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Coaxial Cable for Access Control Systems: Reliable Connections for Secure Doors

Coaxial cable, often recognized by its distinctive round shape and threaded metal connector (F-type or BNC), might seem like a relic from older CCTV systems. Yet, ​coaxial cable remains a relevant, reliable, and often preferable choice for key components within modern access control installations. Understanding where and why it’s used helps ensure robust security performance.

Why Coax for Access Control?

Unlike complex IP-based networks transporting data packets, access control primarily relies on transmitting ​simple electrical signals and low-voltage power over moderate distances. Coaxial cable excels at this in specific scenarios due to:

1. ​Shielded Construction: The core signal conductor is encased within layers of insulation and a metallic foil + braid shield. This effectively ​minimizes interference from electrical noise (like motors, fluorescent lights, or nearby power cables) and radio frequencies (RFI) that could disrupt critical signals like door contact status or reader communication.
2. ​Signal Integrity over Distance: While distance limitations exist (more on that below), coax maintains signal strength and quality much better than unshielded twisted pair (UTP) cables like Cat5e/Cat6 for the specific signals used in access control peripherals. This prevents glitches.
3. ​Simplicity & Reliability: Connecting devices with coax is generally straightforward. Screw-on connectors provide a secure, vibration-resistant connection less prone to accidental disconnection than RJ45 plugs in some environments.
4. ​Proven Cost-Effectiveness: For its intended purpose within an access system, quality coaxial cable is often a lower-cost solution compared to running shielded twisted pair, especially where noise is a known issue.

Where is Coax Typically Used in Access Control?

You won’t typically find coax connecting the main access control panel/controllers to the network (that’s Ethernet/Cat cable). Instead, it excels in connecting ​peripheral devices to controller inputs and outputs:

1. ​Door Position Monitors (Door Contacts): The single most common coaxial cable application. The cable connects a ​normally closed (NC) or ​normally open (NO) magnetic reed switch (the contact) installed on the door and frame back to an ​input on the access control panel or door controller. When the door opens, the contact opens (or closes, depending on type), changing the electrical state on the coax cable, signaling the controller that the door is ajar. Coax’s shielding is vital here to prevent false “door forced” or “held open” alarms caused by electrical noise.
2. ​Request-to-Exit (REX) Devices: Motion detectors or push buttons (REX devices) signaling that someone inside wants to exit often use coaxial cable to connect back to a controller ​input. Their signal needs similar noise immunity.
3. ​Powering Auxiliary Devices (Often Paired Cable): Some specialized coaxial cables, particularly ​Siamese Coax (RG59-Si or RG6-Si), combine a coaxial cable with a separate 2-conductor pair (typically 18 AWG or 16 AWG). This is incredibly useful:
   • ​Powering Door Strikes or Magnetic Locks: The low-voltage DC power required by electric locks can be carried simultaneously with the door contact signal over a single Siamese cable run. This simplifies wiring significantly.
   • ​Powering Readers: While many modern readers use Power-over-Ethernet (PoE), older or specific models might use the auxiliary pair in Siamese cable for low-voltage power.

Key Coaxial Cable Types for Access Control:

1. ​RG59: The traditional standard. Good for distances up to ​300-500 feet (91-152 meters), suitable for most door contact and REX runs within a building. More flexible than RG6, making pull-through conduit easier. Use ​copper-clad steel (CCS) or solid copper core (better).
2. ​RG6: Features a thicker center conductor and better shielding than RG59. Performs better over ​longer distances (up to 600+ feet / 183+ meters) and offers superior noise rejection. Ideal for longer cable pulls, electrically noisy environments (industrial settings, near large motors), or if higher-quality signal transmission is critical.
3. ​RG59-Siamese / RG6-Siamese: Essential for the power+signal applications mentioned earlier. Combines RG59 or RG6 coax with a separate 2-conductor (usually 18 AWG or 16 AWG) power pair. ​Choose the gauge (AWG) of the power pair based on the lock/reader power requirements and total distance (voltage drop matters!).
4. ​Weatherproof / Burial Rated: For any cable running outside, in conduit exposed to moisture, or directly buried, select RG59 or RG6 explicitly rated for these conditions. Look for a dense UV-resistant jacket and flood protection. RG6 is generally preferred outdoors due to its superior shielding.

Important Considerations for Installation:

• ​Distance Limits: Always adhere to the maximum recommended distances specified by the cable manufacturer and, critically, by your ​access control panel/lock/reader manufacturer. Signal attenuation (loss) increases with distance. For powering locks via Siamese cable, voltage drop over distance is crucial – calculate required wire gauge and verify power availability at the lock location.
• ​Connectors: F-Type connectors are most common. Use ​crimp-on connectors designed specifically for your cable type (RG59 or RG6) for a reliable, weather-resistant connection. Seal outdoor connections properly. Avoid soldering unless highly skilled – poor solder joints cause faults.
• ​Avoiding Kinks and Pinches: Sharp bends or crushing the cable damages its internal structure and shielding, compromising signal integrity. Use conduit sweeps and careful pulling techniques.
• ​Noise Sources: While shielded, it’s still best practice to route coaxial cable away from known sources of interference (heavy motors, high-voltage power lines, large transformers, fluorescent light ballasts) wherever possible. Maintain separation from power cables.

Coax vs. Ethernet (Cat5e/Cat6):

• ​Use Coax For: Simple binary signals (door contacts, REX), especially in noisy environments, and combined signal+power via Siamese.
• ​Use Ethernet/Cat Cable For: Connecting access control panels/controllers to the network, communicating with IP door controllers, IP readers (which use PoE), and transferring complex data streams. Shielded twisted pair (STP/FTP) offers good noise immunity but is often more expensive than coax for peripheral devices.

Conclusion

Coaxial cable remains a fundamental, cost-effective, and highly reliable wiring solution for core functions in access control systems, especially for monitoring door status and connecting REX devices. Its robust shielding provides crucial noise immunity, while Siamese versions offer unparalleled convenience for powering electric locks alongside signal transmission. Choosing the right type (RG59, RG6, or Siamese), respecting distance limits, using quality connectors, and installing correctly ensures years of trouble-free operation for the critical security perimeter of your doors. For your next installation or troubleshooting project involving door contacts, remember: coaxial cable is a proven workhorse.