What's the easiest, code-compliant way to run Ethernet to a detached garage?

Short answer

The cleanest, most code‑friendly way to run network to a detached garage is to trench a dedicated conduit and pull a dielectric fiber optic cable between buildings. Terminate the fiber to media converters or switches with SFP ports at each end. Fiber avoids grounding/bonding issues, surge protectors, and lightning risks that come with copper Ethernet between structures. If you prefer copper, use outdoor‑rated Cat6 in its own conduit, keep required separation from power, add listed Ethernet surge protectors at both ends, and bond them to each building’s grounding electrode system.

Why fiber is the easiest way to pass code (and stay reliable)

• Fiber is non‑conductive. There’s no metallic path between buildings, so you don’t have to install primary protectors or worry about ground potential differences and lightning surges.
• Fewer code headaches. Communications rules for inter‑building metallic cables require protectors and bonding; fiber largely sidesteps that.
• Long runs and speed. Fiber handles long distances and high bandwidth with no 100 m limit like copper Ethernet.

If trenching is tough, a point‑to‑point outdoor wireless bridge is another practical route, but a physical link in conduit is usually faster, more stable, and maintenance‑free once installed.

Specs at a glance

Conduit: 3/4–1 in. PVC Sch. 40 underground; Sch. 80 where exposed
Burial depth: 18 in. cover typical (verify with local AHJ)
Separation from power in same trench: 12 in. horizontal (cross at 90°)
Pull boxes: every 150–200 ft or after >360° of bends
Ethernet copper limit: 100 m (328 ft) per run
Protector requirement: Metallic comms between buildings need listed protectors bonded to GES; fiber does not

Materials (fiber option)

• Outdoor‑rated dielectric fiber optic cable (2–6 strand). Pre‑terminated ruggedized assemblies simplify install.
• 3/4–1 in. PVC Schedule 40 conduit, sweeps, couplings, LB bodies, and Sch. 80 where exposed.
• Pull string or 1/8–1/4 in. mule tape; wire pulling lubricant.
• Two SFP media converters or network switches with SFP ports, plus matching SFP modules (e.g., 1G multimode or single‑mode).
• Weatherproof junction box or structured media panel at each end, grommets, duct seal, silicone.
• Warning tape (buried 6–12 in. above conduit).

Tools

• Trenching shovel or rental trencher; mattock.
• PVC cutter, primer and solvent cement.
• Fish tape or vacuum and foam “mouse” for pulling line.
• Tape measure, marker, utility knife.
• Personal protective equipment: gloves, eye protection, boots.

Step‑by‑step: fiber in conduit

1. Call 811 before you dig. Mark all utilities. Pick a route that avoids tree roots and heavy vehicle loads where possible.
2. Plan your pathway. Keep at least 12 in. separation from any existing power in the same trench. If you must cross power, do it at 90°.
3. Trench to 18 in. depth (or deeper if local rules require or if under a driveway). Lay 2–4 in. of sand or fine soil for a bed.
4. Dry‑fit conduit. Use long‑sweep bends (no tight 90s). Avoid more than 360° of total bend between pull points. Install LB bodies or an accessible pull box if needed.
5. Solvent‑weld the conduit. Prime and cement each joint. Transition to Sch. 80 where the conduit emerges, and protect stubs from damage.
6. Install a pull line. Use fish tape or a vacuum with a foam plug to blow/pull in mule tape. Leave extra at both ends.
7. Pull the fiber. Cap or tape ends to protect connectors if pre‑terminated. Use pulling lubricant and gentle, steady tension; respect the cable’s minimum bend radius.
8. Seal entries. Create drip loops, sleeve through the wall, and seal penetrations with duct seal or silicone to keep out moisture and pests.
9. Terminate and test. Plug SFP modules into converters/switches, connect fiber, power up, and verify link with a continuity/light source tester or network link LEDs. Label both ends.
10. Backfill. Place warning tape 6–12 in. above conduit before final backfill.

Time/cost: A 60–120 ft run typically takes a weekend for a DIYer. Expect roughly $150–300 for conduit and consumables, $120–250 for pre‑terminated fiber, and $60–250 per end for SFPs/media converters (or use switches you already own with SFP slots).

Copper alternative (if you must)

• Use outdoor‑rated, gel‑filled, solid‑copper Cat6 (no CCA). Pull it in its own conduit as above.
• Install listed Ethernet surge protectors at both buildings and bond them to the local grounding electrode system.
• Maintain separation from power (12 in. in earth; cross at 90°). Do not share a conduit with power.
• Keep total length under 100 m. For PoE devices, stick to high‑quality cable and minimize patch length.

Safety considerations

• Always call 811 before digging.
• Wear PPE and watch for utility marks and roots/rocks.
• Use GFCI‑protected power for tools outdoors.
• Seal building penetrations to prevent water intrusion and rodents.

Tips for best results

• Oversize the conduit to 1 in. and pull a spare fiber or leave a spare pull string for future upgrades.
• Use long‑sweep 24 in. radius elbows for easy pulls, especially with pre‑terminated fiber.
• Add a small outdoor NEMA box at stubs to protect connections and act as a pull point.
• Label everything and document the route with photos and measurements from fixed landmarks.

Common mistakes to avoid

• Running copper Ethernet between buildings without surge protection and bonding—high risk of equipment damage.
• Sharing a conduit with power conductors—violates code and invites interference.
• Too many tight bends—makes pulling difficult and can damage cable.
• Buying copper‑clad aluminum cable—poor performance and heat issues with PoE.
• Skipping warning tape or route documentation—harder and riskier for future digging.

When to call a pro

• You can’t maintain required separations from existing power or need to share a trench with utility work.
• You prefer field‑terminated fiber, fusion splicing, or need certification testing for business/insurance.
• The run crosses a driveway or public right‑of‑way that may need boring permits.

Done right, a fiber‑in‑conduit run gives you fast, stable networking to your garage with minimal code hassle and strong protection from lightning and surges.