If you're procuring wire and cable for a construction or infrastructure project, conduit isn't always your decision, but understanding when it's required helps you ask the right questions, spec correctly, and avoid costly rework.

Here's a plain-language breakdown of the NEC rules on conduit: cases when you need to use it, and when you don't.

When Conduit Is Required

Exposed outdoor wiring must use a method rated for wet locations and physical damage. Running cable along an exterior wall without protection doesn't meet code. Wet-rated conductors like THWN-2 still need additional protection. For most outdoor-exposed runs, EMT with weatherproof fittings is the minimum, but RMC is the better choice for harsher environments.

Underground runs require conduit unless the cable itself is listed for direct burial (like UF or USE-2). PVC Schedule 40 is the standard choice for most underground installations — it handles moisture, is chemically resistant, and is easier to pull through than metal. Where physical damage is a concern at or near grade level (a parking lot, a road crossing), step up to Schedule 80 or RMC. Burial depth requirements vary: generally 24 inches for direct burial, 18 inches for RMC, and 6 inches under a concrete slab.

Even direct burial cable must be protected with conduit where it transitions above grade.

Hazardous locations: areas with flammable gases, vapours, or combustible dust. They typically require RMC or IMC under NEC Articles 500 through 516. The classification tier (Class I, II, or III; Division 1 or 2) determines exactly which conduit types are permitted. If your project touches a refinery, chemical plant, grain facility, or similar site, the conduit spec must be based on the hazard classification.

Service entrance conductors running from the utility meter to the main panel typically require a raceway under NEC Article 230.43. RMC or IMC is common here for the exterior portion; EMT is generally acceptable once inside. Confirm with the utility, as they often have their own requirements in addition to NEC.

Wiring subject to physical damage: in garages, machine rooms, warehouses, loading docks, or anywhere cable runs in areas with vehicle or equipment traffic, conduit is required. EMT is acceptable in many of these environments; RMC or IMC is recommended anywhere impact risk is higher.

Exposed non-residential commercial and industrial wiring commonly requires conduit. In commercial construction, EMT is the workhorse for most exposed-branch-circuit wiring. Industrial environments often call for RMC or IMC, where mechanical protection is a priority. Some jurisdictions allow MC cable as an alternative in commercial applications.

When Conduit Is NOT Required

NM cable (Romex) in concealed spaces: NM cable is permitted in concealed walls and ceilings of wood-framed residential buildings under NEC Article 334 behind the walls or in drywall. It's fast to install and cost-effective in the right setting. The structure provides the protection, making the conduit irrelevant. The keyword here is concealed: the moment NM runs exposed (along a basement ceiling, down a garage wall), it needs protection. NM is also not permitted for commercial or industrial applications. If a project spans residential and commercial space, confirm which rules apply floor by floor.

Note that if the project involves renovation or tenant fit-out work in a space likely to be reconfigured, running conduit even where it isn't required makes future rewiring dramatically easier.

MC and AC armored cable carry their own metal jacket, which serves as a conduit in most exposed locations. MC cable (Article 330) is the more versatile of the two: it's permitted in most occupancies, in wet locations with the right jacket type, and in direct burial configurations when listed for it. AC cable (Article 320) is more restricted and primarily used in residential and light commercial work. For procurement: if the spec calls for armored cable as a conduit substitute in an exposed commercial run, confirm it's MC and not AC, and verify the jacket rating matches the environment.

Direct-burial cable UF or USE can be installed in the ground without conduit when installed at the correct burial depth per NEC Article 300.5. UF cable is the standard for residential branch circuits to outbuildings, landscape lighting, and other low-complexity outdoor runs. USE is used for service entrance conductors and higher-voltage applications. Both are rated for moisture and soil contact, but neither handles physical damage at grade well. If the run crosses a driveway, passes through landscaped areas with future digging risk, or serves critical infrastructure, THWN in conduit is the

Low-voltage wiring for data, telecom, HVAC controls, and Class 2 circuits is often exempt from conduit requirements under NEC Articles 725, 800, and 830. However, many commercial and institutional projects specify conduit for low-voltage runs anyway to make future upgrades easier. In data centre and critical facility work, especially, conduit for structured cabling.

Where Local Jurisdictions Change the Rules

The NEC is a minimum standard. Local authorities (AHJs) can make it stricter.

Example 1: California — Rooftop Conduit

• NEC allows sunlight-resistant wiring to be exposed

• California requires a conduit for all rooftop runs because of extreme heat and UV degradation.

Example 2: Florida — Coastal Protection

• NEC allows certain outdoor wiring methods

• In the High-Velocity Hurricane Zone — Miami-Dade and Broward Counties — conduit must resist hurricane uplift forces. These requirements appear in Florida-specific amendments, not the base NEC. Salt corrosion is a real concern in coastal installs, and PVC is standard practice over EMT near the ocean, but the formal code driver is wind zone classification.

How to Check Conduit Requirements Locally

To get the correct answer for your project:

1. Identify the AHJ (local building department)

2. Confirm which NEC version is adopted

3. Review local amendments

4. Check installation guides or inspection checklists

5. Contact the inspector if needed.

Conduit Types To Match the Environment

• EMT — indoor exposed runs

• PVC — underground and wet locations

• RMC / IMC — heavy-duty and hazardous

• FMC / LFMC — flexible equipment connections

Nassau National Cable supplies all major cable types used in conduit systems, whether you're working on residential, commercial, industrial, or utility-scale projects.

These include:

• THHN / THWN-2 for general-purpose conduit wiring

• XHHW / XHHW-2 for higher temperature and wet-location performance

• RHH / RHW-2 for heavy-duty power distribution

• USE-2 for underground and service entrance applications

• MTW wire for control panels and machine wiring

• DLO cable for flexible power leads in conduit or raceway

• Tray cable (TC-ER) for industrial and exposed tray systems

• MC cable for armored, conduit-free alternatives where permitted

• UF cable for direct burial residential runs

• Service entrance cable (SER/SEU) for feeder and service applications

• Portable power cables (Type W, SOOW) for temporary and flexible installations

• Medium voltage cables (MV-90 / MV-105) for utility and large-scale systems