1. Structural Differences: The Shield's "Secret Weapon"
The shield of a shielded cable is essentially a layer of conductive material, typically composed of aluminum foil, copper mesh, or a metal braid, wrapped around the cable's insulation (or around each twisted pair). This layer, when grounded, directs external electromagnetic interference to the earth while preventing internal signals from radiating outward, providing bidirectional protection.
Unshielded cables (such as common UTP network cables) rely entirely on the physical structure of the twisted pairs to offset interference. The balanced twisting of the wire pairs reduces electromagnetic coupling, but lacks active shielding, resulting in weaker interference resistance.
2. Visual Identification: Tips for Seeing Through a Cable at a Glance
1. Observe the Cross-Section:
Peel back the cable jacket. If you see a metal foil wrapping or a dense metal braid (similar to the structure of bulletproof vests), it's a shielded cable. If only the wire pairs are covered by insulation, it's an unshielded cable.
2. Cable Sheath Identification:
Shielded cables are typically labeled "STP" (shielded twisted pair), "FTP" (aluminum foil shield), or "SFTP" (aluminum foil and metal mesh double shield); unshielded cables are labeled "UTP."
3. Feel Differences:
Due to the additional metal layer, shielded cables are often stiffer and heavier than unshielded cables of the same specifications.
III. Performance Comparison: Which One Best Fits Your Needs?
1. Interference Resistance:
Shielded cables can withstand strong interference sources such as factory equipment, high-voltage power lines, and radio equipment, making them suitable for high-precision applications like industrial automation and medical equipment. Unshielded cables are more cost-effective in low-interference environments like homes and offices.
2. Transmission Distance and Speed:
Shielded cables, due to their low signal loss, are more suitable for long-distance transmission (over 100 meters) or high-frequency signal transmission (such as HDMI 2.1 and 10GbE). Unshielded cables offer stable performance over shorter distances.
3. Installation Cost:
Shielded cables require strict grounding, and connectors require specialized metal shielding heads. This makes installation complex and costly. Unshielded cables are simple to route and offer lower maintenance costs.
IV. Selection Mistakes: Avoid These Pitfalls!
1. "Shielded cables are always better than unshielded cables":
Using shielded cables in environments without strong interference may introduce noise due to poor grounding, which is costly.
2. "Twisted-pair cable can replace shielding":
Twisted-pair cable only suppresses low-frequency interference and is virtually ineffective against high-frequency interference (such as 5G signals). Shielded cables are essential in these situations.
3. "The shield can be grounded at any point":
Incorrectly grounding at a single point can cause the shield to act as an "antenna." The correct approach is to connect the shield to the system ground point to avoid loop currents.
V. Ultimate Selection Guide
1. Choose shielded cable:
Around motors, inverters, and broadcast base stations
Transmitting high-frequency signals such as HD video and gigabit Ethernet
Scenarios requiring EMC (electromagnetic compatibility) certification
2. Choose unshielded cable:
Home networks, general office environments
Short-distance (<50 meters) data transmission
Budget-limited and interference-controllable
