Category 3 cabling is the third-lowest grade of unshielded twisted-pair (UTP) cabling.
What is Category 3 cabling?
Category 3 Cabling is the third-lowest grade of unshielded twisted-pair (UTP) cabling. Category 3 cabling was designed to support digital voice and data communication at speeds up to 10 Mbps.
It uses 24-gauge copper wires in a configuration of four twisted-pairs enclosed in a protective insulating sheath. Category 3 cabling is the lowest grade of UTP cabling that can support standard 10BaseT types of Ethernet networks and was often used for legacy 4-Mbps Token Ring installations
Category 3 cabling still has an installed base in older buildings where it is often cheaper to use the existing cabling than to upgrade to newer grades.
Installing higher-grade cabling for backbone cabling in vertical rises and elevator shafts can extend the life of work areas that still use category 3 cabling. However, if greater speeds are required at users’ workstations, the best solution is to rewire the work areas using category 6 cabling.
Category 3 Cabling Characteristics
The following table summarizes the electrical characteristics of category 3 cabling at different frequencies, which correspond to different data transmission speeds. Note that attenuation increases with frequency, while near-end crosstalk (NEXT) decreases.
| Characteristic | Value at 10 MHz | Value at 16 MHz |
| Attenuation | 27 decibels/1000 feet | 36 decibels/1000 feet |
| NEXT | 26 decibels/1000 feet | 23 decibels/1000 feet |
| Resistance | 28.6 ohms/1000 feet | 28.6 ohms/1000 feet |
| Impedance | 100 ohms (± 15%) | 100 ohms (± 15%) |
| Capacitance | 18 pF/feet | 18 pF/feet |
Source: ANSI-TIA-EIA 568-B – Commercial Building Telecommunications Cabling Standard
