Electrical conduit is required whenever wiring needs physical protection, moisture resistance, or a clean path through exposed areas. In most residential and commercial settings, you’ll use conduit for any wiring that runs along the surface of walls, through unfinished spaces like basements and garages, outdoors, or underground. National Electrical Code (NEC) requirements and local building codes dictate specific situations where conduit is mandatory rather than optional.
Where Building Codes Require Conduit
The NEC requires conduit in several specific scenarios. Any wiring exposed on the surface of a building, rather than hidden inside walls, must be protected by conduit. This includes wires running along basement ceilings, garage walls, and the exterior of a structure. Commercial buildings generally require conduit throughout, while residential codes are more lenient about using nonmetallic cable (Romex) inside finished walls.
Underground wiring almost always requires conduit, though the type and burial depth vary. Wiring in areas subject to physical damage, such as a workshop where equipment could strike an exposed cable, also needs conduit protection. Some municipalities go beyond NEC minimums. Chicago, for example, requires metal conduit for nearly all residential wiring, while most other cities allow Romex inside walls and ceilings.
Common Situations for Each Conduit Type
EMT (Electrical Metallic Tubing)
EMT is the thin-walled metal conduit you see most often in commercial buildings, unfinished basements, and garages. It’s lightweight, easy to bend, and relatively affordable. Use EMT for indoor exposed runs where you need code-compliant protection but aren’t dealing with moisture or underground burial. It connects with compression or set-screw fittings rather than threading, making it faster to install than rigid conduit. EMT is not rated for direct burial or areas with heavy physical impact.
Rigid Metal Conduit (RMC) and IMC
Rigid metal conduit has thick walls and threaded connections, making it the strongest option. It’s used where wiring faces serious physical threats: industrial environments, outdoor installations exposed to impact, and some underground applications. Intermediate metal conduit (IMC) offers similar protection with thinner walls and lighter weight, making it easier to work with while still meeting requirements for areas needing heavy-duty protection.
PVC Conduit
PVC is the go-to choice for underground runs and outdoor installations where corrosion is a concern. It resists moisture, chemicals, and soil conditions that would degrade metal over time. Schedule 40 PVC works for most underground and embedded-in-concrete applications, while Schedule 80 PVC, with its thicker walls, is required when the conduit emerges from the ground and is exposed to potential impact. PVC is also significantly cheaper than metal options, which matters on long outdoor or underground runs.
Flexible Metal Conduit (FMC) and Liquidtight
Flexible conduit handles the short, awkward connections where rigid conduit can’t easily reach. The most common use is the final connection to equipment that vibrates, like HVAC units, motors, or garbage disposals. Flexible metal conduit works in dry indoor locations. Liquidtight flexible conduit adds a waterproof jacket and is the standard choice for outdoor equipment connections, rooftop HVAC units, and anywhere the flexible section will encounter moisture.
Outdoor and Underground Wiring
Any wiring running outside your home or building needs conduit for protection against weather, UV exposure, animals, and physical damage. For above-ground outdoor runs, PVC or rigid metal conduit are both acceptable, though PVC is more popular because it won’t rust. All outdoor conduit runs need weatherproof fittings and boxes rated for wet locations.
Underground wiring has specific burial depth requirements that change depending on the conduit type. PVC conduit with individual wires inside typically needs to be buried at least 18 inches deep. Rigid metal conduit can be as shallow as 6 inches. Direct-burial cable without any conduit requires 24 inches of cover. These depths explain why many homeowners choose conduit for underground runs: it lets you bury the trench shallower, which saves significant digging effort on long runs to detached garages, sheds, or outdoor lighting.
When Conduit Is Optional but Smart
Beyond code requirements, conduit makes sense in several practical situations even when it isn’t strictly mandated. If you’re running wiring through an area you might remodel later, conduit lets you pull new wires without opening walls. A few strategically placed conduit runs during initial construction can save thousands of dollars in future renovation costs.
Home workshops and hobby spaces benefit from conduit even when code might allow exposed Romex. Tools, materials, and equipment moving through the space can easily nick or damage unprotected cable. The same logic applies to wiring in agricultural buildings, storage areas, and anywhere heavy objects get moved around regularly.
Conduit also gives you upgrade flexibility. If you’re wiring a home office or media room, running conduit means you can later pull additional circuits, data cables, or higher-capacity wiring without any demolition. The conduit acts as a permanent pathway, and swapping or adding wires inside it is straightforward.
When You Don’t Need Conduit
Inside finished walls, floors, and ceilings of most residential buildings, nonmetallic cable (Romex) is perfectly code-compliant and far easier to install. The wall materials themselves provide the physical protection that conduit would otherwise offer. Attic spaces with limited access and interior wall cavities are standard Romex territory in most jurisdictions.
Low-voltage wiring for doorbells, thermostats, landscape lighting, and speaker systems generally doesn’t require conduit either, though you may still want it for protection in exposed areas. The exception is when low-voltage wiring shares a space with line-voltage wiring, where separation requirements or conduit may apply.
Sizing and Fill Limits
Conduit has strict limits on how many wires you can run inside it. This isn’t just about physical space. Too many wires packed together generate heat that can degrade insulation and create fire hazards. The general rule is that wires should occupy no more than 40% of the conduit’s interior area when you’re pulling three or more conductors.
For most residential circuits using standard 12- or 14-gauge wire, 3/4-inch conduit handles typical runs comfortably. Larger circuits feeding subpanels, electric vehicle chargers, or heavy appliances may require 1-inch or larger conduit. Online conduit fill calculators make it easy to check whether your planned wire count fits within the allowed capacity for a given conduit size. Oversizing slightly is always better than discovering mid-project that you can’t fit everything you need.