GDT for RS-485 Bus Lightning Protection

Question

Problem: GDT for RS-485 Bus Lightning Protection. Solve this hands-on electronics task on EWskills.

Accepted Answer

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

5. Filtered DigiKey Link

➡ View Matching Parts — Littelfuse, GDT, 75V, ≥5kA, 2-Pole, Through Hole

45. GDT for RS-485 Bus Lightning Protection