Planning the Route First
Routing cable through finished walls is significantly harder than it looks, and the difficulty depends almost entirely on what is in the wall — insulation, fire blocks, noggins, and existing wiring all create obstacles that are invisible until you are committed. Spend time planning before drilling anything. Walk both floors if running between levels. Tap walls to find studs and note their spacing. Identify where the cable needs to start and end, and think through every horizontal and vertical transition.
Jacket rating matters for in-wall use: CMR (riser-rated) cable is the minimum for in-wall runs. CMP (plenum-rated) is required in air-handling spaces such as drop ceilings used as HVAC return plenums. Do not use CL2/CL3 rated cable (designed for speaker wire) or unrated cable inside walls — it does not meet fire code for building wiring.
Tools Needed
- Drill with long bit: a flexible drill shaft with a 3/4" or 1" spade bit for drilling through top and bottom plates horizontally. A right-angle drill attachment helps in tight stud bays.
- Fish tape or fish sticks: a rigid fish tape (steel or fiberglass) fed from one opening to retrieve the cable at the other. Fish sticks are shorter rigid sections that link together, useful in insulated walls where a tape coils back on itself.
- Stud finder: to locate studs and avoid them (or drill through their centers at 1.25" minimum from the face to avoid nail plate requirements).
- Drywall saw: for cutting wall jack openings and any access holes needed for fishing.
- Glow rods: fiberglass rods that connect together and illuminate at the tip — the light shows through drywall to help locate the rod's position in a dark wall cavity.
- Magnetic stud finder or rare-earth magnet: useful for locating drill holes behind drywall by following a steel fish tape magnetically.
Common Routing Paths
| Route | Method | Common Obstacle |
|---|---|---|
| Same-floor, adjacent rooms | Drill through stud between rooms; fish horizontally | Fire blocks (horizontal 2×4s mid-wall height in some construction) |
| Same-floor, non-adjacent rooms | Run through attic or crawlspace; drop into each wall cavity | Insulation, HVAC ducts blocking attic path |
| Between floors (up) | Up through floor plate into wall cavity; fish up to next level | Top plate blocking the cavity at the ceiling level |
| Between floors (down) | Down through ceiling into wall cavity from attic or upper floor | Fire blocks, insulation, junction boxes in the path |
| Basement to first floor | Up through sill plate into wall cavity | Insulation in exterior walls; finished basement ceilings |
Step-by-Step Process
- Mark both endpoints: Identify the wall jack location and the destination (patch panel, equipment room). Cut the jack opening first so you have a hole to work from.
- Access the top or bottom plate: Most runs require drilling through a top plate (going up into the attic) or a bottom plate (going down into the basement or crawlspace). Drill a 3/4" hole centered in the plate, at least 1.25" from the face of the stud to avoid needing a nail plate.
- Feed the fish tape: From the attic or crawlspace, push the fish tape down into the wall cavity toward the jack opening. Have a helper at the jack opening with a flashlight to spot the tape and grab it with needle-nose pliers or a wire hook.
- Attach and pull cable: Tape the cable to the fish tape hook with electrical tape, fold the cable end back on itself and tape it smooth so it does not catch on obstructions. Pull the fish tape back through from the other end, drawing the cable with it. Leave 12–18 inches of slack at each end.
- Secure and protect: Where the cable passes through a drilled plate, install a plastic bushing to protect the jacket from the rough wood edge. Do not staple cable tighter than the cable's outer diameter — staples that crush the jacket deform the pair geometry and degrade performance.
- Test before closing: Plug in a wire map tester before mounting wall plates or patching drywall. Finding a fault after the wall is closed is much more expensive than finding it before.
Frequently Asked Questions
How do I get past a fire block inside the wall?
Fire blocks (horizontal fire stops) are 2×4s installed horizontally within a wall cavity, typically mid-height, to slow vertical fire spread. They are common in platform-frame construction in some regions. When you hit a fire block, you have three options: drill through it (requires an offset drill or right-angle attachment to reach past the drywall), access it from behind if there is an adjacent open cavity or closet, or route around it through the attic or crawlspace instead. Use a glow rod to probe the cavity before drilling — you can often feel whether something is blocking the path before committing to a hole.
Is it safe to run Ethernet near electrical wiring inside walls?
Yes, with some separation. Unshielded Ethernet is susceptible to interference from AC power wiring, particularly at close parallel runs. The NEC (National Electrical Code) and TIA-568 both recommend at least 2 inches (50 mm) of separation for parallel runs near 120V wiring, and more separation near higher-voltage circuits or fluorescent lighting ballasts. Crossing electrical wiring at 90 degrees (perpendicular) is fine and introduces negligible interference. Do not bundle Ethernet with power cables and never run them in the same conduit. Keep separation in mind when planning the route — routing through a different stud bay than the power wiring is the simplest solution.
Can I use a coat hanger or homemade tool instead of a proper fish tape?
For very short, unobstructed runs (fishing through a single stud bay, a few feet straight down), improvised stiff wire can work. For anything longer or with corners, a proper fish tape or fish sticks are worth the cost. Fish tapes are designed not to kink, have hooks that hold cable reliably, and come in long enough lengths for real building runs. A coat hanger kinks immediately in a wall cavity and cannot navigate the 90-degree turn from the top plate into the wall cavity. A 25-foot fiberglass fish tape costs about $20 and handles almost every residential run.