Final answer:
The maximum length of copper Ethernet cable for a horizontal run according to TELUS standards is 100 meters.
Step-by-step explanation:
According to TELUS standards and the commonly accepted practices for Ethernet cabling, the maximum length of copper Ethernet cable that can be used in a horizontal run is 100 meters. This distance allows for appropriate signal strength and quality over copper cabling such as Cat5e and Cat6, beyond which signal quality could degrade.
It's worth noting that for special cases or with certain types of equipment, networks may see shorter maximum lengths. However, the standard for typical horizontal runs without additional signal boosting or specialized equipment is 100 meters. Coaxial cables and other media types might be subject to different constraints.