45. GDT for RS-485 Bus Lightning Protection
1. Component Purpose
RS-485 cables running 500+ meters between buildings act as long antennas that pick up lightning-induced voltage surges. These surges can be thousands of volts — instantly destroying the RS-485 transceiver chip.
A GDT at each port entry absorbs this energy. The 75V spark-over is well above the RS-485 operating range (−7V to +12V), so it stays inactive during normal communication. Through-hole mounting provides robust mechanical connection for industrial environments.
Required: 75V Spark-Over · ≥5kA (8/20µs) · 2-Pole · Through Hole · Littelfuse · RoHS
2. How to Find It on DigiKey
Go to DigiKey.com → Circuit Protection → Gas Discharge Tube Arresters (GDT)
Apply these filters:
- Voltage - DC Spark Over (Nom) → 75V
- Impulse Discharge Current (8/20µs) → 5kA or higher
- Number of Poles → 2
- Mounting Type → Through Hole
- Manufacturer → Littelfuse Inc.
- Part Status → Active
Tip: A GDT alone provides primary protection for high-energy surges. For complete protection, pair the GDT with a downstream TVS diode to clamp residual voltage to a safe level for the transceiver.
3. Key Specifications & What They Mean
| Specification | Required | Why |
|---|---|---|
| Spark-Over Voltage | 75V | Well above RS-485 range; surge-only firing. |
| Surge Current | ≥5kA (8/20µs) | Handles lightning on 500m+ outdoor cables. |
| Number of Poles | 2 | Protects A and B lines in one package. |
| Mounting | Through Hole | Robust for industrial environments. |
| Manufacturer | Littelfuse | Company AVL requirement. |
| RoHS | Yes | Compliance required. |
4. Selecting a Safe, Production-Ready Part
The filtered list will show matching parts. Before you pick one, check: Is it Active? Is stock available? Is the manufacturer reputable? Is a datasheet available?
Full checklist: How to Select a Safe, Production-Ready Component — EWskills Guide