33. GDT for 24VDC Industrial Field Wiring Surge Protection

Long 24VDC field cables running across factory floors and outdoor cable trays act as antennas for lightning-induced surges. These surges can damage the controller’s input circuitry, TVS diodes, and ICs.

A GDT at the controller input acts as primary (first-stage) protection. It absorbs the high-energy portion of the surge. A downstream TVS diode (second stage) then clamps any residual voltage to a level safe for the board components.

The 75V spark-over is well above the 24VDC supply range (up to 30V with tolerance), so the GDT stays inactive during normal operation.

Required: 75V Spark-Over · ≥5kA (8/20µs) · 2-Pole · Surface Mount · Littelfuse · RoHS

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 → Surface Mount
• Manufacturer → Littelfuse Inc.
• Part Status → Active

Tip: In a two-stage protection scheme, a decoupling element (usually a small inductor or resistor) between the GDT and TVS diode ensures proper energy coordination — the GDT fires first and handles the bulk energy, while the TVS handles the fast residual.

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

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