You’ve seen them. Those gray PVC pipes running along the side of a garage or the shiny metallic tubes snaking across a basement ceiling. Most people just call them "pipes," but in the world of electrical work, they go by a more specific name: conduit. It’s one of those things that seems boring until you actually need to install a new outdoor outlet or wire up a workshop. Then, suddenly, the difference between EMT and rigid metal becomes the most important thing in your weekend project.
What is a conduit, exactly?
Think of it as a dedicated highway system for your wires. It isn't just a sleeve; it’s a protective environment designed to keep electricity where it belongs and keep the outside world—like moisture, shovels, or hungry rodents—away from sensitive copper. While "conduit" can technically refer to anything that carries a fluid or gas, when we talk about it in a home or industrial setting, we’re almost always talking about electrical safety.
Why You Can’t Just Run Bare Wires Everywhere
In a perfect world, wires would just hang out behind your drywall and never get touched. But the real world is messy.
If you’re running power to a detached shed, you can’t just bury a standard Romex cable (the white or yellow stuff you see in your attic) six inches under the dirt. The ground is acidic. It's wet. Also, you might eventually decide to plant some petunias right where that wire lives, and a single thrust of a spade would result in a very unpleasant surprise.
This is where the concept of a "raceway" comes in. The National Electrical Code (NEC)—specifically NFPA 70—is pretty obsessed with these. They don’t just want the wire to be safe; they want it to be "accessible." If a wire inside a conduit fails, you can theoretically pull it out and fish a new one through without tearing down your walls. Try doing that with a cable stapled to a stud.
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The Different Flavors of Conduit (And When to Use Them)
Not all conduit is created equal. If you walk into a Home Depot or Lowe's, you’ll see a dizzying array of materials. Honestly, picking the wrong one is a classic DIY mistake that can lead to failed inspections or, worse, a fire hazard.
EMT: The Shiny Stuff
Electrical Metallic Tubing, or EMT, is the thin-walled galvanized steel tubing you see in most commercial buildings. It’s lightweight and easy to bend with a tool called a hickey (yes, that’s the real name). It isn't threaded. Instead, you use setscrew or compression fittings to join pieces together. Because it’s thin, you shouldn't use it where it might get crushed by a forklift, but for a home garage? It’s perfect.
PVC: The Plastic Standard
Rigid Polyvinyl Chloride (PVC) is the go-to for underground burials and wet locations. It’s cheap. It’s waterproof if you glue the joints correctly. However, it has a massive downside: it expands and contracts like crazy when the temperature changes. If you run a long stretch of PVC on an outdoor wall without "expansion joints," the sun will eventually warp it until it pops right off the brackets.
Flexible Metal Conduit (FMC)
You’ve probably heard people call this "Greenfield." It looks like a metallic snake. You use this when you need to connect something that vibrates—like an air conditioner compressor or a furnace motor. If you used a rigid pipe there, the vibration would eventually crack the connections. "Flex" absorbs that movement.
The "Fill Capacity" Trap
Here is something most people screw up: you can’t just jam as many wires as possible into a conduit.
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Heat is the enemy. When electricity flows through a wire, it generates heat. If you have ten wires packed tightly in a small tube, that heat has nowhere to go. The insulation can melt. This leads to what electricians call a "short circuit" and what firefighters call "a Tuesday."
The NEC has very specific tables—usually based on a 40% fill ratio—that dictate how many conductors of a certain gauge can fit in, say, a 1/2-inch or 3/4-inch pipe. If you’re pulling three 12-gauge wires through a 1/2-inch EMT, you’re fine. If you try to shove ten in there? You’re asking for a disaster.
Grounding: The Conduit Is Part of the Circuit
In many jurisdictions, if you use metal conduit like EMT or IMC (Intermediate Metal Conduit), the pipe itself acts as your ground path. This is a bit of a polarizing topic among old-school sparkies.
Some guys trust the pipe. They argue that as long as every coupling is tight, you don't need a separate green ground wire. Others—usually the ones who have seen a loose coupling spark during a fault—insist on "pulling a green." Personally? Always pull the ground wire. It’s cheap insurance. If a rust spot or a loose screw breaks the continuity of your metal pipe, and a hot wire hits the casing, the whole conduit becomes "live." You touch the pipe, you become the path to ground. Not fun.
The Art of the Bend
You haven't lived until you've tried to bend a "saddle" or a "back-to-back 90" in a piece of steel pipe. It’s more math than most people expect. You have to account for "shrink"—the distance the pipe loses as it curves—and "take-up."
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Professional electricians spend years perfecting this. If you’re doing it yourself, buy extra pipe. You will kink it. You will bend it backwards. You will probably throw a piece across the yard in frustration. But once you get a perfectly level run of conduit across a wall, it’s strangely satisfying. It looks intentional. It looks professional.
Critical Safety Checklist for Your Next Project
Before you start hacking away at some tubing, keep these hard-and-fast rules in mind. They aren't suggestions; they are the difference between a job that lasts 40 years and one that fails in four months.
- Deburr your edges. When you cut metal conduit with a hacksaw or a pipe cutter, the inside edge becomes razor-sharp. If you don't use a reamer or a round file to smooth that out, the sharp edge will slice the insulation off your wires as you pull them through. Boom. Instant short.
- Support it properly. Don't let your conduit sag. The code generally requires a strap within three feet of every box and then every ten feet after that. If it's heavy rigid pipe, those rules get even tighter.
- Watch your "bends." You cannot have more than 360 degrees of total bends between "pull points" (boxes). That’s four 90-degree turns. If you do five, the friction will be so high you’ll never get the wire through, or you'll tear the jacket trying.
- Use the right wire. You cannot pull "Romex" (NM-B) through outdoor conduit. The paper wrapping inside the cable wicks up moisture and rots. You need THWN or THHN wire, which is rated for "wet" or "damp" locations inside a raceway.
Taking Action: Mapping Your Path
If you are planning to add power to a new area, start by measuring your run and counting your turns. If your total bends exceed 360 degrees, you must install a "conduit body" or a junction box to act as a midway pulling point.
Check your local codes first. Some cities (looking at you, Chicago) require conduit for everything, even inside residential walls, while most of the country allows flexible plastic-sheathed cable for interior work. Knowing the difference saves you from a massive headache during a home sale inspection later.
Buy a dedicated conduit bender rather than trying to use a fence post or a tree limb. The $40 investment will save you $100 in wasted material and a lot of swearing. Start with your boxes—mount them first—then run the pipe between them. It’s much easier to fit the pipe to the boxes than the other way around.
Once the pipe is up and secure, use a "fish tape"—a long, flexible steel ribbon—to pull your wires through. If the run is long or has lots of turns, use "wire pulling lubricant." It looks like snot, but it makes the wires slide through like they’re on ice.
Done correctly, a conduit system is basically a permanent upgrade to your home's infrastructure. It’s the difference between a "handyman special" and a system that actually meets the rigorous standards of modern electrical engineering.