0.1 Copper Cables

Copper twisted-pair cable serves as the dominant medium for short-to-medium distance Ethernet links. Review the categories, construction, and standards before connecting any switch port.

Twisted-Pair Construction

Each cable contains 4 pairs of copper conductors. The pairs twist together at different rates (twist rates) to cancel electromagnetic interference (EMI) through differential signaling. The receiver measures the voltage difference between the 2 wires in a pair. Noise induced equally on both wires cancels out.

UTP (Unshielded Twisted Pair) relies entirely on twist rate for noise rejection. UTP cables cost less, weigh less, and terminate more easily.

STP (Shielded Twisted Pair) adds metallic shielding around individual pairs, all pairs, or both. Shielding variants:

Notation	Overall Shield	Per-Pair Shield
U/UTP	None	None
F/UTP	Foil	None
S/FTP	Braid	Foil per pair
SF/FTP	Braid + Foil	Foil per pair

Note

STP requires proper grounding at 1 end only. Grounding at both ends creates a ground loop that introduces noise.

In industrial environments, select STP (S/FTP or F/UTP) due to motor drives, VFDs, and other EMI sources.

Cable Categories

Category	Max Speed	Max Bandwidth	Max Distance	Notes
Cat 5e	1 Gbps	100 MHz	100 m	Minimum for modern installs
Cat 6	1 Gbps / 10 Gbps*	250 MHz	100 m / 55 m	*10G limited to 55 m
Cat 6A	10 Gbps	500 MHz	100 m	Augmented; required for 10GBase-T
Cat 7	10 Gbps	600 MHz	100 m	S/FTP only; uses GG45 or TERA connector
Cat 7A	10 Gbps	1000 MHz	100 m	Designed for future bandwidth needs
Cat 8	25/40 Gbps	2000 MHz	30 m	Data center top-of-rack only

Note

Cat 7 and Cat 7A are ISO/IEC standards, not TIA/EIA standards. Most enterprise and industrial deployments use Cat 6A as the highest practical choice.

TIA-568 Wiring Standards

The TIA/EIA-568 standard defines 2 pinout schemes for RJ45 connectors: T568A and T568B.

T568A pinout (RJ45, looking at the clip-down side):
Pin 1: White/Green
Pin 2: Green
Pin 3: White/Orange
Pin 4: Blue
Pin 5: White/Blue
Pin 6: Orange
Pin 7: White/Brown
Pin 8: Brown

T568B pinout:
Pin 1: White/Orange
Pin 2: Orange
Pin 3: White/Green
Pin 4: Blue
Pin 5: White/Blue
Pin 6: Green
Pin 7: White/Brown
Pin 8: Brown

Straight-through cable: both ends use the same standard (T568B–T568B is most common). Use straight-through cables to connect unlike devices (PC to switch, switch to router).

Crossover cable: 1 end uses T568A, the other end uses T568B. Crossover cables historically connected like devices (switch to switch). Modern switches with Auto-MDI/MDIX detect and correct the wiring automatically. Crossover cables are largely obsolete.

Note

The only difference between T568A and T568B: the green and orange pairs swap positions. Pairs 1 (blue) and 4 (brown) remain identical in both.

1000Base-T and 10GBase-T Pair Usage

• 10/100Base-TX: uses only 2 pairs (pins 1,2 and 3,6)
• 1000Base-T: uses all 4 pairs simultaneously, bidirectional on each pair
• 10GBase-T: uses all 4 pairs with advanced DSP. Requires Cat 6A or better.

Power over Ethernet (PoE)

PoE delivers DC power over the same cable as data. Relevant IEEE standards:

Standard	Max Power (PSE)	Pairs Used	Common Use
802.3af (PoE)	15.4 W	2 pairs	IP phones, basic cameras
802.3at (PoE+)	30 W	2 pairs	PTZ cameras, APs
802.3bt (PoE++)	60 W / 100 W	4 pairs	Industrial devices, displays

Note

In OT environments, verify that PoE-powered devices are rated for the voltage range. Some industrial sensors lack PoE design and sustain damage from PoE power.

Maximum Cable Run and Patch Cord Budget

The 100 m limit for structured cabling breaks down as follows:

• 90 m permanent link (wall to patch panel)
• 10 m combined patch cords (both ends)

Exceeding the 100 m limit causes signal degradation, increased bit-error rates, and link instability at 1G and 10G speeds.

Industrial Copper Cabling Considerations

• Use S/FTP Cat 6A in environments with heavy EMI (motor rooms, substations)
• Select industrial-grade RJ45 connectors with IP67 rating where moisture is present
• Route data cables perpendicular to power cables. Cross at 90° when paths intersect.
• Use cable trays with separation between power and data runs (minimum 200 mm without shielding)
• In hazardous areas (ATEX/IECEx zones), use intrinsically safe or explosion-proof rated cabling systems