Electrical Metallic Tubing Explained – EMT – Article 358

First Things First: It’s Tubing, Not Conduit

If there were a dollar for every time someone said “EMT conduit,” there’d be a very rich electrician somewhere. EMT stands for electrical metallic tubing — and that word “tubing” is deliberate. It is the thinnest-walled classification of metal, non-flexible raceway.

“If I had a dollar for everybody that says EMT conduit… then I’d be a rich man. It’s a tubing. It is not a conduit.”

Here’s how the family breaks down:

• RMC — rigid metal conduit (a raceway, a conduit)
• IMC — intermediate metal conduit (a raceway, a conduit)
• PVC — rigid polyvinyl chloride conduit (a raceway, a conduit)
• EMT — electrical metallic tubing (a raceway, but tubing)

It’s a small distinction, but the NEC organises articles around it, and exam writers absolutely know the difference.

EMT is arguably the number one or number two most-used wiring method in the trade. It goes indoors and outdoors, it’s easy to bend up to about trade size 1¼, and it’s where nearly every apprentice starts — offsets, 45s, 90s, back-to-back bends. Use compression fittings outdoors, and set-screw type is typically fine indoors unless your project specification says otherwise.

Start With the Scope — 358.1

As with any wiring method, read the scope first. Article 358 covers the use, installation, and construction of electrical metallic tubing and its associated fittings. That last part matters: this article isn’t just about the pipe, it’s about the connectors, couplings, elbows, and factory bends too.

358.6 then tells you everything has to be listed — the EMT itself, the factory elbows, and the associated fittings. There’s no room for an unlisted part in the assembly.

Transitions Between Wiring Methods

This trips people up constantly. If you’re transitioning from EMT to, say, MC cable, you need a fitting that is listed for use with EMT and evaluated and listed for MC. What you cannot do is the Frankenstein approach:

EMT → connector → threaded coupling from rigid → MC connector → clamp on the MC.

That chain is not compliant. Whatever fitting you use to make the transition has to be listed for both wiring methods it joins. The same principle applies for any other wiring method you transition EMT into.

Uses Permitted — 358.10

EMT is permitted for both exposed and concealed work. Beyond that, 358.10(A) allows it:

• In concrete, in direct contact with the earth, or in direct burial applications with fittings identified for direct burial (look for the DB marking)
• Or in areas subject to severe corrosive influences, where installed in accordance with 358.10(B)
• In dry, damp, or wet locations
• In any hazardous (classified) location as permitted by other articles
• For manufactured wiring systems as permitted in 604.100(A)(2)

Pay attention to that little word “or.” Learning to dissect the code — recognising where a requirement splits into alternatives — is one of the biggest skills you can develop. The code is slowly moving toward a numbered, broken-up format precisely because run-on sentences are hard to follow.

So yes — you can put EMT in the ground. Plenty of people insist otherwise, but galvanised steel EMT already ships with a sacrificial zinc coating that is its corrosion protection. The Steel Tube Institute (STI) publishes documentation on exactly this. Use the proper fittings for the environment (not set-screw), and you’re fine.

Corrosion: Ordinary vs. Severe — 358.10(B)

This is where the two-tier system matters:

• Corrosive environments: galvanised steel and stainless steel EMT, elbows, and fittings are permitted in concrete, in direct contact with earth, and in direct burial. The galvanisation is doing its job.
• Severe corrosive influences: now you need supplementary corrosion protection, approved as suitable for the condition — and “approved” means the AHJ signs off.

Who decides what’s “severe”? Usually the local jurisdiction, based on known soil acidity or chemical exposure. A chemical plant, a processing facility, or the chemical storage room off a pool equipment room could all get that designation.

Aluminium EMT gets called out specifically: it shall be provided with approved supplementary corrosion protection where encased in concrete or in direct burial with earth. Aluminium EMT is getting more popular — it’s lighter, which your shoulders appreciate on overhead work in the larger trade sizes — but the extra protection step is real.

Cinder Fill

Galvanised or stainless steel EMT is permitted in cinder concrete or cinder fill subject to permanent moisture only when:

1. Protected on all sides by a layer of non-cinder concrete at least 2 in. thick, or
2. Installed at least 18 in. under the fill

Wet Locations

All supports, bolts, straps, and screws must be of corrosion-resistant material or protected against corrosion. Here’s where installations fail in practice: people buy the correct listed strap and then drive it with whatever screw is in the pouch. Sheetrock screws in a wet location are a rust problem waiting to happen.

Physical Damage

Steel and stainless steel EMT is permitted where subject to physical damage — an allowance added in the 2020 cycle. It is not rated for severe physical damage. The NEC doesn’t define either term, so this is an AHJ conversation. For context, MC cable, Schedule 40 PVC, AC cable, and NM cable are not rated for physical damage; Schedule 80 PVC and EMT are.

Uses Not Permitted — 358.12

This is mandatory language. EMT shall not be used:

1. Where subject to severe physical damage
2. For the support of luminaires or other equipment, except conduit bodies no larger than the largest trade size of the tubing

That second one means your ¾ EMT can support a ¾ LB. What it can’t do is support a luminaire, or an oversized conduit body that exceeds the trade size of the raceway entering it.

3. Where practicable, dissimilar metals in contact shall be avoided to eliminate galvanic action. That said, stainless steel and aluminium fittings and enclosures are permitted with galvanised steel EMT, and galvanised steel fittings and enclosures are permitted with aluminium EMT — as long as the location isn’t subject to severe corrosive influences.

Stainless steel EMT gets its own restriction: it shall only be used with stainless steel fittings, boxes, and enclosures; or with steel (galvanised, painted, powder-coated, or PVC-coated) boxes and enclosures where not subject to severe corrosive influences; or with non-metallic or approved accessories.

Here’s a field tip on that: if an engineer has specified stainless steel EMT, look hard at why. There may be a corrosive condition driving that spec that isn’t obvious from the drawings. And if you introduce anything non-metallic into the path and it breaks your effective ground-fault current path, you need equipment bonding jumpers.

Sizes, Fill, and Bends

• Trade sizes: ½ through 6
• Number of conductors: shall not exceed the percentage fill in Table 1, Chapter 9 — the familiar 53%, 31%, and 40% figures, with Tables 4 and 5 doing the arithmetic
• Bends (358.24): shall be made so the tubing is not damaged and the internal diameter is not effectively reduced. Oblong that pipe with the wrong bender and you’ve changed the ID — no dog legs.
• Bend radius (358.24): field bends shall not be less than the centre-line radius shown in Table 2, Chapter 9, using the “One Shot and Full Shoe Benders” column. Bend tighter than that and you risk damage, jamming, and a pull that your calculation never accounted for.
• Number of bends (358.26): 360 degrees total between pull points. Add up your offsets, 45s, and 90s between boxes.

A word on that 360: if you add a pull box to stay under the limit, that box has to be sized properly to 314.28 — straight pulls at 8×, angle pulls at 6× — whether or not you ever intend to pull through it. You can’t drop in a tiny box just to satisfy the rule. A condulet works, but the length still has to meet the 8× requirement.

Reaming (358.28): all cut ends shall be reamed or otherwise finished to remove rough edges, inside and out.

Threading (358.28(B)): EMT shall not be threaded — with the exception of EMT with factory-threaded integral couplings complying with 358.100.

Securing and Supporting — 358.30

EMT shall be installed as a complete system in accordance with 300.18. That means finish the raceway run first, then pull the conductors. Not piecemeal — pull a length, add a coupling, pull again. You see this most with PVC on underground pool work, but the rule is the same for EMT.

358.30(A) — Securely Fastened:

1. At intervals not exceeding 10 ft
2. Within 3 ft of each outlet box, junction box, device box, cabinet, conduit body, or other tubing termination

On that “within 3 ft” debate — within 3 ft means anywhere from zero out to 3 ft. Three feet is within three feet. The NFPA’s own illustration shows the securement at 3 ft. Don’t let anybody spend your afternoon on the semantics.

Note also that couplings do not break the measurement. A 10 ft stick with a coupling at the end is still governed by the 10 ft interval.

Exception No. 1: Where structural members do not readily permit fastening within 3 ft, an unbroken length (no couplings) may go up to 5 ft. This is the parking-garage and open-ceiling allowance — jurisdictions sometimes make people install their own supports to hit 3 ft, but the allowance is right there in the code.

Exception No. 2: For concealed work in finished buildings or prefinished wall panels where securing is impracticable, unbroken lengths without a coupling may be fished.

358.30(B) — Supports: Horizontal runs of EMT supported by openings through framing members at intervals not greater than 10 ft, and securely fastened within 3 ft of termination, shall be permitted. Running through framing members counts as supported — it does not remove the securing requirement.

The Rest of the Article

• 358.42 — Couplings and connectors shall be made up tight. Where buried in masonry or concrete, they shall be concrete-tight (which itself confirms EMT belongs in masonry and concrete). In wet locations they shall comply with 314.15.
• 358.56 — Splices and taps shall be made in accordance with 300.15 — in boxes, not inside the raceway.
• 358.60 — Grounding. EMT shall be permitted as an equipment grounding conductor. Many of us still prefer a wire-type EGC, but the tubing is compliant.
• 358.100 — Construction. EMT shall be made of steel with a protective coating (galvanised), aluminium, or stainless steel.
• 358.120 — Marking. EMT shall be clearly and durably marked at least every 10 ft as required by the first sentence of 110.21(A).

An Exam Strategy for Short Articles

Here’s a genuinely useful test-taking habit. When you read a question and it feels specific to EMT — securing, supporting, uses permitted, uses not permitted — don’t run to the index. Article 358 is a short article. Bold scan it.

The reasoning is simple: the .10 (uses permitted) and .12 (uses not permitted) sections exist in nearly every wiring-method article, so once you’ve identified that the question is germane to EMT itself rather than a general Article 300 rule, jumping straight to 358 and scanning the bold headings is faster than working the index. The index is a great tool — it’s just the wrong tool for a two-page article.

Ask yourself: what am I trying to do here, and is EMT okay for it? That’s the starting point.

One Last Thought: You Can Change the Code

If there’s something in the NEC you find ambiguous or badly worded, the code-making panels aren’t going to go hunting for it. You submit a public input. If you can justify it and quantify it, the panel will look at it, and if it has merit, it changes. That’s how the wire-nut volume clarification in the box-fill rules got in there. Squeaky wheel gets the grease.

How NEC Mastery Fits Into This

Article 358 is exactly the kind of material that rewards repetition — the 10 ft / 3 ft securing intervals, the 360-degree bend limit, the difference between “corrosive” and “severe corrosive,” and the stainless-versus-aluminium fitting combinations all blur together until you’ve worked through them enough times.

• 8,000+ exam-style questions include raceway-specific items across EMT, RMC, IMC, and PVC, so you practise the distinctions side by side instead of studying one article in isolation
• Detailed explanations referencing specific NEC articles point you back to 358.10, 358.12, 358.30, and the Chapter 9 tables — building the same mental map that makes bold scanning work on exam day
• Timed mock exams weighted to your exam type put raceway questions in front of you under the clock, so you learn to recognise “this is a 358 question” in seconds rather than burning time in the index
• Calculation practice for raceway fill using Chapter 9 Tables 1, 4, and 5, plus bend radius checks against Table 2 — the arithmetic you’ll actually be asked to perform

Learn the structure of the article, practise until the numbers are automatic, and EMT questions become free points.