CAN Wiring - A Practical Reference Guide
Principle 2: Keep Drop Cables (Droppers) Short While the backbone can be quite long (up to 40 meters for STAR range), the length of the cables that drop from the backbone to each device is strictly limited. Why is drop length critical? Each drop cable acts as an unterminated branch, or "stub," off the main backbone. On these stubs, signal reflections can still occur. While minor reflections from very short stubs are tolerable, longer stubs create significant reflections that can corrupt data on the main backbone. The longer the stub, the more destructive the reflection. The Drop Length Rule The maximum allowable length for a drop cable depends on the network's data rate (baud rate). For the most common standards: • NMEA 2000: Maximum cumulative drop length is 78 meters, but no single drop cable should exceed 6 meters (20 feet). Best practice is to keep them as short as possible.
As a universal rule of thumb: Always use the shortest drop cable possible for your installation.
Good vs. Bad Drop Length: Backbone <--------------------------------------> | | | <- Good
[Long Drop -> BAD]
| (< 6m)
|
[Device]
[Device]
Summary of Best Practices • Use Two 120Ω Resistors: One at each physical end of the backbone. No exceptions. • Build a Linear Backbone: Connect devices via T-connectors. Avoid star-shaped layouts where multiple backbones branch from a central point. • Keep Drop Cables Short: Adhere to the standard for your protocol (e.g., max 6m for NMEA 2000). The shorter, the better. • Ensure Good Connections: Use high-quality, protocol-approved connectors. Safiery’s CAN connectors and cabling is NMEA 2000 Approved. DONT splice wires directly. • Centralize Power: Insert 12V power near the middle of the backbone to ensure even voltage distribution to all devices. By following these fundamental wiring principles, you can create a robust and reliable CAN bus network that will perform as expected.
WWW.SAFIERY.COM
Powered by FlippingBook