Electrical Metallic Tubing: Installation, Fill Limits, and Grounding

The installation rules for electrical metallic tubing come from NEC Article 358, which governs where EMT may be run, what trade sizes are permitted, how it must be supported and bent, how many conductors can share the raceway, and how it must be joined. The core requirements have stayed consistent across recent code cycles, so the rules below apply broadly regardless of which NEC edition your jurisdiction currently enforces.

Where EMT Can and Cannot Be Used

EMT is permitted for exposed and concealed wiring in most standard construction: inside walls, above ceilings, along commercial surfaces, and through framing in new residential work. In wet or damp locations, the fittings and connectors must be watertight. If the tubing will be buried in masonry or concrete, those fittings must be the concrete-tight type.¹

Galvanized steel EMT can be embedded in concrete or placed in direct contact with the earth with approved corrosion protection. Aluminum EMT needs supplementary corrosion protection in those same conditions. Recent NEC editions also permit direct burial of EMT when the fittings are specifically identified for that purpose, a change from older cycles that effectively barred it.

EMT is prohibited in the following situations:¹

Areas subject to severe physical damage, such as loading docks or vehicle zones where the thin wall could be crushed. Use rigid metal conduit or intermediate metal conduit there.
Environments where corrosion protection consists of enamel alone.
Cinder concrete or fill with permanent moisture, unless the tubing is shielded on all sides by at least two inches of non-cinder concrete or buried at least 18 inches below the fill.
Hazardous (classified) locations with flammable gases, vapors, or combustible dust, unless another NEC article specifically permits it for that classification.
As support for luminaires or other equipment. EMT is a raceway, not a structural member.

Inspectors who find EMT installed in a prohibited location will typically require removal and replacement with an approved wiring method. Depending on the jurisdiction, code violations can also carry fines and stop-work orders until the installation is corrected.

Permitted Trade Sizes

EMT is manufactured in trade sizes from ½ inch to 4 inches. The NEC does not permit anything smaller than ½ inch or larger than 4 inches.¹ Residential branch circuits usually run in ½-inch or ¾-inch EMT. Commercial and industrial work often calls for 1-inch through 2-inch tubing to accommodate larger conductor bundles or feeders. Sizes above 2 inches appear less often because they are harder to bend in the field.

Support and Securement

NEC 358.30 requires EMT to be fastened within three feet of every box, cabinet, conduit body, or other termination point. Between terminations, the tubing must be secured at least every 10 feet.¹ These are maximums. Runs through areas with vibration or movement should be strapped tighter.

Straps and hangers must be sized to the tubing diameter. A ¾-inch strap on ½-inch EMT lets the conduit rattle, and an undersized strap can crush the wall. Both compromise the continuous grounding path the raceway provides.

Exceptions to the Support Rule

When you fish an unbroken length of EMT (no couplings) through a completed wall or ceiling, the securement requirements do not apply.¹ The word “unbroken” matters. If a coupling is needed to make the run, the exception is lost. Horizontal runs through framing members at intervals no greater than 10 feet, with fastening within three feet of each termination, also satisfy the code.

Bends and Pull Points

The NEC limits total bends between pull points to 360 degrees, or the equivalent of four 90-degree bends. Exceeding that limit requires a pull box or conduit body to break the run into shorter segments.¹

Bends must not kink the tubing or reduce its internal diameter. A kinked bend creates a pinch point that damages wire insulation during pulling and may block conductors entirely. The NEC sets minimum bending radii by trade size. For ½-inch EMT with a standard one-shot bender, the minimum centerline radius is 4 inches. That radius grows with tubing size: 4½ inches for ¾-inch, 5¾ inches for 1-inch, on up to 16 inches for 4-inch EMT.

Conduit Fill Limits

NEC Chapter 9, Table 1 sets maximum fill percentages based on how many conductors share the raceway:

One conductor: 53% of the conduit’s internal area.
Two conductors: 31%.
Three or more conductors: 40%.

The two-conductor limit is lower because two wires tend to stack against each other and concentrate heat more than three wires distributed around the interior. These percentages prevent overheating and leave room to pull wire without stripping insulation. Chapter 9, Table 4 lists the exact square-inch areas for each trade size of EMT, and Table 5 lists the area of each conductor type and size. Comparing them tells you whether your planned wire count fits the conduit you selected.

Ampacity Derating

When more than three current-carrying conductors share a raceway, the heat they generate reduces the safe amperage each conductor can carry. The NEC requires derating the listed ampacity as follows:

4 to 6 conductors: 80% of rated ampacity.
7 to 9 conductors: 70%.
10 to 20 conductors: 50%.
21 to 30 conductors: 45%.
31 to 40 conductors: 40%.
41 or more: 35%.

Neutral conductors that carry only unbalanced current and equipment grounding conductors generally do not count toward these totals. You may have physical room in the conduit for the wires, and the ampacity math may still force you to upsize the conductors or split the run into two raceways.

Cutting, Reaming, and the No-Threading Rule

A hacksaw or a dedicated tubing cutter will size EMT to length. The tubing cutter leaves a cleaner cut with less burr. Either way, the NEC requires all cut ends to be reamed or otherwise smoothed to remove sharp edges inside the tubing.¹ Skip this step and the burr will slice through wire insulation the moment you pull conductors. A half-round file or the reamer blade on a conduit cutter handles it in seconds.

EMT cannot be threaded. Its thin wall does not have enough material to hold threads safely. Threaded connections require a different conduit type, such as rigid metal conduit or intermediate metal conduit. EMT connections are always made with set-screw or compression fittings.

Fittings and Connectors

Two main fitting styles join EMT and connect it to boxes. Set-screw fittings use small screws that bite into the outer wall of the tubing. They install quickly and work well in dry indoor locations. Compression fittings use a threaded nut that tightens an internal ring around the tubing, creating a more secure and weather-resistant connection. Wet locations and outdoor installations call for compression fittings rated raintight.

Every fitting must be made up tight per NEC 358.42. A loose connector breaks the electrical continuity of the raceway and compromises the grounding path.¹ Buried in masonry or concrete, all couplings and connectors must be the concrete-tight type. The right fitting installed loosely is just as bad as the wrong fitting.

Where a run crosses areas with significant temperature swings, such as a conduit passing from a heated interior through an exterior wall into an unconditioned space, NEC 300.7 requires expansion or deflection fittings to absorb thermal movement. Metal conduit expands and contracts with temperature, and without these fittings the raceway can buckle or pull apart at connections.

Pulling Conductors

Once the raceway is assembled, supported, and inspected, wires can be pulled. Push a fish tape from one box through the conduit to the next, attach the conductors at the far end, and draw the tape back through the smooth interior. For longer runs or runs with multiple bends, wire-pulling lubricant reduces friction between the conductors and the tubing walls. Confirm the lubricant is compatible with the conductor insulation; some wax-based products are not rated for certain jacket materials.

Verify the conductor count against the fill limits before pulling. Finding out you have too many wires for the conduit size after 50 feet of raceway is already installed means either upsizing the conduit or splitting the run.

EMT as an Equipment Grounding Conductor

Under NEC 250.118, properly installed EMT qualifies as an equipment grounding conductor. The metal tubing itself provides the fault-current path back to the service panel, so most branch circuits do not need a separate green or bare grounding wire pulled inside the raceway. That saves material and conduit fill space.

The condition is continuity at every joint. A single loose coupling or corroded connection breaks the grounding path, and a broken grounding path leaves a fault on the circuit with no low-impedance route back to the panel. That can leave metal enclosures energized until a breaker eventually trips, or never trips at all. Tighten every fitting, check every coupling, and use anti-oxidant compound where dissimilar metals meet.

Dissimilar Metals

Mixing metals in the conduit system creates the potential for galvanic corrosion, where one metal slowly eats away at the other in the presence of moisture. The NEC requires you to avoid dissimilar metal contact where practicable.¹ Galvanized steel fittings with aluminum EMT, or aluminum fittings with galvanized steel EMT, are permitted in areas not subject to severe corrosion. Stainless steel EMT must be paired exclusively with stainless steel fittings and accessories. Aluminum EMT running into a galvanized steel box in a damp basement is the kind of connection an inspector will look at closely.

1
National Fire Protection Association. NFPA 70 National Electrical Code – Article 358 Electrical Metallic Tubing Type EMT