Which factor primarily limits data signal reliability in PoE when the cable is too long?

Which factor primarily limits data signal reliability in PoE when the cable is too long?

• A. Power rating
• B. Wavelength
• C. Cable length
• D. Temperature

Answer: (C)

The main factor is the length of the cable itself. On copper twisted-pair used for PoE, longer runs cause more signal loss (attenuation) and greater propagation delay, which together reduce the voltage and timing margins the receiver needs to reliably distinguish data bits. Once the cable is too long, the data signal can fall below the receiver’s threshold or become too distorted, leading to errors and reduced reliability. That’s why Ethernet/Poe links over copper are typically limited to about 100 meters; beyond that, you need repeaters/switches or convert to fiber. Wavelength isn’t a factor on copper, and while temperature and power loss can affect performance, they’re not the primary limiter for data reliability on long runs.

The main factor is the length of the cable itself. On copper twisted-pair used for PoE, longer runs cause more signal loss (attenuation) and greater propagation delay, which together reduce the voltage and timing margins the receiver needs to reliably distinguish data bits. Once the cable is too long, the data signal can fall below the receiver’s threshold or become too distorted, leading to errors and reduced reliability. That’s why Ethernet/Poe links over copper are typically limited to about 100 meters; beyond that, you need repeaters/switches or convert to fiber. Wavelength isn’t a factor on copper, and while temperature and power loss can affect performance, they’re not the primary limiter for data reliability on long runs.