To make a twisted-pair network cable, measure the run, cut the cable 30 cm longer than the distance, strip the jacket, arrange the eight conductors in T-568B order at both ends, crimp an RJ45 plug on each end and test the finished cable. Keep each fixed run to 90 m so that patch cables at both ends stay inside the 100 m channel limit, and use the same wiring order at both ends for a straight-through cable. Salvaged building cable is the usual source, and every cable must be tested before it is trusted.
Part of Networking
Planning, cutting, laying and terminating copper network cable, as the practical build companion to the theory of twisted pairs.
Plan The Whole Run Before Cutting Any Cable
Twisted Pair Wiring explains why the cable works (differential signalling, twist rate, categories, solid versus stranded). This article is the build order. The decisions come first because a cable cut too short cannot be extended and a run that exceeds the length limit cannot be fixed with better connectors.
The length rule comes from Star Topology: a fixed run of no more than 90 m, leaving 10 m for patch cables at the two ends, for a 100 m channel. Solid cable goes in walls and stranded cable makes the short patch leads that get flexed (Twisted Pair Wiring). Salvaged telephone cable is usually Cat3, which Physical Connections rates for 10 Mbps Ethernet only; do not count on more from it.
What You Need
- Cable — solid-core twisted pair for fixed runs; the carrier Internet Infrastructure names 24 AWG solid copper in twisted pairs salvaged from building wiring
- RJ45 plugs and a crimping tool — see Cable Crimping
- A cutter and a jacket stripper — a sharp knife works if you do not nick the conductors
- A tester — Cable Testing
- Labels and a marker
Method: Make And Lay A Cable
Step 1: Measure the route, not the straight line Follow the real path through walls, around corners and up to the ceiling. Add 30 cm for excess, as the carrier does, and then check the total is still within 90 m for a fixed run. Pull a fixed run from the destination end (Twisted Pair Wiring) so spare cable ends up at the equipment, not stuck in the wall, and never bend tighter than the minimum bend radius, typically 8 times the cable diameter for Cat6.
Step 2: Keep it away from other wiring Separate it from mains wiring and cross at 90 degrees rather than run alongside; see Physical Infrastructure for the conflicting separation figures in this section and use the larger.
Step 3: Strip the jacket and keep the twist The carrier strips 3 cm of jacket. Untwist only as much as needed to seat the conductors, and no more than 13 mm for Cat5e (Twisted Pair Wiring).
Step 4: Arrange in T-568B order Pin 1 to 8: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown. A straight-through cable uses this order at both ends. A crossover cable uses T-568A at one end and T-568B at the other, and is rarely needed because modern switches detect the crossover automatically (Twisted Pair Wiring).
Step 5: Terminate and test Crimp the plugs as described in Cable Crimping, then test the cable before it is hidden behind a wall plate. Label both ends.
Worked Example: Cable For A Clinic Wing
Eight rooms, each with one socket, at an average of 25 m from the closet. Total cable: 8 x 25 = 200 m. The carrier’s 30 cm excess per cable adds 8 x 0.3 = 2.4 m, so about 202.4 m, and a real job needs a margin for the longest runs and for mistakes. If the longest route measures 88 m, adding 0.3 m gives 88.3 m, which is inside the 90 m limit. A route that measures 95 m is not: move the closet or add a second one rather than stretch the run.
Common Mistakes
- Pulling cable by the connector — the plug is crimped on afterwards for exactly this reason; pull bare cable and terminate after installation
- Using stranded cable for a fixed run, or solid cable for a flexed patch lead — Twisted Pair Wiring says never do either
- Wiring two ends in different orders by accident — a cable with T-568A at one end and T-568B at the other is a crossover; label deliberate crossovers
- Not testing — a bad run behind a wall is far harder to find than one on the bench
Safety
Cable near mains and between buildings
Do not pull network cable through a conduit or box that carries mains wiring, and do not strip or splice cable in a wall that you have not proved dead. Copper cable between separate buildings is a path for lightning surges; prefer fibre (Fiber Optics) and see the lightning guidance in Physical Layer. Cutting tools slip: cut away from your hand.
What’s Next
- Learn next: Cable Crimping — the termination step in detail
- Combine with: Connectors — how RJ45 plugs and the alternatives work