Metal electrical conduit connector fitting with threaded body and locknut

Electrical Conduit Fittings & Connectors: EMT Sizing and Which Connector to Use

Conduit fitting mistakes are rarely about the wrong part - they're about the wrong connector type for the environment, or a run that's overfilled or unsupported. Here's how to match conduit, connector, and hardware to the actual job.

EMT, rigid, and PVC: three different conduit types, three different jobs

EMT (electrical metallic tubing) is thin-wall steel conduit - the most common choice for exposed indoor wiring in commercial and residential work. It's not threaded; connections are made with set-screw or compression fittings that clamp onto the tube. Rigid metal conduit (and IMC) has a heavier wall and can be threaded, used anywhere the run needs more physical protection - exterior runs, areas exposed to impact. PVC conduit is nonmetallic, solvent-welded like PVC pipe, and the standard choice underground or in wet, corrosive locations where metal conduit would need extra protection.

Set-screw vs. compression vs. liquid-tight: match the connector to the environment

Set-screw connectors are the simplest and most common choice for EMT in dry, indoor locations - a screw bites into the tube to hold it in the connector. Compression connectors thread a ring down over the conduit for a tighter, more environmentally sealed connection, and are the better choice in damp locations or anywhere vibration could work a set screw loose over time. Squeeze connectors are built specifically for AC, MC, or flexible metal conduit rather than rigid EMT. Liquid-tight connectors are for flexible liquid-tight conduit in wet or oily environments - equipment rooms, outdoor equipment connections - where a standard connector isn't rated for the exposure.

Locknuts and reducing washers: securing the connection at the box

A locknut threads onto a connector or conduit body from inside the box or enclosure to hold it in place - sized to match the conduit's trade size (1/2 in., 3/4 in., 1 in., and up). If the knockout in the box is larger than the connector, a reducing washer steps the connection down to fit properly rather than leaving it loose in an oversized hole.

Support intervals and fill capacity aren't optional

Conduit needs to be supported at regular intervals along a run and within a set distance of boxes and fittings - an unsupported run sags, stresses the connectors, and can pull loose over time. Conduit hangers are sized by number to match conduit trade size, the same fill-capacity logic that applies to electrical boxes also applies to conduit itself: don't run more conductors through a given trade size than its fill rating allows, even if they physically fit.

Buying to match your actual usage

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Quick buying checklist

  • Match conduit type (EMT, rigid, PVC) to the environment and physical protection the run needs
  • Use set-screw connectors for dry indoor EMT, compression or liquid-tight for damp/wet or vibration-prone locations
  • Size locknuts to the conduit trade size, and use reducing washers on oversized knockouts
  • Support conduit at regular intervals and within code distance of every box or fitting
  • Don't exceed the conduit's fill rating for the number of conductors it carries
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