Conduit Systems

What Is a Conduit System?

A conduit system is a protective raceway that encloses and routes electrical wiring between equipment, junction boxes, and termination points. Instead of running cable out in the open, crews pull conductors through a rigid or flexible tube. Depending on the material selected and the governing code, that tube can shield the wiring from physical impact, moisture, chemical exposure, and, in some environments, the risk of ignition.

On an industrial site, conduit systems organise how power and signal cables move through a plant, protect that wiring for decades of service, and give inspectors and maintenance crews a predictable, code-compliant path to follow. Get the type or sizing wrong, and it shows up later in installation cost, long-term reliability, and how easily the facility can add cable down the road.

Common Types of Conduit Systems

Four conduit types are the standard options for industrial installations: Rigid Metal Conduit (RMC), Intermediate Metal Conduit (IMC), Electrical Metallic Tubing (EMT), and PVC. Each offers a different balance of mechanical protection, corrosion resistance, weight, and cost.

Rigid Metal Conduit (RMC)

Rigid Metal Conduit (RMC) ranks as the heaviest-duty of the common metallic types. It’s commonly made from galvanised steel, though stainless steel and aluminium versions also exist. Thick, threaded walls make it a common specification anywhere wiring needs a high level of mechanical protection, subject to the applicable code and area classification, cases like exposed outdoor runs, areas with vehicle traffic, and locations where the conduit itself might take a hit. Because its fittings are threaded rather than compression-fit, RMC can also serve as part of the equipment grounding path where code permits and every joint maintains continuous contact. The tradeoff is straightforward: RMC is heavier and pricier to install than the thinner-walled options that follow.

Intermediate Metal Conduit (IMC)

Intermediate Metal Conduit (IMC) sits between RMC and EMT in wall thickness. It is also threaded and made of steel, which gives it much of RMC’s mechanical protection and grounding performance at a lighter weight. Installed cost varies by market, labour rates, and project specifics, but IMC is commonly positioned as the lower-cost alternative to RMC for general industrial use. Some owner specifications call for RMC specifically, so it’s worth confirming project requirements before substituting one for the other.

Electrical Metallic Tubing (EMT)

Electrical Metallic Tubing (EMT), sometimes called “thin-wall” conduit, is the lightest metallic option. It is unthreaded, with fittings that attach by set-screw, compression, or indentation-type connectors. Those fitting types tend to make it quicker and less costly to install than threaded alternatives, though actual cost and labour time depend on the project. EMT is commonly used for indoor, light-industrial wiring where mechanical damage risk is low (think control rooms, equipment rooms, or covered process areas), but suitability always depends on the adopted code, the physical-damage determination for that location, and any applicable hazardous classification.

PVC (Rigid Nonmetallic) Conduit

PVC conduit trades metal’s mechanical strength for corrosion resistance. As a plastic, it does not rust, pit, or corrode like metal, making listed PVC a common choice for underground duct banks, direct burial, and many wet or chemically active environments, including coastal sites, wastewater facilities, and areas near process chemicals. Chemical compatibility depends on the specific reagent, temperature, and product listing, so check unusual exposures against the manufacturer’s data. PVC does not provide a grounding path on its own, so wherever the system requires an equipment grounding conductor, it has to run separately inside the conduit. PVC is also more susceptible to impact damage than metal conduit, and in exposed applications it can degrade under UV exposure over time unless it carries a sunlight rating.

Flexible Metal Conduit

Flexible metal conduit (FMC) and its liquidtight variant (LFMC) are built to handle movement and vibration that rigid conduit can’t. That makes them the standard choice at a motor connection, a transformer connection, or anywhere else equipment shifts slightly during operation. Some applications carry code-specific length limits, so it’s worth checking the governing code rather than assuming a blanket restriction on run length. Most installations still use FMC and LFMC at the transition points between fixed conduit and vibrating equipment, rather than as the primary raceway for an entire run.

Comparing the Main Conduit Types

Type	Material	Wall Thickness	Fittings	Typical Use
RMC	Steel (stainless and aluminium also available)	Heaviest	Threaded	Outdoor, high-impact, hazardous locations
IMC	Steel	Medium-heavy	Threaded	General industrial, cost-effective alternative to RMC
EMT	Steel (thin-wall)	Light	Set-screw / compression/indentation	Indoor, light industrial
PVC	Rigid plastic	N/A	Solvent-welded / threaded adapters	Underground, corrosive or wet environments
FMC / LFMC	Steel (flexible)	N/A	Flexible connectors	Motor connections, vibration-prone equipment

Choosing the Right Conduit Type

The short version: conduit selection depends on three factors: environmental exposure, mechanical protection needs, and area classification. In practice, these factors interact, and a useful rule of thumb is that the most restrictive factor for a given run tends to drive the decision, though the applicable code and any product listing requirements can add constraints beyond these three.

Environmental Exposure

Steel conduits (RMC, IMC, EMT) can be specified with corrosion-resistant coatings for outdoor or mildly corrosive environments, though actual service life depends on the coating system, the product listing, and the specific exposure. In consistently wet, chemically aggressive, or coastal conditions, PVC is commonly considered the lower-maintenance option, for the reasons covered above, subject to the same listing and AHJ requirements.

Mechanical Protection Needs

When impact risk is the deciding factor rather than moisture or classification, the type choice follows the same pattern covered above: RMC or IMC under real impact risk, EMT once that risk drops away.

Hazardous Locations and Area Classification

On industrial sites that handle flammable gases, vapours, or combustible dust (refineries, gas processing plants, upgraders), conduit selection also follows area classification. In Canada, this means the Class/Division system (Class I, II, or III, with Division 1 or 2), or, for Class I locations specifically, the Zone system (Zone 0, 1, or 2) as an alternative, both recognised under the CEC (CSA C22.1). The U.S. NEC uses a comparable two-system structure for Class I locations. These classifications describe the type of hazardous material present and how likely a flammable atmosphere is to occur, based on factors like release sources and ventilation. Depending on the specific class, division or zone, and equipment group, they can drive requirements for explosion-proof enclosures, explosion-proof conduit fittings, and sealing fittings designed to limit gas migration between areas. In many classified locations, codes prescribe or favour threaded metallic conduit over EMT or PVC, though permitted wiring methods vary by the specific classification, so the applicable code should always be checked for a given area.

Getting area classification wrong can be a costly mistake on a capital project, since it may not surface until commissioning or inspection, well after the conduit is already installed. A full walkthrough of Class/Division and Zone classification is beyond the scope of this article, but classification should inform wiring methods and equipment selection early in the design process, rather than being treated as an afterthought bolted onto conduit selection later.

Conduit Sizing, Fill Percentage, Conductor Count, and Pulling Tension

Selecting the right conduit type is only half the job. The other half is sizing it correctly. That comes down to three calculations: how much of the conduit’s interior the conductors can fill, how many conductors of what size have to fit, and how much tension the cable can safely take while it is pulled in.

Conduit Fill Percentage

Conduit fill percentage limits how much of a conduit’s cross-sectional area the conductors inside it can occupy. The U.S. NEC sets this at up to 53% for a single conductor, 31% for two conductors, and 40% for three or more. CSA C22.1 governs the equivalent Canadian requirement. Project teams should confirm the exact percentages in the current adopted edition, since this article has not independently verified that the Canadian figures match the NEC’s.

Number of Conductors	Maximum Fill (NEC)
1	53%
2	31%
Over 2	40%

These limits generally leave clearance for conductors to be pulled in without damaging their insulation and help manage heat generated by the conductors. Exceeding these limits is a common reason a conduit installation fails inspection, and it is also one of the easier problems to avoid. Check fill percentage against the actual conductor sizes and count before ordering the conduit, not after it is already in the ground or behind a wall.

Trade Sizes and Conductor Quantity

Conduit comes in standard trade sizes. Common product lines span roughly 1/2 inch up to 6 inches, though the exact range and available increments vary by conduit type and manufacturer. Working out the required trade size starts from the number and gauge of conductors that need to fit inside it at the applicable fill percentage, though conductor insulation dimensions, any grounding conductors, jam ratio, and code exceptions can also affect the final size. On projects where future circuits are likely, some specifications call for a trade size one or two increments larger than the bare minimum, on the reasoning that this small bit of upsizing now can be cheaper than pulling in a parallel conduit run later, though the actual cost comparison depends on the project.

Pulling Tension and Bend Limits

Pulling tension is the force applied to a cable as it moves through conduit, and the maximum a cable can safely take depends on how it’s built. Exceed it, and you risk stretching or damaging the conductors and their insulation. Tension builds with the length of the pull, the number and severity of bends, and the bend radius at each point. Friction between the cable jacket and the conduit wall adds to it too. A compatible lubricant can help reduce that friction, though the effect depends on the specific cable and conduit materials. Codes also cap the total degrees of bend allowed between two pull points, commonly no more than 360 degrees total, or four quarter bends. Once a run reaches that limit, it needs a pull point, which can be a pull box, a conduit body, or another approved fitting, to relieve the built-up tension before continuing.

Planning for Future Cable Accessibility

Sizing decisions should also account for future cable accessibility, not just current need. In practice, this means sizing conduit and placing pull boxes with spare capacity, so the facility can add instrumentation, controls, or power circuits later without cutting into walls, floors, or paved areas. Whether that goal is met depends on the route, access, remaining fill capacity, and the specific circuits added later.

Codes and Standards at a Glance

In Canada, conduit systems are governed by the CEC (CSA C22.1), which is adopted and enforced by provincial and territorial electrical safety authorities. Separately, engineering services on projects like these fall under the oversight of provincial engineering regulators, including APEGA in Alberta, which governs the practice of professional engineering rather than the electrical code itself. The U.S. equivalent code is the NEC (NFPA 70). In general terms, the two codes share similar fundamentals around fill percentages, bend limits, and area classification concepts, though they differ in section numbering, terminology, and some material approvals, and the specific edition adopted, the facility’s location, and any contractual requirements all affect which provisions apply. Canadian code requirements govern for any project delivered in Canada, subject to the adopted provincial edition and the local authority having jurisdiction.

Projects that cross the border, or that involve engineers licensed in both countries, need to confirm which code governs a given facility. Provincial and municipal authorities having jurisdiction may also add requirements of their own, particularly around inspection and hazardous location permitting. Always verify specifics with the relevant provincial authority before finalizing a design.

Certifications and licensure requirements vary by jurisdiction. This article reflects Canadian standards and Alberta provincial regulations. For projects in other provinces or jurisdictions, verify requirements with the appropriate provincial authority having jurisdiction.

Installation Practices Site Teams Should Know

Even a correctly specified conduit system can run into trouble in the field if installation practices are inconsistent. A few practical points make an outsized difference:

• Support spacing. Conduit needs support at regular intervals, or it can sag, stressing fittings and potentially creating spots where moisture collects. Spacing requirements vary by conduit type, size, and orientation, so it is worth checking the applicable code table rather than relying on habit.
• Expansion fittings. Long outdoor conduit runs expand and contract with temperature swings. Expansion fittings, placed at intervals determined by the material, the expected temperature range, and any fixed points in the run, accommodate that movement so it doesn’t stress joints and connections over time.
• Bend radius. Bends that are tighter than the cable manufacturer’s minimum bend radius increase pulling tension and risk damaging conductor insulation, even when the bend technically fits within the space available.
• Grounding continuity. Metallic conduit (RMC, IMC, EMT) can serve as part of the equipment grounding path, but only if every joint keeps continuous, low-resistance contact. See the FAQ below for when that applies.

Conduit vs. Cable Tray and Other Raceway Methods

Conduit is not the only way to route electrical wiring, and it is worth knowing when an alternative makes more sense. Cable tray is a common consideration on large industrial facilities with many parallel cable runs, since it can be faster to install and easier to add cable to later, though it offers less mechanical and environmental protection than enclosed conduit unless it’s covered. Whether tray or conduit makes more sense for a given project depends on cable type, layout, environment, labour availability, and any hazardous-area requirements. Direct-buried cable, run underground without conduit, can reduce material cost for some utility and distribution applications, depending on burial depth, soil conditions, and the applicable code. But it gives up the physical protection and future accessibility that conduit provides, a real consideration on any site expecting future expansion.

Frequently Asked Questions

What’s the difference between EMT and rigid metal conduit?

EMT is thin-walled, unthreaded, and connects with set-screw, compression, or indentation-type fittings, which tends to make it lighter and quicker to install. RMC has thick, threaded walls, most commonly steel, that provide more mechanical protection and, where code permits, a more dependable grounding path. Installed cost for RMC tends to run higher than for EMT, though this varies by project. EMT is commonly used indoors or in low-risk areas. RMC is used where impact protection or hazardous location requirements call for it.

What is the maximum fill percentage allowed in a conduit?

The U.S. NEC sets this at up to 53% for a single conductor, 31% for two conductors, and 40% for three or more. CSA C22.1 governs the equivalent Canadian requirement. Confirm the exact percentages in the current adopted edition. These limits, in general, are meant to leave room to pull conductors in without damaging the insulation, and to help manage heat.

Can PVC conduit be used underground or direct-buried?

Yes, when listed for the application. PVC’s corrosion resistance makes it a common choice for underground duct banks and direct burial. Because PVC is nonmetallic, wherever the system needs an equipment grounding conductor, it has to run separately inside the conduit, unlike some metallic conduit installations where the raceway itself can serve that role.

Is intermediate metal conduit the same as rigid metal conduit?

No. IMC and RMC are both threaded conduit, most commonly steel, but IMC has thinner walls, which makes it lighter while still providing much of the same mechanical protection. Installed cost for IMC tends to run lower than for RMC, though this depends on the project and market. IMC is commonly specified as a substitute for RMC, though some owner specifications or high-impact locations still call for RMC specifically.

Does conduit need a separate ground wire, or can it serve as the grounding path?

Metallic conduit (RMC, IMC, or EMT) can serve as an equipment grounding conductor under specific code conditions, provided every joint keeps continuous, low-resistance contact. PVC conduit cannot do this. Wherever the system requires an equipment grounding conductor, it has to be pulled in separately.

The Bottom Line

Type selection and sizing are really two sides of the same decision. Choosing RMC, IMC, EMT, or PVC sets the physical and environmental limits of a conduit system. Fill percentage, trade size, and pulling tension determine whether that conduit system can be installed, and lived with, over the life of the facility. Getting both right, especially on a site with hazardous location requirements, comes down to weighing exposure, protection, code, and future need against each other for every single run.

On complex industrial and capital projects, refineries, gas processing plants, and heavy oil facilities among them, that kind of decision-making runs through the entire electrical design, not just the conduit. Vista Projects’ electrical and instrumentation and controls engineering teams handle exactly this scope of work, including area classification and hazardous location design, as part of integrated, multi-discipline project delivery.