This electrical conduit guide goes over the application of different conduit types. Also included are helpful install tips.
I’m going to discuss the following four conduit types:
- EMT (Electrical Metallic Tubing)
- GRC (Galvanized Rigid Steel Conduit)
- FMC (Flexible Metal Conduit)
- PVC (Polyvinyl Chloride)
To point out, electrical conduits can be rigid or flexible. They also come in different types of materials like metal, aluminum, PVC, or steel. The choice depends on the install application. And by making the correct choices, installations simplify and maintenance reduces.
Now, before going over each conduit type, we’ll first go over general conduit tips and tricks. This will lay the foundation for our discussion.
Important Note: for any electrical work, use the latest National Electrical Code (NEC). It’s your go-to source of information, for how to install electrical infrastructure per code. Then also, call your local building department to check for any locally enforced codes.
General conduit tips for every project
These are tips I’ve gathered over the years working on different engineering projects. Use them for both industrial and residential projects.
Tip #1: Draw schematic plan views
Before you pick up any tools, draw yourself a conduit plan. The benefits are the following:
- Knowing the type and length of conduits you’ll need
- Determining the practicality of your design
- Figuring out where you’ll need to place junction boxes in your conduit runs
- Avoiding digging into existing conduits and piping underground
Important Note: call your local utility company and 811 to find where the buried pipes are. This way, you don’t accidentally hit a gas and/or electric line.
Tip #2: Conduit sizing
Size your conduit per the number of wires pulled through it. As your guideline, use NEC Chapter 9, Table 1:
|Number of Conductors in Conduit||Maximum Fill Allowance|
Important Note: for long conduit runs, go up one conduit size. This will make your installation and maintenance easier. Especially, if you have a couple of 90° degree bends in your run.
Also, keep your minimum conduit size to 3/4 inches, to simplify wire pulling.
Tip #3: Limit conduit bends
NEC 358.26 limits the total number of bends to 360° in total between pull points. I suggest limiting the number of directional changes to no more than 270°. This makes installation and future maintenance easier, especially when pulling large conductors.
Important Note: avoid bends and offsets where possible. But when necessary, make your turns using fittings. Then as a last resort, make bends with an approved hickey or conduit bending machine.
Tip #4: Use conduit supports
Secure all conduits and fittings on exposed surfaces with clamp backs and channels or struts. The spacing of conduit supports is to be as required by the National Electrical Code, but do not exceed 4 ft. Refer to NEC 358.30.
Tip #5: Use conduit fittings
Unthreaded fittings fall into the two following categories:
- Gland (compression) type
- Set-screw type
The gland type is the only unthreaded fitting type you can use in wet locations.
For non-wet locations, join conduits together using threadless set-screw couplings. The end pieces of conduits go inside either end of the couplings. You then tighten the coupling with set screws.
The following are other common fittings you should use and why:
- Expansion fittings: use in areas with large temperature swings. This will limit stress damage on conduits from expansion and contraction.
- Ground fittings: use where conduit breaks happen to ensure ground continuity. This fitting creates a jumper path around any discontinuities in a ground path.
- Elbows: used for 90° conduit direction changes.
- Drain: use in areas with temperature swings, where condensation is a possibility. Install a drain at the lowest point of a conduit run, where water may gather.
Tip #6: Pre-bent conduits and fittings
Use pre-bent conduits and fittings to simplify your work and establish quality control. It’s always best to do the least amount of self-bending to avoid damage.
Tip #7: Cutting and reaming conduits
You can cut certain conduits using a hacksaw. But after cutting, be sure you ream and smooth the edges. You want to avoid sharp conduit edges, which can damage pulled wires.
Tip #8: Through the wall and roof conduit penetrations
- Install wall seals, for all conduits penetrating walls
- Install expansion and deflection fittings, where conduits cross-building expansion joints
- Make roof penetrations watertight with weatherproof hot-dipped galvanized sheet metal flashing caps
Tip #9: Ideal underground and aboveground conduit types
For the most long-lasting installations, use the following conduit types:
Underground: use nonmetallic Schedule 40 high-impact polyvinyl chloride for underground conduit installations. Conduits are to be UL approved for direct burial or concrete encasement. Fittings used with PVC conduit to be PVC solvent weld type.
Important Note: underground to aboveground 90° elbows and risers to be PVC coated GRC. I expound on this further here.
Aboveground: use rigid steel conduits for aboveground installations. The raceways need to conform to ANSI 1 C80.1. Apply zinc coating to the inside and outside of the conduit by hot-dip galvanizing after threading.
Tip #10: Symmetrically installed exposed conduit raceways
Run all conduits on exposed surfaces at right angles to and/or parallel to the surrounding walls. Also, conform exposed conduit runs to the form of ceilings.
EMT (Electrical Metallic Tubing)
What is EMT? It’s not technically a conduit, but a tubing.
You can thread EMT, but typically you assemble EMT through couplings and connectors. You attach conduit pieces together using set screws or compression glands. This makes for inexpensive, quick, and easy installations compared to threaded metallic conduits.
Where should you use EMT? typically used only indoors. It’s too thin to install underground as it’ll easily damage. So do NOT install EMT underground.
Even indoors, be careful to not install it anywhere where it’s subject to physical damage. Ideally, install EMT only in the following locations:
- Inside of walls
- In offices and corridors
In the above locations, EMT is a better choice than GRC, which we’ll discuss next, due to cost-savings alone.
Important Note: when possible, color code the EMT inside your building. Choose a different color for 480V, 120V, and 24V wiring. This helps with maintenance work.
GRC (Galvanized Rigid Steel Conduit)
What is GRC? It’s a thick wall conduit. It can have threaded ends coupled with threaded fittings, while also being threadless.
To point out, Rigid Metallic Conduit (RMC) is a generic term and GRC is a specific term. And RMC is commonly called “rigid.”
Also, you can buy steel, stainless steel, and aluminum RMC. While GRC is the most common conduit, which is of galvanized type.
Important Note: you can buy metal conduits made of aluminum and stainless steel. If a spec reads “GRC” though, it specifically refers to a galvanized rigid conduit.
Now if a spec only reads “RMC”, the conduit selection isn’t clear. Because RMC isn’t always galvanized steel. But all rigid galvanized steel conduit is RMC.
Where should you use GRC? Use indoors in almost all locations, given its sturdiness. In almost all industrial facilities, you’ll find GRC used inside.
GRC is also a great option for outdoor use above grade. But I wouldn’t use it underground or in heavily corrosive areas. I’ve found even zinc-coated galvanized RMC doesn’t provide sufficient protection in certain areas.
Important Note: Intermediate Metal Conduit (IMC) has the same outer diameter as RMC. IMC’s wall thickness is less than RMC though. This makes IMC weaker, but creates greater interior space for wire pulling.
Flexible Metal Conduit (FMC)
What is FMC? It’s tubing made using helical coiling used indoors. It has strips of interlocked steel or aluminum. You can pull wire through it, and bend the tubing into position however you like. FMC is commonly called “flex.”
For outdoors, use Liquidtight Flexible Metal Conduit (LFMC). It’s designed to keep wires and cables free of liquid or moisture.
Important Note: FMC and LFMC are ideal for vibrating equipment. For example, a pump motor will have a flex connected to it, as a rigid conduit can snap.
PVC (Polyvinyl Chloride)
What is PVC? A rigid nonmetallic conduit, with the same advantages as RMC. But also, you can install it in wet or corrosive environments.
PVC has the following advantages:
- Easily cuttable
It can get brittle when cold and sag when hot though.
Where should you use PVC? It’s great to use in almost every application, as it is resistant to heat, fire, and sunlight. In fact, there’s no reason to use any other conduit besides PVC Schedule 40 underground. For risers though, if there’s potential for damage, use PVC Schedule 80.
Important Note: PVC Schedule 40 and PVC Schedule 80 are very similar. Except, Schedule 80 is different in the following ways:
- Greater wall thickness
- A smaller inside diameter
- Greater weight
Electrical conduit guide wrap up
Understanding the application of different conduit types is essential for every electrical project. It’s the only way to ensure a smooth install and future easy maintenance.
Which conduit type do you use most often? What causes you the most confusion when it comes to conduit selection?
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Koosha started Engineer Calcs in 2020 to help people better understand the engineering and construction industry, and to discuss various science and engineering-related topics to make people think. He has been working in the engineering and tech industry in California for over 15 years now and is a licensed professional electrical engineer, and also has various entrepreneurial pursuits.
Koosha has an extensive background in the design and specification of electrical systems with areas of expertise including power generation, transmission, distribution, instrumentation and controls, and water distribution and pumping as well as alternative energy (wind, solar, geothermal, and storage).
Koosha is most interested in engineering innovations, the cosmos, our history and future, sports, and fitness.