Understanding LS Electric Trip Units: OCR vs. STU

Over the years, LS Electric trip units have gone through several updates and revisions. As a result, there have been changes in both naming and product specifications.

LS Electric offers two main types of trip units:

• OCR (Overcurrent Relay) – This refers to our earlier generation of trip units.

• STU (Smart Trip Unit) – This is our latest, most advanced model, featuring enhanced technology and capabilities.

As we continue to update our products, many customers have questions about the differences between older and newer trip units—especially when ordering replacements or evaluating existing systems. To help with this, we've provided a conversion chart that shows how older OCR models correspond to the newer STU versions.

We frequently receive questions about legacy trip units like the AM1 and AX1, but we've also included information on other models. At the bottom of this guide, you'll find images outlining the technical specifications of the older OCR trip units for reference.

If you have any further questions about compatibility or specifications, feel free to reach out to us.