Electrical Box Connectors, Electrical Conduit Fittings and Knockout Seals

Electrical box connectors and fittings hold cable or conduit at a box, protect wires at sharp edges and close unused openings. Getting the fitting right gives you a secure connection without leaving cable sheathing or wire insulation against bare metal. Buy for the job at that opening: holding cable, connecting conduit and closing a knockout each take their own part.

Knockout seals for unused box openings

Knockout seals close openings left unused in an electrical box. Buy the seal that matches the knockout size you’re closing. A cable connector belongs where cable enters; a knockout seal finishes the opening where nothing passes through.

The Halex 1/2-inch steel knockout seals come in a four-pack. That’s the buy for closing several unused 1/2-inch knockouts during a renovation. Choose the 3/4-inch steel knockout seal for a 3/4-inch knockout; the larger size answers a different opening, not a heavier-duty job.

Fitting	Named size	Material
Halex knockout seals, four-pack	1/2 inch	Steel
Knockout seal	3/4 inch	Steel

During Montana’s winter interior renovation season, include the unused openings when you go through the boxes affected by the work. Cable entries need connectors, and unused knockouts need seals. Make both part of the purchase so the box gets finished in the same job.

Electrical fittings: match the part to the connection

Electrical fittings secure cable or conduit, join raceways, protect conductors and close openings. For electrical junction box connectors, start with what enters the box. That choice comes before the fastening style.

For NM cable entering a metal junction box, buy an NM cable clamp connector. Its job is to hold the cable. That’s the right purchase for the cable entry because sharp knockout edges can cut sheathing and conductor insulation. A conduit-end bushing protects wires from a sharp conduit edge; choose it for that protection point, and choose the cable clamp for cable retention.

For armored cable, choose an armored-cable connector matched to the cable you’re using. Keep armored cable and flexible conduit distinct when choosing the fitting.

The main types of electrical conduit fittings have different jobs:

• A conduit connector attaches conduit to a box, enclosure or panel. A coupling joins conduit sections.
• EMT electrical conduit fittings match electrical metallic tubing. Compression and set-screw designs are unthreaded fitting types; choose the connection style and location suitability together.
• Flexible electrical conduit fittings attach flexible conduit to electrical boxes and devices. Liquidtight conduit uses gasketed fittings for sealed connections.
• PVC fittings for electrical conduit use solvent-cement or threaded adapters. Buy the adapter for the PVC connection you’re making.

For quick connect electrical fittings, snap-in attachment is a fastening choice. Match the connector to the cable or conduit before choosing how it attaches to the box.

For electrical LB fittings, the buying question is conductor access along the conduit run. Conduit bodies provide access to conductors in a completed raceway, while a pull elbow provides access at a direction change. Keep that access job separate from choosing the connector that terminates conduit at the box.

For adjacent boxes, buy a 1/2-inch zinc electrical box spacer to provide the connecting raceway, checking the knockout alignment so the straight connection lets both boxes sit properly against their mounting surface.

Choose for moisture and temperature changes

For a wet location, buy a fitting specifically listed for wet use. Concrete-tight means a separate qualification: it does not establish raintight or watertight suitability. Raintight does not mean waterproof, either. The wet-location listing is what makes the fitting the right buy for that exposure.

That distinction matters around Montana shops and pole barns, where a run can leave a heated room and enter a cold area. Warm-to-cool transitions and widely varying temperatures can cause condensation inside conduit. Great Falls chinooks bring the rapid temperature changes that make this worth accounting for when planning the run. Where conduit crosses areas with significantly different temperatures, expansion fittings reduce stress on the raceway and its supports.

The Pick

Buy the Halex 1/2-inch steel knockout seal four-pack for several unused 1/2-inch openings, and the 3/4-inch steel seal for a 3/4-inch opening. Buy an NM cable clamp connector to hold NM cable entering a metal box, or a matching armored-cable connector for armored cable. Choose the 1/2-inch zinc electrical box spacer for the connecting raceway between adjacent boxes with aligned openings.

Frequently Asked Questions

What fittings do you use with EMT conduit?

EMT conduit uses fittings made for electrical metallic tubing, including compression and set-screw types. For a run encased in concrete, choose fittings marked concrete-tight and follow any taping condition on the package. Some set-screw fittings need that tape to qualify, and concrete-tight doesn’t establish wet-location suitability.

What are electrical fittings used for?

Electrical fittings secure cable or conduit, join raceways, protect conductors at entries and close unused knockouts. Choose the part for the job at that connection: a cable clamp holds cable, while a conduit-end bushing protects wires from sharp edges. If a fitting has a throat liner, leave it in place because some designs rely on that liner to protect conductor insulation.

What fittings do you need for flexible electrical conduit?

Flexible conduit connectors come in straight and angled designs, so the direction of the box entry helps you choose the shape. Liquidtight conduit uses gasketed fittings to seal the connection. Match the fitting to the conduit type before choosing the shape; the gasket is part of the sealing arrangement.

What are electrical LB fittings used for?

An LB conduit body gives you access to conductors at a change in the conduit run’s direction, which helps when pulling wire. Position it where you can reach the cover after the surrounding work is finished. That access remains useful after the raceway is complete.