PVC vs. Metal Conduit

Conduit does one job: protect the wires running through it. Electrical conduit is a raceway designed to protect conductors from mechanical damage, moisture, and chemical exposure. The choice splits into two families — non-metallic PVC and metal — and picking wrong is how jobs fail inspection or generate callbacks down the line.

For broader project planning, explore WBC’s building materials resources.

Here’s the short version. PVC is best for moisture-prone, underground, and outdoor runs. It resists corrosion and moisture, is easy to install, and is commonly used outdoors or underground. Metal — EMT, IMC, RMC — earns its keep where you need physical protection, fire resistance, or a grounding path built into the raceway itself. For a Montana DIYer or contractor wiring out to a detached shop or burying a feeder, that distinction drives most of the decision.

One difference matters before anything else. PVC has no inherent grounding capability and requires the installation of a separate equipment grounding conductor. Metal raceway can serve that role. Where electrically and mechanically continuous, all types of metal raceway can be used as an equipment grounding conductor. They make better EGCs than wire conductors because their much larger surface area will carry high-frequency current via the skin effect.

PVC: Schedule 40, Schedule 80, and Where Each Belongs

PVC is the workhorse for anything buried or wet. PVC conduit is manufactured from thermoplastic polyvinyl chloride and is typically available in Schedule 40 for standard installations and Schedule 80 for areas requiring additional wall thickness. It is assembled using solvent cement, creating a continuous, sealed raceway.

The two schedules cover most decisions. Schedule 40 has thinner walls suitable for most buried applications, while Schedule 80’s thicker walls provide additional impact resistance required for above-ground exposed installations. Both are rated for the ground — Schedule 80 is approved for direct burial and concrete encasement — and for a residential or light-commercial run, depth matters: it is typically installed at a minimum depth of 18 inches to protect conductors from environmental exposure and physical damage.

PVC’s weaknesses are mechanical and thermal — both worth knowing in Montana. It’s brittle in cold weather, cannot be bent without heat, and is not fire-resistant. Temperature swings here are no joke, which is why the expansion rule isn’t optional on long outdoor runs. Always use expansion couplings outdoors. PVC expands and contracts with temperature swings more than most people realize. Specifically: in high-swing climates, use expansion fittings (required when runs exceed 25 feet and temperature change exceeds 60°F).

Sunlight degrades unrated PVC. Use sunlight-resistant (UV-rated) PVC for any above-ground outdoor run. Basic white PVC will chalk, embrittle, and crack if left exposed.

Beyond the standard schedules, specialty types exist for buried work. Type EB (Encased Burial) has thinner walls than both SCH 40 and 80 because it is designed to be encased in concrete, which provides the necessary external protection. And Type DB products are built for direct burial, meaning they can be installed directly into soil without the need for concrete encasement.

Metal: EMT, IMC, and RMC — Strength, Cost, and Code-Legal Locations

Metal isn’t one product. Metal conduit systems are constructed from steel or aluminum and include three primary types: RMC, IMC, and EMT. RMC is the heaviest-duty, IMC is slightly thinner, and EMT (thin-wall) is the lightest and most common in commercial work. Connection method follows the type: they are joined with threaded couplings (RMC/IMC) or set-screw/compression fittings (EMT).

EMT is the fast, affordable indoor choice. Manufactured from thin-wall steel tubing with a protective coating, EMT offers excellent mechanical protection while remaining lightweight and cost-effective. The tubing uses compression or set-screw fittings rather than threaded connections, significantly speeding installation. But know its limits: EMT is not rated for burial. If you’re going underground with metal, use RMC or IMC, and use anti-corrosion treatment at joints. The zinc coating provides adequate corrosion protection for dry, indoor environments but isn’t sufficient for direct burial or continuous wet locations.

IMC splits the difference. IMC represents the middle ground between lightweight EMT and heavy-duty RMC. With walls approximately 25% thicker than EMT but lighter than RMC, IMC provides enhanced mechanical protection while maintaining reasonable weight and installation efficiency. It’s also approved for use in all locations where RMC is permitted.

RMC is the tank. RMC is typically composed of heavyweight galvanized steel and installed with threaded fittings. Both RMC and IMC carry no real location restrictions — IMC and RMC can be used in all atmospheric conditions and occupancies. They can also be used where subjected to physical damage, while no other metal raceway can be used under this condition.

Type	Wall / Build	Connection	Best Fit
EMT	Thin-wall steel	Set-screw / compression	Dry indoor runs; not for burial or physical-damage areas
IMC	~25% thicker than EMT, lighter than RMC	Threaded	Anywhere RMC is allowed; exposed runs needing protection
RMC	Heaviest galvanized steel	Threaded	Maximum protection, hazardous locations, physical damage
PVC Sch 40	Standard wall	Solvent cement	Most direct-burial and underground runs
PVC Sch 80	Thicker wall	Solvent cement	Exposed above-ground, high-impact areas

On trade sizes, EMT is available in trade sizes from 1/2 inch through 4 inches, while PVC is manufactured in standard 10-foot lengths and available in sizes from 1/2 inch through 6 inches and larger for specialized applications. Western Building Center’s PVC Schedule 40 lineup runs from 1/2-inch up through 3-inch in 10-foot sticks, with EMT carried in 1/2-inch and 3/4-inch. Flexible options include ENT and nonmetallic liquidtight in 1/2-inch and 3/4-inch, plus aluminum flex.

Matching Conduit to the Application

The job site decides. No single conduit type is appropriate for every application. Contractors and engineers select conduit based on exposure conditions, code requirements, and total installed cost rather than relying on a single system across the entire project.

For buried runs out to a garage or shop, PVC wins. PVC conduit is the standard choice for underground installations because it is inherently corrosion-resistant and approved for direct burial. Metal conduit is generally avoided in these conditions due to its susceptibility to corrosion and higher cost unless specific protection requirements justify its use.

For dry interior work, EMT is the default. EMT is the dominant conduit in commercial interiors because it balances cost, installation speed, and performance. Its ability to serve as the equipment grounding conductor eliminates the need for an additional grounding wire.

For exposed outdoor runs where something might hit the conduit, the question is corrosion versus impact. PVC won’t rust; metal takes a beating. In areas where conduit takes physical abuse, metal’s longer life and impact resistance may pay off in fewer repairs. Steel conduit stands up to collisions, kicks, and weed trimmers. PVC cracks where metal dents. Some jurisdictions force the call — some municipalities require Schedule 80 PVC for exposed areas, while others demand metal for any conduit under 8 feet off the ground.

The smart hybrid is common. Many pros run PVC underground, then switch to EMT or RMC above ground using rated transition fittings. It meets code, cuts costs, and gets the job done right.

One thing the temperature data reinforces for this climate: metal holds a wider range. PVC loses strength in high heat and can become brittle in extreme cold. Its code-listed ambient max is 122°F. Metal holds up across a wider range and doesn’t expand or contract as dramatically. PVC’s listed band runs roughly -4°F to 122°F ambient, while metal spans about -40°F to 140°F+.

Whatever you choose, confirm it locally. Don’t guess — call your AHJ (Authority Having Jurisdiction).

Installation Basics That Pass Inspection

Right material, wrong install, still fails. A few rules carry most jobs.

Support spacing. Max 3 ft for ½–1” PVC (NEC 352.30); up to 10 ft for EMT (NEC 358.30).

Bends. The total of bends (including offsets) between pull points cannot exceed 360°.

Expansion. On long PVC, allow for movement: use 3/8 inch of movement per 10 feet of run for every 100°F temperature differential.

Connections. PVC gets solvent cement; metal gets mechanical or threaded fittings. And no mixing parts across systems — each type of metal raceway and its associated fittings must be listed. None of them is interchangeable among types. When you cut metal in the field, reaming (nonflexible) or trimming (flexible) is required to remove the rough edges.

Don’t overtighten. This does not mean crank down as hard as you can. You tighten the coupling for EMT only enough to make a slight dimple in the tubing. Going beyond this could distort the tubing wall, adding excess friction for a conductor pull.

A field habit worth adopting: oversize when possible — one trade size up eases wire pulls and supports future upgrades.

Frequently Asked Questions

Does PVC conduit need a ground wire? Yes. PVC has no inherent grounding capability and requires the installation of a separate equipment grounding conductor, increasing the conductor count. Metal raceway, when continuous, can serve as the grounding path itself.

Can EMT be buried? No. EMT is not rated for burial. If you’re going underground with metal, use RMC or IMC, and use anti-corrosion treatment at joints. For buried runs, PVC Schedule 40 or 80 is the standard, installed at a typical minimum depth of 18 inches in residential and light-commercial work.

Can I transition from PVC underground to metal above ground in the same run? Yes. Use listed transition fittings with gaskets and sealant to maintain water-tightness and bonding continuity. Running PVC in the trench and switching to EMT or RMC above grade is a common, code-compliant approach.

What’s the difference between Schedule 40 and Schedule 80 PVC? Wall thickness. Schedule 40 has thinner walls suitable for most buried applications, while Schedule 80’s thicker walls provide additional impact resistance required for above-ground exposed installations. Both are approved for direct burial.

Why does PVC need expansion fittings outdoors? Because plastic moves more than people expect with temperature. In high-swing climates, use expansion fittings — required when runs exceed 25 feet and temperature change exceeds 60°F. With the kind of seasonal swings seen across Montana, that threshold gets crossed on most long outdoor runs.

Will basic gray PVC hold up in the sun? Not for long. Use sunlight-resistant (UV-rated) PVC for any above-ground outdoor run. Basic white PVC will chalk, embrittle, and crack if left exposed.