46. MOV for 24VDC Industrial Bus Surge Protection

On a factory floor, the 24VDC bus shares cable trays with motor power cables, solenoid drivers, and VFDs. These generate fast voltage spikes (transients) that travel along the 24V bus and can damage sensitive sensor interfaces and MCU inputs.

An MOV across the 24V input clamps these transient spikes. The critical design decision is choosing the right MOV voltage rating:

• Too low (≤30V): the MOV may conduct during normal 24V operation (which can reach ~26.4V with +10% tolerance), leading to overheating and failure.
• Too high (≥43V): the clamping voltage is so high that the “clamped” surge still damages 24V-rated components.
• Correct (31V–43V): stays inactive during normal operation, clamps transients to a safe level.

Required: 31V–43V DC · ≥2kA surge · ≥20J · 1-Circuit · Disc · Through Hole · Littelfuse · RoHS

Go to DigiKey.com → Circuit Protection → Varistors, MOVs

Apply these filters:

• Maximum DC Volts → 31V to 43V range (select available values: 31V, 36V, 39V, or 43V)
• Current - Surge → 2kA or higher
• Energy → 20J or higher
• Number of Circuits → 1
• Mounting Type → Through Hole
• Package / Case → Disc
• Manufacturer → Littelfuse Inc.
• Part Status → Active

Tip:  For DC applications, check the "Maximum DC Volts" column on DigiKey, not "Maximum AC Volts." The DC and AC ratings are different for the same MOV.

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, MOV, 31–43VDC, ≥2kA, ≥20J, Disc