⏱ Latency
~0.1–0.3 ms switch-to-PC on copper vs 3–20 ms on busy Wi-Fi. For gaming, calls and music production that gap is everything.
Ethernet consistency — 96/100
01 · WHY ETHERNET STILL WINS
Wi-Fi is magic. Copper is a promise.
Radio is shared, half-duplex airtime that your neighbours, microwave and fish-tank all fight over. A twisted pair is yours — full-duplex, deterministic, sub-millisecond, and it carries power too.
📦 Throughput that sticks
A “1 Gbps” Wi-Fi link delivers ~300–500 Mbps real-world, shared. A Cat 6 run delivers 1,000 Mbps, all day, every device, simultaneously.
Sustained speed — 92/100
🔌 Power + data
PoE++ pushes 90 W down the same pairs — cameras, APs, lighting, door entry. Try that over thin air.
One-cable devices — 88/100
Run copper when…
- Desks, TVs, consoles, printers, servers
- Anything that must not buffer, drop or lag
- Backhauling mesh Wi-Fi nodes (!!)
- PoE cameras, APs, smart lighting
- You own the walls — always pull 2 drops
Use Wi-Fi when…
- Phones, tablets, guests, the garden
- Renting / can't drill
- IoT sensors sipping milliwatts
- …fed by copper backhaul, obviously
02 · A BRIEF HISTORY OF GETTING FASTER
From 2.94 Mbps memo
to 40 gigs over copper.
1973
Metcalfe sketches Ethernet
Xerox PARC memo. Coax, 2.94 Mbps, “Ether” as in luminiferous.
1983
IEEE 802.3 · 10BASE5
Thick coax “vampire taps”. 10 Mbps, 500 m segments.
1990
10BASE-T arrives
Twisted-pair + star topology. The RJ45 era begins.
1995
Cat 5 · 100BASE-TX
100 MHz cable, 100 Mbps. The office gets wired.
1999
Gigabit · 1000BASE-T
All 4 pairs, both directions, echo cancellation. Black magic.
2006
10GBASE-T
10 Gbps over copper. PAM-16, LDPC, 500 MHz Cat 6A.
2016
Cat 8 · 25/40GBASE-T
2 GHz, 30 m. Copper storms the datacenter top-of-rack.
Today
Single-pair + 10G to desk
802.3da automotive 10 Mbps single-pair; Cat 6A to every desk as standard.
03 · KNOW YOUR CATS
Every category, no marketing fog.
Live data from the Bun backend (GET /api/cables). Filter by what you actually need — 10-gig reach is the column that matters.
| Cable | Freq | Max speed | 10G reach | Shield | Cost | Pull it for… |
|---|
House rule: new walls get Cat 6 minimum, Cat 6A if you can. The cable is 10% of the job — labour is the rest. Pull two drops per location and a pull-string for later.
04 · ANATOMY OF A CABLE
Seven layers between you
and raw physics.
Hover / tap a layer →
Outer jacket
PVC for patch leads, LSZH for indoors, CMP plenum where air circulates, UV + gel-filled outside. The jacket is a fire, sunlight and crush rating — not decoration.
- Jacketfire + sun + crush rating
- Braid shieldS in S/FTP — alien crosstalk armour
- Foil per pairF in F/UTP — wraps each pair
- Spline separatorplastic cross keeping pairs apart
- 4 twisted pairsdifferent twist rates per pair
- Copper conductors23–24 AWG, solid or stranded
05 · WHY TWIST? (LIVE PHYSICS)
Noise hits both wires.
The twist makes it cancel itself.
cancels 92% of noise
Each pair carries +V and −V (differential signalling). Interference adds the same spike to both wires — the receiver subtracts them and the spike vanishes. Twisting ensures both wires sample the same field on average; tighter twist = higher-frequency rejection.
- Different rates per pair stop pairs talking to each other (crosstalk).
- Untwist > 13 mm at the plug destroys the effect — that's the #1 DIY failure.
- 10GBASE-T adds DSP echo-cancellation on top, per pair, 800M baud.
06 · SHIELDING DECODER
U/UTP? S/FTP? Read it like a label.
Format is X/YTP — shield around all cables / shield around each pair. Click a code to see where it belongs.
U/UTP — the default
Four naked twisted pairs in a jacket. Perfect for homes and clean offices. Cheapest, thinnest, easiest to terminate. Loses to motors, VFDs, fluorescent ballasts and 200-cable bundles — that's when you pay for foil.
⚠ Grounding rule: shielded cable must be bonded at ONE end (the patch panel). Ground both ends and you build a ground-loop antenna that performs worse than UTP.
07 · PICK THE RIGHT COPPER
Solid vs stranded.
Plenum vs riser. Get it right once.
🧱 Solid-core → in the walls
Single thick conductor per wire. Holds a punch-down IDC blade gas-tight for decades, lower attenuation. Never flex it daily — it work-hardens and snaps.
90 m horizontalpunch-down keystones23 AWG
🎧 Stranded → patch leads
Dozens of hair-thin strands. Survives bending, coiling, chair wheels. Slightly lossier — that's why patch + equipment cords are capped at 10 m total.
flex-ratedcrimp plugs26–24 AWG
🔥 CMP plenum → air spaces
Drop-ceilings and ducts that carry air. Plenum jackets char and self-extinguish with low smoke. Code-mandated in air-handling spaces in most jurisdictions.
CMPLSZH indoors
🏢 CMR riser → floor to floor
Vertical shafts between floors. Flame-retardant so fire doesn't ride the shaft. Cheaper than plenum. Outdoors? UV + gel-filled or conduit — indoor jackets die in a summer.
CMRCMX outdoor
08 · 3D · THE RJ45 UNDER A MICROSCOPE
Drag it. Spin it. Click a pin.
Procedural Three.js model — 8 gold contacts, 8 colour-coded conductors, clip and all. Hover pins to see which wire each one bites.
Pin 1 → White/Orange (T568B) — Transmit+ for 10/100, bidirectional for gigabit+.
09 · WIRING — A vs B, STRAIGHT vs CROSSOVER
Eight wires. Zero forgiveness.
END 1 · T568B
⇄ pairs 2 & 3 swap in crossover
END 2 · T568B
When straight? When crossed?
Straight (same both ends): everything through a switch — 99% of life. Crossover (pairs 2↔3 swapped): like-to-like before Auto-MDIX — PC↔PC, switch↔switch, ancient uplink ports. Modern ports auto-sense, so crossover is now mostly trivia + exams.
Split-pair trap 🪤
A continuity tester can pass a split pair (e.g. pin 3 wired with the wrong white). It'll “work” at 10 Mbps and collapse at gigabit. Only a qualification/certification test catches it. Keep pairs together!
10 · TERMINATION LAB — DO IT LIKE A PRO
Terminate a jack in 9 steps.
What you need: cable stripper, 110 punch-down tool, keystone jack, side cutters, tester. Optional but loved: cable comb, sharpie, velcro (never zip-ties on bundles).
1
Strip 40 mm, don't nick
Score the jacket only, flex and slide off. Nicked copper = future break. Keep twists intact.
2
Fold back rip-cord & spline
Cut the plastic cross flush. Fan pairs out in order — no crossing over each other.
3
Order per T568B
WO-O · WG-G · WB-B · WBr-Br across the jack's colour map. Double-check before seating.
4
Keep twist to the blade
Dress each wire into its IDC slot with twist preserved to < 13 mm from contact.
5
Punch, don't push
110 tool blade-out, one firm strike per wire. It seats and trims the tail.
6
Inspect the blades
Copper should be fully sunk, tails cut, no copper showing beyond the cap.
7
Cap it & seat it
Snap the dust cap / wire holder, click jack into plate or panel.
8
Same standard both ends!
A on one end + B on the other = accidental crossover. Label the run.
9
Test, then trust
Wiremap first, length + PoE load next. Re-terminate any pair that isn't perfect.
🧰 Bench checklist
11 · TESTING & TROUBLESHOOTING
Break it here, not in the wall.
A wiremap simulator. Inject a fault, then read the tester like it's 11 pm and the client demo is tomorrow.
Fault injector
1 2 3 4 5 6 7 8 → all pass
Clean sweep. Ship it.
What each tool tells you
- $15 continuity tester — opens, shorts, miswires, split pairs (basic). Finds 80% of DIY faults.
- $300 qualifier — length per pair, PoE load, speed capability. The sweet spot for installers.
- $1,500+ certifier — NEXT, return loss, alien crosstalk vs the CAT spec. The warranty paper.
Top 5 field faults
- Untwist > 13 mm at jack
- A on one end, B on the other
- Nicked conductor from stripping
- Stranded wire in a solid-only IDC
- Kink tighter than 4× diameter
12 · POWER OVER ETHERNET
Data and dinner on 4 pairs.
PoE estimator (live · /api/poe)
…
What sips what
- VoIP phone / sensor — 5–10 W · af is plenty
- Camera + heater / Wi-Fi 6 AP — 20–30 W · PoE+
- PTZ camera / LED panel / laptop dock — 50–90 W · PoE++ 4-pair
Heat is the enemy: keep PoE bundles ≤ 24 cables, prefer 23 AWG Cat 6A, and never bury bundles in insulation.
13 · CABLE PICKER — ASK THE BACKEND
Tell us the job. Bun answers.
14 · SIGNAL LAB — ATTENUATION
Longer + hotter + faster = quieter signal.
15 · PROVE IT — 8 QUESTIONS
Earn your crimper badge.
Questions load from GET /api/quiz, scored by POST /api/quiz/score on the Bun backend.
16 · FIBRE — LIGHT IN GLASS
Copper runs out at 100 m.
Light keeps going for kilometres.
Fibre-optic cable guides laser light down a glass core by total internal reflection — no electrons, no crosstalk, no lightning surge, nothing to tap without cutting glass. Watch a ray ride the core:
modal dispersion: the limit
Multimode (50 µm core) lets light take many paths. Rays arrive at different times — modal dispersion — which smears fast signals. That's why OM1 dies at 33 m of 10G.
Single-mode (9 µm core) allows exactly one path. Almost no dispersion, ~0.4 dB/km loss: 10 km on cheap optics, 100 km+ with the right lasers.
- 850 nm VCSELs (cheap, short) feed multimode; 1310/1550 nm lasers feed single-mode.
- Fibre carries zero power — remote devices still need copper (PoE) or mains.
🌊 Multimode (OM1–OM5)
Fat 50–62.5 µm core, cheap 850 nm VCSEL transceivers, easy to connectorise. Reach: tens to hundreds of metres. The LAN/datacenter default inside buildings.
orange · aqua · lime jacketsLC duplex
🎯 Single-mode (OS2)
Hair-thin 9 µm core, laser optics, pennies-per-metre cable. Reach: kilometres. Use it between buildings, across campus, and anywhere you might want 100G later without re-pulling.
yellow jacketfuture-proof
Run fibre when…
- Over ~90 m — copper's limit is timing, not effort
- Between buildings (no copper = no lightning path)
- EMI hell: factories, hospitals, substations
- You want 40/100G+ later with only an optic swap
- Security matters — glass can't be clipped onto
Stick with copper when…
- Under 90 m to a desk, AP, camera, TV
- The device needs PoE power too
- Budget is tight and 10G is plenty
- You'll be re-terminating by hand a lot
17 · FIBRE TYPES — OM vs OS
Read the jacket like a label.
Live from the Bun backend (GET /api/fiber). Jacket colour is standardised — orange, aqua, lime, yellow — so you can identify glass from across the room.
| Fibre | Core | Light | 1G | 10G | 40/100G | Pull it for… |
|---|
House rule: between buildings or “might need 100G one day”? Pull OS2 — the cable is cheap, the labour isn't, and LR optics cost less than you think. Inside one datacenter row? OM3/OM4 with cheap SR optics.
18 · CONNECTORS + POLISH
LC won. MPO runs the big rooms.
LC — Lucent Connector
Tiny 1.25 mm ceramic ferrule, duplex clip holds TX+RX as one. ~70% of new LAN/SAN installs. Uniboot reversed-polarity patch leads fix TX/RX swaps without re-terminating.
⚠ Polarity matters: fibre is TX→RX, so one end must flip (Method A/B/C for MPO, A-to-B duplex patch). No link light? Swap the pair at one end first — it fixes half of all “dead fibre” calls. And APC (green, angled) must never mate with UPC (blue, flat).
19 · TERMINATING GLASS — SPLICING LAB
Don't connectorise by hand.
Splice a pigtail. Or buy pre-terminated.
Field-fitting individual connectors is a skill with a scrap bin. The sane paths: fusion-splice factory pigtails onto your pulled cable, use mechanical splices for one-offs, or skip all of it with a pre-terminated trunk + patch panels.
1
Strip to bare glass — gently
Remove jacket, aramid and 900 µm buffer with proper strippers. Glass cladding is 125 µm and scratches if you look at it wrong.
2
Clean, then cleave
Lint-free wipe + >99% isopropyl, then a precision cleaver for a mirror-flat 90° end-face. A bad cleave = a bad splice, always.
3
Fuse it
Fusion splicer aligns cores and arcs them together (~0.05 dB loss). Slide the heat-shrink sleeve over first — everyone forgets once.
4
Protect + park
Shrink the sleeve, coil service slack in the splice tray (≥ 30 mm bend radius), label both ends.
5
Test with light, not hope
Light-source + power meter (or OTDR for long runs) and keep the loss report. VFL red pen for continuity only — never for loss.
🕶 Safety: never look into live fibre (invisible IR burns retinas) · bin every offcut immediately — glass splinters are invisible and hate skin · isopropyl + wipes, no compressed-air cans on end-faces.
20 · LOSS BUDGET LAB
Every connector spends light.
Spend it on purpose.
21 · GLOSSARY + FIELD NOTES
Talk like a cable plant engineer.
AWG — American Wire Gauge
Lower = thicker. 23 AWG beats 24 AWG for PoE heat and attenuation. Cheap CCA (copper-clad aluminium) is banned from the standards — buy pure copper.
NEXT / AXT — crosstalk
Near-End Crosstalk: a pair shouting into its neighbour. Alien (AXT): neighbouring cables shouting in. Cat 6A's thickness is mostly alien-crosstalk armour.
Channel vs permanent link
Permanent link = the in-wall 90 m. Channel = link + 10 m of patch cords. Certify the right one for the warranty.
Auto-MDIX
Ports that detect straight vs crossover and adapt. Universal since gigabit — crossover cables are now exam trivia.
Keystone vs feed-through plugs
Keystones (punch-down) for solid in-wall cable. For plugs on solid: staggered or feed-through RJ45s — standard plugs are tuned for stranded.
Why two drops per location?
Labour dwarfs cable cost. The second drop carries a phone, AP, HDMI extender or redundancy — for ~$5 of copper while the walls are open.
OS vs OM — single vs multi
OS = Optical Single-mode (9 µm core, yellow, kilometres). OM = Optical Multimode (50 µm core, aqua/lime, hundreds of metres). Bigger OM number = more modal bandwidth, not a different size.
UPC vs APC polish
UPC (blue, flat) for datacom; APC (green, 8° angle) kills back-reflection for PON, RF video and long-haul. Never mate green to blue.
dB — deceive with Bell
Logarithmic: 3 dB = half the light gone. A 0.5 dB dirty connector eats ~11% of your signal; two of them plus margin can sink an SR link.
🎲 Random field fact (/api/facts/random)
…
⚡ Lightning rules
- Outdoor runs get shielded + grounded + surge protectors at building entry.
- Keep copper ≥ 300 mm from mains in parallel; cross mains at 90°.
- Velcro, never zip-ties. 25 mm bend radius minimum.