit bushing primarily protects conductor insulation at the raceway entry. Some grounding bushings include an insulated throat and perform both functions. A plain insulated bushing does not automatically provide a bonding connection. Select according to the protection and bonding requirements of the installation.

Does every metal conduit require a grounding bushing?

No. Grounding bushings are required only where the electrical installation needs that type of bonding connection or an equivalent approved method. Ordinary metallic raceway connections may provide acceptable continuity when properly installed. Service equipment, certain higher-voltage circuits, and impaired knockout connections can have additional requirements under NEC 250.92 and 250.97. The correct method depends on the circuit and installation.

Are insulated conduit bushings required for 4 AWG and larger conductors?

NEC 300.4(G) requires specified protection against abrasion where raceways containing insulated circuit conductors 4 AWG or larger enter an enclosure or another raceway. An insulating bushing is one common solution, but certain listed metal fittings and other identified protective methods may also comply. Under the 2023 NEC, protection must be installed before the conductors.

What does a 3-inch by 2-inch reducing bushing mean?

A 3-inch by 2-inch reducing bushing adapts a compatible 3-inch threaded opening to accept a 2-inch threaded conduit or fitting. The larger size identifies the receiving opening, while the smaller size identifies the reduced connection. Both dimensions must match the installation. Verify the threading and approved application rather than ordering from either size alone.

Do MC cables require anti-short bushings?

Not universally. Listed Type MC cable fittings are required to provide suitable conductor protection, and NEC 330.40 does not generally require a separate anti-short bushing with every listed MC connector. Type AC cable follows different requirements. Always check the cable manufacturer's installation instructions, the fitting listing, and any local requirements before deciding whether an additional insert is needed.

What is the difference between a grounding bushing and a ground clamp?

A grounding bushing provides a bonding connection at a conduit or raceway termination. A ground clamp connects a compatible grounding or bonding conductor to an approved electrode or another specified connection surface, such as suitable pipe or structural material. Their functions and installation requirements differ. For electrode-related connections, review appropriate ground clamps rather than substituting a raceway bushing.