Twisted Pair Basics: Choosing Cat5e or Cat6, and Whether 100 m Can Be Exceeded

Why video still runs on twisted pair

Even with fibre and wireless widely available, IP cameras and most job sites still run on twisted pair. The reasons are practical: low cost, simple installation, native interface match on switches, extenders and cameras, and power riding along with data (PoE/PoC).

The usual choices are Cat5e and Cat6: Cat5e for Fast Ethernet, Cat6 for Gigabit. Video-over-CAT extenders also state the required category, so follow the equipment specification.

Choosing the category: Cat5e or Cat6

	Cat5e	Cat6
Typical use	Fast Ethernet, general camera drops	Gigabit, 4K extension, high-bandwidth work
Standard conductor gauge	About 0.50 mm	About 0.56 mm
Loop resistance, 300 m box	About 27–30 Ω	About 21–24 Ω
Cost	Lower	Higher

Conductor gauge: standard vs substandard

Gauges on the market vary widely and substandard cable is common. Standard reference values: Cat5e about 0.50 mm, Cat6 about 0.56 mm.

Substandard cable sells on its printed category while being thinner and adulterated. The damage does not appear on installation day — it appears months later: intermittent signal, dropouts when night mode switches, widespread failures after a damp season. That rework costs far more than the cable savings.

Material: how the five common types really compare

Five materials are common, listed from worst to best:

Material	What it really is	Verdict
Alloy	Cheapest; essentially iron-based	Worst option; not for any permanent installation
Copper-clad aluminium (CCA)	Mainly aluminium; oxidises, and resistance rises as it does	Classic symptom: fine at first, intermittent months later
"High-conductivity silver"	Despite the name, still aluminium — marginally better than CCA	Note: it contains no silver; do not be misled
Pure copper	Better than aluminium, but resistance still relatively high	Usable, but not for long runs
Oxygen-free copper	Currently the best material under the standard	Recommended for surveillance and video transport

A multimeter acceptance test

Beyond buying a reputable brand, learn to verify. The practical method is measuring the resistance of a full box:

1. A box is typically 300 m (about 305 m in practice).
2. Measure the loop resistance of the whole box with a multimeter.
3. Reference values: Cat5e about 27–30 Ω, Cat6 about 21–24 Ω.
4. Materially higher than reference → thin gauge or adulterated material; reject it.

No specialist instrument needed — do it on delivery, and it filters out most substitution. Worth writing into the acceptance checklist.

Where the 100 m limit comes from

Accounts of "120 m works fine" usually omit context:

• Signal attenuates and packets are lost. Beyond 100 m you may still get a picture, but the error rate rises — occasional frame loss, worse at night or at high bitrate.
• No headroom remains. Cable ageing, connector oxidation and temperature or humidity changes all consume margin. Working today does not mean working next year.
• Later failures are expensive. With no margin left to tune, the only remedy is re-cabling.

The right answer beyond 100 m is not gambling but adding a repeater (switch or active extender) or moving to fibre. Fibre beats stacked repeaters on both cost and stability over distance.

Four selection rules

1. Fix the category, then the material: category by bandwidth and device requirement (Cat5e for general cameras, Cat6 for gigabit or 4K); material ideally oxygen-free copper.
2. Always measure resistance on delivery: one measurement per box, logged, as acceptance evidence.
3. Design to 100 m, not 120 m: spend headroom on time and environment, not on luck.
4. Beyond the limit, use fibre or a repeater: "it works right now" is not a design criterion.