Before you can install and inspect electrical conduits, you need to know the basics. So, I’ve made this beginner’s electrical conduit guide with added tips.
You’ll learn about the main types of electrical conduit and their applications. This will allow you to complete most jobs that involve electrical infrastructure work.
In my discussion, 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.
Each conduit type has a different application in electrical installations. By choosing the correct type, you’ll have the following benefits:
- Easy installations
- Less maintenance
- Simple repairs
Before we go over each conduit type though, let’s first discuss some general conduit tips and tricks. This will help familiarize you with conduits and various requirements.
If you like, you can scroll all the way down past the 10 tips to go straight to the conduit type explanations.
Important Note: for any electrical work, use the latest National Electrical Code (NEC). It’s the best source of information for how to install electrical infrastructure. Also, it’s your blueprint to remain code compliant.
Then, call your local building department to check for any locally enforced codes.
General conduit tips for every project
Use these tips with the NEC requirements to properly install conduits. These are tips I’ve gathered over the years working on different engineering projects.
You can apply these tips to any at-home projects as well.
#1 Draw up a schematic diagram
Before you pick up any tools, draw yourself a conduit schematic plan. The benefits include:
- 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: if you’re installing underground conduit runs, get existing area plan drawings.
Call your local utility company and they’ll tell you where any buried pipes are.
This way, you don’t accidentally hit a gas line.
#2 Conduit sizing
Size your conduit per the number of wires you’ll pull through it. As your guideline, use NEC Chapter 9, Table 1:
|Number of Conductors in Conduit||Maximum Fill Allowance|
Then use our two following sizing tools to quickly size your conduit:
Important Note: for long conduit runs, go up one size. This will makes installation and maintenance easier. Especially if you have a couple of 90 degree bends in your conduit run.
Also, keep your minimum conduit size to 3/4-inches. This will make wire pulling much easier.
#3 Conduit bends
NEC 358.26 limits the total number of bends to 360° in total. But I suggest limiting the number of directional changes to no more than 270° in any run between pull points.
This makes installation and future maintenance much easier. Especially when you pull large conductors.
So, when a single conduit run includes more than 270° in bends, install a pull box.
Important Note: 360° in total bends is allowable by the NEC.
Still, avoid bends and offsets where possible though. But when necessary, make your turns using fittings. Then as a last resort, make bends with an approved hickey or conduit bending machine.
#4 Conduit Supports
Secure all conduits and fittings on exposed surfaces with clamp backs and channels or struts. The spacing of conduit supports to be as required by the National Electrical Code, but to not exceed 4 ft.
Refer to NEC 358.30.
#5 Conduit fittings
Unthreaded fittings fall into two categories:
- Gland (compression) type
- Set-screw type
Gland type is the only unthreaded fitting type you can use in wet locations.
For non-wet locations, join conduits together using thread-less set-screw couplings. The end pieces of conduits go inside either end of the couplings. You then tighten the coupling with set-screws.
In your projects though, specify only one fitting type. Otherwise, it becomes confusing on which fitting type an electrician is to use. They’ll constantly be guessing should I use this or that fitting.
The following are other common fittings you should use and why:
- Expansion fittings: use in areas where large temperature swings happen. This will limit stress damage on conduits from expansion and contraction.
- Ground fittings: use where ever you think a conduit break will happen. Whether for maintenance or repair. This fitting allows you to jumper around any discontinuities in a ground path. In other words, they allow for a continuous path to ground.
- Elbows: use when you need to change a conduit run direction by 90°.
- Drain: use if you’re installing in an area with temperature swings. In other words, places where you have condensation. So, install a drain at the lowest point of a conduit run where water may gather.
#6 Pre-bent conduits and fittings
In routing your conduit, you’ll cut, couple, and bend your conduit(s).
For example, you can bend EMT using a conduit bender. BUT, using pre-bent conduit and fittings will greatly simplify your work.
So, find parts to complete your conduit run like a puzzle. Do the least amount of self-bending to avoid possible conduit damage.
#7 Cutting and reaming conduits
You can cut EMT using a hacksaw.
But after cutting, be sure you “ream”, or smooth, the edges with a metal file. This is very important, as the sharp edges of the conduit can tear and damage wires you pull through.
#8 Through the wall conduit penetrations
Install conduit wall seals for all conduits penetrating walls. Then install expansion and deflection fittings where conduits cross any building expansion joints.
Also, make all roof penetrations watertight with weatherproof metal flashing caps. Use hot-dipped galvanized sheet metal for the caps.
#9 Underground and aboveground conduit installations
For the most long-lasting installations, use the following conduit types:
Underground: use nonmetallic Schedule 40 high impact polyvinyl chloride for underground conduits. Conduits to also be UL approved for direct burial or concrete encasement. This is for cables operating at 90°C.
Additionally, fittings used with PVC conduit to be PVC solvent weld type.
Keep in mind, underground conduit installations are far from easy. You need to have a background in the work to do it right.
Important Note: underground to aboveground 90° elbows to be PVC coated GRC. Riser pipes to be PVC coated GRC as well.
The importance of this I explain in underground conduit installations.
Aboveground: use rigid steel conduits for aboveground installations. The raceways need to conform to ANSI 1 C80.1.
Also, apply zinc coating to the inside and out by hot-dip galvanizing after threading.
#10 Exposed conduit raceways
Run all conduits on exposed surfaces at right angles to and/or parallel with the surrounding walls. Also, conform exposed conduit runs to the form of ceilings.
At the same time, don’t install diagonal runs. But, do provide concentric bends for parallel conduit runs.
I’d say without a doubt, installing conduits is an art.
EMT (Electrical Metallic Tubing)
What is EMT? It’s not technically a conduit, but a tubing.
You can thread EMT. But most times, 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? It’s 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 not to install it anywhere where it’s subject to physical damage. This is why EMT is more so found installed in the following places:
- Inside of walls
- In offices and corridors
In the above areas, EMT makes a much better choice than GRC. Because GRC is overkill and much more expensive. We’ll discuss GRC next.
Important Note: when possible, color code the EMT inside your building. Choose a different color for 480V, 120V, and 24V wiring. This greatly helps with maintenance work.
GRC (Galvanized Rigid Steel Conduit)
What is GRC? It’s a thick wall conduit. The conduit can have threaded ends, coupled with threaded fittings too. But also, you can have threadless fittings.
To point out, Rigid Metallic Conduit (RMC) is a generic name and GRC is a specific name.
You can buy steel, stainless steel, and aluminum RMC. But GRC is the most commonly used type.
Also, RMC is commonly called “rigid.”
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”, it’s not clear what conduit you need to use. 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. It’s sturdy and it’s not easily damaged.
This is why inside industrial facilities, you’ll mostly find GRC used.
Also, GRC is a great option for outdoor use. For example, mounted on roofs.
But I wouldn’t use it underground or in heavily corrosive areas. Unless of course, the GRC is PVC coated.
I’ve found even zinc-coated galvanized RMC doesn’t provide enough protection in some places. This is one reason I don’t install GRC underground.
Important Note: Intermediate Metal Conduit (IMC) is like RMC. It has the same outer diameter as RMC.
The wall thickness of IMC is less than RMC though. Thus, it has greater interior space for wires, but it’s less sturdy.
Flexible Metal Conduit (FMC)
What is FMC? It’s a tubing made using helical coiling. It has strips of interlocked steel or aluminum.
You can pull wire through it, and then bend the tubing into position however you like.
Also, FMC is commonly called “flex.”
Where should you use FMC? Areas where there’s limited space.
FMC is good to use for large equipment and appliances that you need to move around for repair a lot. So anytime you’ll move something frequently or swap things out, FMC is a good option.
Important Note: FMC is ideal for equipment that shakes, moves, or vibrates. It’s used in the final 6-feet or less of raceway from a rigid conduit to equipment that’s prone to vibrations.
For example, a pump motor will have a flex connected to it.
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. It has the following advantages:
- Easily cuttable
But, it can get brittle when cold and sag when hot.
It’s like a plastic plumbing pipe. So it’s installed with plastic fittings that you glue in place. This makes the conduit assemblies watertight and great for underground installations.
You can also bend PVC in a portable heater box.
Where should you use PVC? It’s great to use in almost every application, as it is resistant to heat, fire, and sunlight.
For underground installations, I see no reason to use anything other than PVC Schedule 40. Then for risers, 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
This makes Schedule 80 conduit a great choice to meet the NEC’s requirement for “protection from physical damage.” This is per NEC 352.10(F).
So, for aboveground work, where a conduit can get hit like in a garage, use Schedule 80.
Electrical conduit guide wrap up
Understanding the different types of conduits is essential in any electrical infrastructure project.
Because installing conduits can be an arduous and time-draining task. Even more so if you don’t know the many nuances of the different conduit types.
But with proper planning and conduit selection, your work becomes much easier. In fact, electrical conduit design and then installation becomes a breeze.
What do you find to be the most important in our electrical conduit guide? Which type of conduit do you use most often?
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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.