Daniel sent us this one — he wants to talk about conduits. Not the glamorous stuff, but the actual pipes and pathways that carry Ethernet and fiber through a building. He's asking three things: how to run cable between rooms using existing conduits or by creating new ones, what you can do yourself versus what needs a licensed pro, and how to find and inspect the conduits you've already got. It's the kind of question that sounds simple until you're staring at a wall with a fish tape in your hand.
It's the exact right question to ask before you start drilling holes. Most people skip straight to "which cable should I buy" without ever asking how the cable gets from point A to point B. The conduit is the highway system. Get that wrong and you're buying the fastest car in the world to drive on dirt roads.
The highway metaphor.
I'm a donkey, Corn. Infrastructure is my love language.
So where do we start? Let's say someone's in an apartment or a house, they want to run Ethernet from where the fiber comes in to a back room that's basically a Faraday cage made of plaster and bad Wi-Fi karma. What's step one?
Step one is figuring out what's already in the walls. Most buildings constructed in the last thirty or forty years in North America and much of Europe have some conduit already in place — but what kind, where it goes, and whether it's usable is a completely different question. In a house, you're typically looking at either electrical conduit, which you cannot and should not share with data cable, or what's called smurf tube — that blue or orange flexible plastic tubing that builders sometimes run for low-voltage stuff like coax or telephone.
That's what the industry calls it. It's officially called ENT, electrical nonmetallic tubing, but it's blue and flexible and everyone calls it smurf tube. If you've got that already running between rooms, you're in good shape. The question is whether it's empty or already packed with cables from the cable company.
How do you find out what you've got without tearing open drywall?
Couple of ways. First, pull off a wall plate — like a coaxial outlet or a blank plate — and shine a flashlight in there. You're looking for the edge of a tube around the cable, not just a cable disappearing into a hole in the stud. If you see plastic tubing, that's conduit. If you just see cable going into a hole with some spray foam around it, that's a direct run and you've got no conduit to work with.
You're looking for a sleeve, essentially. A tube the cable sits inside.
And if you find one, the next question is where does it go. The low-tech method is a tone and probe kit — you clip a tone generator onto the cable at one end, then walk around with a wand that beeps when it's near the other end. Costs about thirty to fifty dollars. It won't tell you the exact path through the wall, but it'll tell you which outlet on the other side of the room it terminates at.
That's the optimistic scenario. What's the realistic scenario for most people?
The realistic scenario is you pull off the wall plate and there's no conduit at all. Just cable stapled to studs inside the wall cavity. In that case, if you want to add Ethernet, you're either cutting drywall and installing conduit yourself, or you're looking at surface-mount raceway — which is basically conduit that sits on top of the wall instead of inside it.
The landlord special.
I prefer to call it industrial chic, but yes. And honestly, surface raceway has gotten a lot better looking than it used to be. Wiremold and Legrand both make profiles that are surprisingly low-profile and paintable. In a rental, it's often the only real option unless your landlord is unusually generous about you cutting holes.
Let's talk about the DIY versus pro line, because I think this is where people get themselves into trouble. What can an average competent person actually do, and what's the point where you should really call someone?
The line is surprisingly clear in most jurisdictions, and it's not about skill — it's about code and insurance. In the United States, the National Electrical Code draws a hard distinction between low-voltage data cabling and line-voltage electrical work. Running Ethernet, coax, or fiber is low-voltage. You generally don't need an electrician's license to do it yourself in your own home. But — and this is a big but — the moment you're putting holes through fire-rated walls or floors, you've crossed into territory where building code matters and your work needs to maintain the fire rating.
Punching a hole between two rooms on the same floor is one thing. Running a cable from the basement to the attic through multiple floors is another.
Multi-floor vertical runs are where I'd strongly recommend bringing in a low-voltage contractor or a structured cabling pro. Not necessarily an electrician — electricians often don't specialize in data cable and I've seen some truly creative interpretations of Ethernet termination from electricians who treat Cat6 like it's Romex.
That's generous.
I've seen electricians strip back six inches of twist on a Cat6 termination because "that's how you do it with power wire." The twist is the whole game with Ethernet. You undo the twist, you undo the noise rejection.
The category of "things you can DIY" includes what? Running cable through existing smurf tube, installing surface raceway, fishing cable through an unfinished basement or attic, and terminating your own jacks?
Yes, with some caveats. Terminating Ethernet jacks is absolutely DIY-able but it requires a punch-down tool and a bit of practice. Buy a cheap cable tester — twenty bucks on Amazon — and test every single run before you close up the wall. I cannot emphasize this enough. Test before you close. Nothing worse than mudding and painting drywall only to find pin seven didn't connect and your gigabit link is negotiating at a hundred megabits.
There's a special kind of despair in that moment. The freshly painted wall, the new baseboard, and then the little link light is amber instead of green.
You know it's pin seven. You just know.
What about fiber? That feels like a different beast entirely.
Fiber is simultaneously more intimidating and, in some ways, more forgiving than copper Ethernet. The intimidation factor is real — you're dealing with glass strands thinner than a human hair, and if you break one inside a wall you're not splicing it back together with a crimp tool. But the forgiving part is that fiber doesn't care about electrical interference at all. You can run it right alongside power lines, which you absolutely cannot do with copper Ethernet. NEC code requires separation between data and power — typically two inches minimum, and more if you're running parallel for long distances.
Fiber lets you cheat on the routing constraints.
And for inter-room runs where you're worried about ground loops or lightning — like running a cable to a detached garage or between buildings — fiber is the correct answer. It's electrically isolating. A lightning strike near your copper Ethernet run can fry equipment on both ends. Fiber doesn't conduct.
Terminating it yourself requires tools that most people don't own.
Field-terminating fiber requires a cleaver, a polishing puck, epoxy or mechanical splice connectors, and ideally a visual fault locator to check your work. The tool kit is a few hundred dollars minimum. For most home users, the smart move is to buy pre-terminated fiber at the exact length you need and just pull it through. Pre-terminated cables come with the connectors already factory-installed and polished. You just need to protect the ends while you're pulling.
The rule of thumb is: pre-terminated fiber for DIY, field termination for pros.
That's the rule. And when you're pulling pre-terminated fiber through conduit, wrap the connector ends in plastic and tape them up into a smooth bullet shape. The last thing you want is a connector snagging on a bend and snapping off inside the conduit. That's a "cut open the wall" level of bad day.
Let's go back to finding existing conduits, because I think there's a inspection strategy here that most people don't know about. You mentioned pulling wall plates.
If you have an unfinished basement or an accessible attic, go look. In a house, conduits often run vertically through interior walls from the basement to the attic. You'll see them as plastic or metal pipes coming up through the top plate of a wall in the attic, or going down through the sill plate in the basement. If you see empty ones, that's gold. Those were probably put in during construction for future use.
If you don't see any?
Then you're either installing new conduit, which means opening walls, or you're using alternative pathways. One pathway people overlook is cold air returns. In many houses, the ductwork for the HVAC return uses the cavity between studs, not a sealed metal duct. You can sometimes fish cable through those cavities from the basement to the upper floors. You need plenum-rated cable if you're doing that — plenum cable has a fire-resistant jacket that doesn't emit toxic smoke when it burns. Required by code inside air-handling spaces.
That's the cable with the stiffer jacket and the higher price tag.
Worth every penny when it's the difference between your house filling with hydrochloric acid smoke during a fire or not. Don't cheap out on plenum rating when you need it.
What about conduits in apartment buildings? That's a whole different regulatory environment.
In a multi-unit building, the riser — the vertical shaft that carries cables between floors — is almost certainly off-limits to residents. That's building infrastructure, and in many places it's regulated by fire code and managed by the building owner or the telecom provider. You can't just open a riser closet and start pulling cable. In some buildings, you're not even allowed to run your own cable through common areas at all.
For an apartment dweller, the realistic scope of DIY is within the unit itself.
From where the service enters your unit — often a telecom panel in a closet — to the rooms you want to connect. And within that scope, surface raceway and existing smurf tube are your friends. If your apartment was built in the last decade or so, there's a decent chance it has structured wiring already — a central panel with coax and maybe Cat5e runs to each room. Cat5e can do gigabit up to a hundred meters, so if that's what you've got, you might not even need to run new cable. Just re-terminate the existing runs with proper RJ45 jacks and you're done.
People assume they need Cat6 or Cat6a or Cat7 or whatever the marketing department is pushing this quarter. Cat5e is genuinely capable.
Cat5e will do two-point-five gigabit up to a hundred meters, and five gigabit at shorter distances, with the right equipment. The IEEE eight-oh-two-point-three-bz standard, ratified back in twenty-sixteen, made that possible. Most people don't need more than gigabit anyway. If you're just streaming video and browsing the web, gigabit is overkill. The thing that actually matters is latency and packet loss, not raw throughput.
The "my speed test number is bigger" trap.
The number of people buying multi-gig internet plans and then connecting over Wi-Fi on the other side of the house is a quiet tragedy of our time.
The bandwidth equivalent of buying a sports car to drive to the mailbox.
But we're getting off track.
So let's say someone's done the inspection, they've found either existing conduit or a viable path, and they're ready to pull cable. Walk me through the actual pulling process. What tools do they need?
The essential tool is a fish tape — a long, flat, spring-steel coil that you push through the conduit from one end to the other. You attach the cable to the end of the fish tape with electrical tape, making a smooth tapered connection, and then pull it back through. For shorter runs through open walls, you can use fiberglass push rods instead — they're more flexible and less likely to snag on insulation. For conduit that already has a cable in it, you use the existing cable as a pull string. Tie your new cable to the old one with a pulling grip and pull.
If the conduit is empty but has bends?
Bends are the enemy. Every bend increases friction. The National Electrical Code limits conduit to three hundred sixty degrees of total bend between pull points — that's four ninety-degree bends. More than that and you're probably not getting anything through without lubricant. Yes, cable pulling lubricant exists. It's a water-based gel that dries to a non-conductive powder. Looks like hand sanitizer, feels like regret, works like magic.
"Feels like regret.
You'll understand when you've got it all over your hands and you're trying to grip a fish tape.
I'll take your word for it. What about conduit size? How do you know if a cable will actually fit?
There's a fill ratio. For data cable, the rule of thumb is the cable's cross-sectional area should not exceed forty percent of the conduit's internal cross-sectional area. For a single cable in a conduit, you can go higher, but if you're pulling multiple cables, stick to forty percent. There are online calculators for this — you input the cable diameter and the conduit size, and it tells you if you're within spec. For reference, a half-inch smurf tube can comfortably fit two Cat6 cables. Three-quarter-inch can fit four or five. One-inch can handle a bundle.
Fiber is thinner, so you can fit more?
A single duplex fiber cable is about three millimeters in diameter. You can fit a dozen of them in a half-inch conduit with room to spare. This is one of the reasons fiber is appealing for future-proofing — you can pull a bundle of fiber through a small conduit and have capacity for decades.
Let's talk about new conduit installation, because that's the part where most people's confidence collapses. If you don't have existing conduit and you need to create a path, what's the process?
The process is: cut holes in drywall, drill holes through studs, install conduit or just pull cable through the holes, and then patch the drywall. The drilling part is where you need to be careful. You're drilling through the center of each stud — not the edge, because you need to maintain at least one and a quarter inches from the edge of the stud to protect the cable from drywall screws. If you can't maintain that distance, you need a metal nail plate to protect the cable.
This is where the DIY-versus-pro line gets blurry.
Cutting and patching drywall is absolutely a DIY skill, but it's also the skill that separates a finished project that looks professional from one that looks like someone punched a hole and smeared putty over it. If you've never done drywall finishing before, your first attempt will look bad. That's just a fact. It takes practice to feather out joint compound so the seam disappears.
The honest advice is: pull the cable yourself, hire a drywaller to close it up.
That's what I'd do. Or if you're in an unfinished space — basement with exposed joists, attic with open access — you skip the drywall problem entirely. Run the conduit along the joists, strap it down every four feet or so as required by code, and you're done.
What type of conduit should someone use for new interior runs?
For interior residential, smurf tube — ENT — is the standard. It's flexible, it's inexpensive, and it's easy to work with. You can buy it in hundred-foot coils at any home improvement store. For exposed runs in a basement or garage, you might use EMT — electrical metallic tubing — which is rigid metal conduit. It looks cleaner and provides physical protection. But EMT requires a pipe cutter, a deburring tool, and connectors. More tools, more skill.
For exterior runs? Say someone wants to run Ethernet to a shed or a backyard office.
Exterior is a whole different animal. You need outdoor-rated cable — UV-resistant jacket, gel-filled for water blocking if it's going underground — and the conduit needs to be rated for wet locations. PVC conduit, schedule forty or schedule eighty, is standard for underground runs. And you need to bury it at the proper depth — typically eighteen to twenty-four inches for direct-burial cable, less if it's in conduit. Check local code. And use fiber for any run between buildings with separate electrical services. Ground potential difference is a real thing and it will destroy equipment.
The voice of experience?
Let's just say I once saw a network switch with its Ethernet ports literally blown out the back. Lightning strike a hundred feet away, induced current on an underground copper run, and the switch became a very brief but very bright light.
That's how you learned about fiber.
That's how I learned about fiber.
Okay, so we've covered finding conduits, pulling cable, and installing new paths. Let's talk about the inspection side more thoroughly. What should someone look for when they're evaluating an existing conduit system — say in a building they're thinking of buying or renting?
This is where I get on my soapbox about telecommunications infrastructure during property inspections. When you walk through a property, you check the plumbing, you check the electrical panel, you check the roof. Nobody checks the data pathways. And in twenty-twenty-six, the data pathways are as essential as any of those other systems.
What's the checklist?
First, find the demarcation point — where the outside service enters the building. In a house, it's usually a gray box on the outside wall, often near the electrical meter. Open it up if you can. Look for a conduit running from that box into the house. If it's just a hole with some silicone caulk, that's not great but it's common.
That's the telco term?
Demarc, for short. It's the legal boundary between the provider's responsibility and yours. Everything on the house side of the demarc is your problem.
Demarc, then inside.
Second, find where the interior wiring converges. In newer homes, there's often a structured wiring panel — a white metal box recessed into a wall, usually in a closet or the basement. Open it up. You're looking for: one, conduits or cables running out to various rooms; two, a power outlet inside or near the panel for powered equipment; three, labeling. If the cables are labeled with their destinations, someone cared. If it's a rat's nest of unlabeled coax, nobody cared.
The label test. It really does tell you everything about how the building was constructed.
A builder who labels cables is a builder who thought about the person who'd be living there. Third thing to check: pull a few wall plates in key rooms and look at what's behind them. Is there conduit? Is there a pull string left in the conduit for future use? A pull string is a piece of nylon cord left inside empty conduit specifically so you can pull cable through later. It's a sign that someone future-proofed the installation.
If there's no pull string, how do you get one in?
You use the fish tape to pull a pull string through first, then use the pull string to pull the actual cable. Or you use a vacuum cleaner and a plastic bag. Tie a plastic grocery bag to a piece of string, stuff it in one end of the conduit, and suck it through with a shop vac at the other end. It's absurd but it works incredibly well.
That's the kind of tip that sounds like a prank but is actually genius.
It's one of my favorites. The first time I saw someone do it, I thought they were messing with me. Then the string shot out the other end like a party favor.
What about inspecting conduit for damage? Cracks, blockages, that sort of thing?
For rigid conduit, you can shine a bright flashlight in one end and look from the other. If you see light, it's clear. For flexible conduit with bends, you won't see light, so you use the fish tape test — does it go through smoothly or does it hit something solid? If it hits something, don't force it. The blockage could be a kink in the conduit, a screw that pierced it during drywall installation, or a nest of some kind. Yes, mice love conduit.
Of course they do.
If you suspect a blockage, an inspection camera — a borescope — is the tool. You can get a USB borescope that plugs into your phone for about forty dollars. Feed it in and see what you're dealing with. It's also useful for finding conduit paths in walls without opening them up.
The forty-dollar borescope pays for itself the first time you don't cut a hole in the wrong place.
Ten times over. Every homeowner should own one. They're also great for finding things you dropped behind furniture without moving the furniture. But that's a different podcast.
The "things behind furniture" podcast. We'll pitch it. Let's talk about what you can and can't run through conduit together. I know power and data need separation.
The rule is: low-voltage data cables can share conduit with other low-voltage data cables. Ethernet with coax with fiber with telephone — all fine. What you cannot do is mix power and data in the same conduit. It's not just about interference — it's a safety issue. If a power cable's insulation fails and energizes the conduit, every data cable in there becomes a shock hazard. The NEC prohibits it explicitly.
What about different types of data cable? Can you mix copper Ethernet and fiber in the same conduit?
Fiber is non-conductive — it's glass and plastic. It doesn't care what it's next to. You can bundle fiber with anything. That's another point in fiber's favor for future-proofing. Pull fiber alongside your existing copper and you've got an upgrade path that doesn't require opening walls again.
What about HDMI or other A/V cables?
HDMI can share conduit with Ethernet, but there's a practical problem: HDMI connectors are huge. You're not pulling a terminated HDMI cable through a half-inch conduit. You'd need to pull the cable and then terminate it in the wall, which is not something most people can do with HDMI. For A/V distribution, the modern approach is HDMI over Ethernet — use baluns on both ends and run Cat6. Or just use HDBaseT, which is the standard for this.
The advice is: don't try to pull HDMI through conduit. Convert to Ethernet and pull that instead.
And honestly, for most residential A/V these days, you don't even need dedicated cables. Streaming boxes at each TV, content over Wi-Fi or Ethernet. The era of centralized A/V matrix switches with dedicated HDMI runs to every room is fading.
Another thing people might not think about: what about the conduit itself as a grounding path? Does metal conduit need to be grounded?
Yes, and this is one of those code details that DIYers often miss. Metal conduit — EMT or rigid metal conduit — must be grounded. It's typically grounded through the connectors and the metal boxes it attaches to, which are themselves grounded. Plastic conduit like ENT or PVC doesn't need grounding because it's non-conductive. This is another reason ENT is popular for residential data — one less thing to worry about.
What about firestopping? When you run conduit between floors, you're creating a path for fire to spread.
Any penetration through a fire-rated assembly — a floor, a firewall between units in a multi-family building — needs to be firestopped. There are specific products for this: intumescent caulk, firestop collars, mineral wool packing. The product expands when heated and seals the opening. This is not optional, and it's one of the areas where I'd say, if you're not confident you know what you're doing, hire someone. Getting firestopping wrong doesn't just fail an inspection — it creates a real safety hazard.
The firestopping is arguably the most important part of a multi-floor install.
The cable might work or it might not — you'll find out and fix it. The firestopping either works or it doesn't — and you find out when it's far too late.
That's a sobering thought to end a segment on. Let's shift to something more optimistic: what does a really well-done conduit installation look like? The gold standard.
A gold-standard residential conduit installation has a few characteristics. One, a central distribution point — a structured wiring panel or a small wall-mount rack — with conduit running from that panel to every room that might ever need data. Two, each conduit has a pull string left in it for future use. Three, the conduits are labeled at both ends with their destinations. Four, the panel has power and ventilation. Five, there's at least one spare conduit running from the basement to the attic for future vertical expansion. And six, the outdoor demarc conduit is oversized — at least one inch — so you can pull whatever the provider brings next.
That last point is interesting. Oversizing the conduit from the outside.
It's one of the cheapest forms of future-proofing. The difference in material cost between half-inch conduit and one-inch conduit is maybe twenty cents a foot. The difference in labor is zero — you're digging the same trench, drilling the same hole. But when the telco shows up in five years with a new type of fiber that has a thicker jacket or a pre-terminated connector that doesn't fit through half-inch, you're either ready or you're not.
Twenty cents a foot for infinite future flexibility.
It's the best return on investment in the entire construction budget.
What about conduit in older buildings? Pre-war construction, plaster walls, no smurf tube, probably knob-and-tube wiring you don't want to touch.
Older buildings are the hardest case, and they're also where conduit is most valuable — because you're not fishing cable through walls filled with who-knows-what. In a pre-war building with plaster and lath walls, fishing cable is a nightmare. The lath catches the fish tape, the plaster crumbles, and the wall cavities are often blocked by horizontal firestops that you can't see. In those cases, surface raceway becomes attractive, or you accept that you're going to have a professional do it and deal with the plaster repair.
The "accept your limitations" lesson.
Sometimes the smartest DIY decision is knowing when not to.
To pull all this together — if someone's listening and they want to run cable between rooms this weekend, what's the sixty-second decision tree?
Step one: pull a wall plate and look for conduit. If you find smurf tube and it's empty or has room, buy a fish tape and pull your cable. Step two: if there's no conduit but you have an unfinished basement or attic, run the cable through those spaces and drill up or down into the walls. Still DIY, but more work. Step three: if you have finished walls and no conduit and no basement or attic access, consider surface raceway or hire a pro to fish the walls. Step four: if you're going between floors through fire-rated assemblies, hire a pro or at minimum research firestopping requirements thoroughly. Step five: if you're running between buildings, use fiber.
That's clean. And the tools someone should own before starting?
Fish tape, a cable tester, a punch-down tool, a drywall saw, a drill with a long flexible bit for drilling through studs, a stud finder, a tone and probe kit, and a headlamp. Because you will be in dark spaces. Probably uncomfortable ones.
The headlamp is underrated advice.
Every DIY project is a headlamp project if you're doing it right.
One last thing I want to touch on: the code and permitting question. When does running some Ethernet trigger a permit requirement?
Varies by jurisdiction, but generally: low-voltage data cabling in a single-family home does not require a permit if you're doing it yourself. If you're hiring a contractor, they need a low-voltage license in most states. If you're in a multi-unit building, the building may have its own rules that are stricter than the municipal code. And if you're adding new conduit that penetrates fire-rated assemblies, you may need a permit and an inspection regardless. Check with your local building department. It's a phone call that takes five minutes and can save you a lot of trouble.
"It's a phone call that takes five minutes" is probably the most adult thing you've said all episode.
I contain multitudes.
Now: Hilbert's daily fun fact.
Hilbert: The platypus is one of the only mammals capable of electrolocation, using receptors in its bill to detect the tiny electrical fields generated by the muscle contractions of its prey. This sensory system has no known evolutionary intermediate forms in the fossil record and appears fully formed in the earliest platypus ancestors, making it a surviving artifact of a sensory strategy that evolved in complete isolation on a single branch of the mammalian tree.
Platypuses are basically nature's tone and probe kit.
Don't forget the venom.
This has been My Weird Prompts. Thanks to our producer Hilbert Flumingtop. If you found this useful, leave us a review wherever you listen — it helps. We'll be back next week with something completely different.
Probably not about conduits.
Almost certainly not about conduits.
