Fibre Optic Cable vs Copper Wire: Bandwidth, Cost and Distance Compared

A network designer comparing a bill of materials rarely asks which cable is better. The real question is narrower: for this link, at this distance, with these devices on the far end, which medium costs less to own over ten years. The answer flips depending on where the run sits.

Take two live examples. A 10 Gbps link between racks 60 m apart: Cat6A copper does the job with passive cable and no optics at all. The same 10 Gbps requirement between two buildings 3 km apart: copper cannot reach it at any sensible price without adding active repeaters, while one single-mode fibre pair carries it with nothing in between. Neither outcome is surprising once the physics is on the table.

Bandwidth and reach: where the gap stops being theoretical

Single-mode fibre carries 10 Gbps roughly 40 km without regeneration. Cat6A copper carries the same 10 Gbps roughly 100 m. Between those two figures, most real decisions are already made.

The limits come from different physics. Copper attenuation and crosstalk climb steeply with frequency, so every doubling of throughput shortens the usable run; 10GBASE-T over Cat6A at 100 m already sits close to the edge of the standard. Single-mode glass at 1310 nm and 1550 nm loses about 0.35 dB per kilometre, which is why a fibre plant installed for 10G today will take 100G or 400G per wavelength later with only the transceivers swapped.

Capacity per cable matters as much as capacity per pair when tray and conduit space is tight. A single 12-fibre outdoor cable weighs roughly what one Cat6A run weighs and replaces a dozen copper runs. Past a few hundred metres, the copper option stops being a cheaper cable and becomes a chain of powered equipment.

For a procurement-focused version of the same trade-offs, this fibre versus copper decision guide walks through cost, distance and upgrade timing from the buyer side.

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Cost per connected link, not cost per metre

Copper is cheaper for short links. Fibre is cheaper per gigabit once a run passes roughly 100 m. Quoting either one per metre hides the number that actually matters.

Per metre, Cat6A and loose-tube single-mode cable are closer in price than most buyers expect. The difference sits at the ends. Copper terminates with a jack and a patch cord. Fibre needs fusion splicing, splice closures, pigtails and a transceiver at each end, and a single-mode module can cost more than the 100 m of cable it plugs into.

Labour shifts the balance again. Pulling 24 Cat6A cables through a riser takes longer and fills more tray than one 24-fibre cable, and every copper run needs its own termination and certification test. On dense builds the installation saving frequently offsets the optics bill. On a two-cable link it almost never does.

Power, interference and site conditions

Fibre is dielectric: it carries no current, radiates nothing and picks up nothing. Copper can deliver up to 90 W to a device over the same pair it uses for data.

Both facts are useful. In a substation, tunnel or rooftop where earth potential rise and lightning are real concerns, an all-dielectric cable removes the grounding question entirely, which is why aerial self-supporting designs are common along power routes. On a warehouse ceiling the opposite argument wins: a 90 W access point or camera needs no local mains supply, and copper is the simpler way to reach it.

Longevity separates them too. Copper oxidises at connectors in humid or coastal sites, and a corroded pair raises resistance, heats under load and eventually fails a certification test. Glass does not corrode, though fibre end faces still demand cleaning before every mating.

The last 100 metres: where the two media meet

Most buildings end up hybrid: fibre on the backbone and riser, then copper or fibre on the final drop to the desk, camera or access point. Designing per segment is normal practice, not a compromise.

• Devices that need PoE and sit under 100 m: copper.
• Runs beyond 100 m or between buildings: fibre.
• Dense desk areas where tray space is exhausted: fibre to the zone, copper inside it.
• Ports expected to move to 25G or 40G within their service life: fibre.

The drop segment is also where the cost argument changes shape. Factory-terminated fibre drop cable removes field splicing, and a single-fibre drop is often quicker to install than pulling a new Cat6A run through a finished wall.

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A five-step selection sequence

Run the decision in this order: distance, power, growth, environment, then budget. The first two steps eliminate most wrong answers before price is discussed.

1. Measure the real route, including slack and vertical rises. Anything past 90 m on copper is already a fibre question.
2. List what sits at the far end and how much power it draws. PoE devices under 100 m usually stay on copper.
3. Check the upgrade path. If the link must support 25G or higher during its life, specify single-mode now; re-cabling later costs far more than the optics.
4. Survey the environment: interference sources, flooding, rodent risk, earth potential, temperature swing. These choose the cable construction, not just the medium.
5. Only then compare total installed cost, including terminations, test gear, patch panels and power at the far end.

Installation and testing: two different disciplines

Fibre tolerates distance but not contamination. Copper tolerates contamination but not distance. Crews trained on one medium often damage the other on the first day.

• Bend radius: fibre cable is commonly rated at 20x outer diameter during installation and 10x once fixed. Exceeding it creates micro-bending loss that passes at 10G and fails at 100G.
• Splice loss: 0.1 dB typical and 0.3 dB frequently specified as the field maximum. A careless cleave costs more of the loss budget than a longer cable run.
• Testing: fibre needs an OLTS for loss and length plus an OTDR to locate events; copper needs a certifier for the permanent link and alien crosstalk at 10G.
• Contamination: one dust particle on an end face can add around 1 dB or scorch the connector under high optical power.

Questions buyers ask before they commit