Cat3 Ethernet Cable: Specs, Features, Pros & Cons
Category 3 was the cable grade 10BASE-T ran on in the early days of twisted-pair Ethernet, and almost nobody installs it for data now. Its four unshielded pairs, tested to a modest bandwidth, end in an ordinary RJ45 connector that looks identical to the one on a modern cable.
Because of that resemblance, a Cat 3 patch lead plugs into any current switch or router and appears to work, while limiting the link to a fraction of what the equipment can do. In an older building, cable of this grade may still be sitting in the walls behind sockets that look perfectly modern.
Its tested bandwidth supports ten megabits per second across a full hundred-meter run and nothing beyond that, so there is no gigabit, no multi-gig, and none of the higher speeds later grades were designed around. Power over Ethernet is limited to the earliest and weakest specification.
The standards bodies have kept the category alive for voice work, such as the phone lines in an older office and the wiring frames they run back to, where its characteristics remain perfectly adequate.
For any new data installation it is the wrong choice, and its relevance now is diagnostic. If a network link is inexplicably slow in an older property, the grade printed on the cable jacket is often the answer, and it can be read wherever the cable is exposed, behind a wall plate, at a patch panel or above a ceiling tile.
Category strengths
Where the Cat3 Ethernet Cable trails the median
- A much lower maximum data rate ?0.01 Gbps vs 10 Gbps (median)
- A much lower bandwidth ?16 MHz vs 375 MHz (median)
- A much lower 10 Gigabit reach ?0 m vs 42.5 m (median)
- No 10 Gigabit Ethernet ?
- No recognition for new installs ?
- No Gigabit Ethernet ?
- No multi-gig (2.5G / 5G) ?
- No PoE++ (Type 4, 90 W) ?
How this VS Score was computed
Score 21: each known spec is measured against the median of all ethernet cables (8 products), then weighted; 50 means level with that median. In classes of six or more, a value beyond the class’s 10th–90th percentile range counts as that limit, so one extreme product cannot set the scale. 88% of the scoreable weight could be used; unknown values, features not applicable to this class and proxies (battery capacity where a rated life exists) add or remove nothing.
| Specification | This product | Cohort median | Score weight | Points moved |
|---|---|---|---|---|
| Maximum data rate | 0.01 — capped at the class’s lower range (1) | 10 | 3 | −135.0 |
| Native RJ45 connector | Yes | 75% of the class have it | 2 | +100.0 |
| 10 Gigabit reach | 0 | 42.5 | 2 | −96.0 |
| 10 Gigabit Ethernet | No | 63% of the class have it | 2 | −96.0 |
| Recognition for new installs | No | 75% of the class have it | 2 | −96.0 |
| Bandwidth | 16 — capped at the class’s lower range (100) | 375 | 2.5 | −92.5 |
| Gigabit Ethernet | No | 88% of the class have it | 1.5 | −72.0 |
| Multi-gig (2.5G / 5G) | No | 75% of the class have it | 1.5 | −72.0 |
| Shielded construction | No | 38% of the class have it | 1 | −48.0 |
| Alien crosstalk limits | No | 33% of the class have it | 1 | −48.0 |
| PoE++ (Type 4, 90 W) | No | 88% of the class have it | 1 | −48.0 |
| Reach at top speed | 100 | 100 | 1.5 | +0.0 |
| Typical shielding | U/UTP (unshielded) | U/UTP (unshielded) | 1.5 | +0.0 |
| Maximum PoE power | 15.4 — capped at the class’s lower range (90) | 90 | 1.5 | +0.0 |
Not scored: 25G / 40G Ethernet (not applicable: only 13% of this class have it); Conductor material (unknown: not scored); Snagless boots (unknown: not scored); Backward compatibility (standard for the class (100% have it)).
Editor’s note
Category 3 is the oldest twisted-pair grade still worth naming, and almost nobody buys it for data any more. It was the cabling that carried 10BASE-T when Ethernet first moved onto twisted pair, rated to 16 MHz and four unshielded pairs terminated in an ordinary RJ45. TIA has kept it in the standards, but for voice: telephone risers, analog extensions, and the punch-down blocks behind them. For anything carrying packets it was retired decades ago.
Sixteen megahertz of tested bandwidth supports 10 Mbit/s comfortably and nothing beyond it in practice. Cat 3 is specified only up to 16 MHz. There was a 100 Mbit/s standard designed to run on it, 100BASE-T4, which spread the signal across all four pairs to make up for the cable's limits, but it lost to 100BASE-TX on Cat 5 and disappeared from the market. Gigabit was never on the table.
One modern detail keeps Cat 3 relevant in old buildings: Power over Ethernet. The original 802.3af specification explicitly permits Cat 3 for lower power levels, so a legacy riser can still feed a 15.4-watt device such as a basic phone or a small access point. The higher PoE classes, from 30 watts upward, require Cat 5 or better, which rules Cat 3 out of anything modern with a camera or a light on it.
If you have found Cat 3 behind a wall plate, the practical question is not whether to use it but what it is feeding. Voice, alarm panels and door entry can stay. Anything that needs to move data should be repulled, and since the wall only needs opening once, repull to Cat 6a.
Specifications
Quality bars show where each figure sits between the lowest and highest of the 8 ethernet cables this VS Score is measured against.
Speed & reach
Construction & shielding
Power & connectors
Standards & status
Sources and verification
Where the specifications come from
- Official product pagewebstore.iec.ch
- Datasheet or manualstandards.ieee.org
Verification
- First published
- Specifications last checked
- Sheet completeness
- 20 of 28 specifications verified; the rest show as Unknown and are never estimated or scored
- Page type
- Product specification page — Compiled from the manufacturer’s published specifications and the cited sources; this is not a hands-on test.
- Basis
- Research-based: specifications and editorial text were compiled from the documents listed here and the manufacturer’s published data. We have not tested this unit ourselves; where independent measurements are mentioned they belong to the linked publication.
Ratings & reviews
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The bottom line
The Cat3 Ethernet Cable earns a VS Score of 21, below the median of the 8 ethernet cables it is measured against (a score of 50 is level with that median).
- Who it’s for
- Voice risers, alarm and door-entry wiring, and low-power PoE phones already sitting on legacy cable.
- Who should look elsewhere
- Any new data run, because it tops out at 10 Mbit/s and cannot carry gigabit at all.
- The trade-off that matters
- It is already in the wall, which is its only advantage, and every performance figure is a generation behind what modern equipment expects.
- The main alternative
- Cat6a Ethernet Cable: the grade to repull with once the wall is open
The VS Score is calculated from the weighted specifications above, each measured against the median of comparable ethernet cables — a shortlisting guide, not a substitute for your own priorities. See how we score.