44. GDT for Ethernet Port Lightning Protection
1. Component Purpose
Outdoor Ethernet cables to IP cameras are exposed to lightning. A surge on the cable pairs can destroy the Ethernet PHY chip and PoE circuitry, which are very sensitive semiconductors.
A GDT placed on each cable pair at the port entry absorbs the high-energy surge before it reaches the board. The 75V spark-over is above the maximum PoE voltage (57V per IEEE 802.3af/at), so the GDT stays inactive during normal PoE operation.
Outdoor Ethernet requires ≥10kA surge rating because the cable runs can be long and directly exposed to lightning-induced currents.
Required: 75V Spark-Over · ≥10kA (8/20µs) · 2-Pole · Surface Mount · 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) → 10kA or higher
- Number of Poles → 2
- Mounting Type → Surface Mount
- Manufacturer → Littelfuse Inc.
- Part Status → Active
Tip: Each Ethernet port has 4 cable pairs. You need one 2-pole GDT per pair. The user selects the correct single GDT component; the BOM quantity depends on the number of pairs to protect.
3. Key Specifications & What They Mean
| Specification | Required | Why |
|---|---|---|
| Spark-Over Voltage | 75V | Above PoE max (57V); fires only on surges. |
| Surge Current | ≥10kA (8/20µs) | Outdoor cables need heavy surge handling. |
| Number of Poles | 2 | Protects one cable pair per GDT. |
| Mounting | Surface Mount | Compact for Ethernet port PCB layout. |
| 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