You're right, finding TCC curves for those older Square D ML circuit breakers can be tough. They are definitely obsolete, and Square D doesn't readily provide that information anymore.Here's a breakdown of how to approach getting the TCC curves, along with some things to consider

1. Search for Existing Documents (Even More Scrappy Search):
Online Archives and Forums

Dig even deeper into online archives. Try searching on these lines: "Square D ML circuit breaker catalog" "Square D ML breaker time-current curve" "Square D MOL circuit breaker datasheet" "Square D MOL breaker trip curve" "Obsolete Square D breaker data" "Square D ML breaker ETAP model" - someone may have already done the work!

Used Equipment Dealers

Sometimes used equipment dealers that specialize in older electrical gear might have catalogs or data sheets they've accumulated.

Electrical Engineering Forums (Again!)

Post on forums like: Eng-Tips (Electrical Engineering) IEEE forums (if you have access) Other specialized electrical engineering groups on LinkedIn.

2. Contact Square D (Schneider Electric) - Still Worth a Try



Schneider Electric Technical Support

Contact Schneider Electric (Square D) technical support, specifically mentioning that you're trying to model an existing installation using obsolete ML breakers and need the TCC curves for safety coordination. Explain the situation fully. Sometimes, even if the documentation isn't readily available, they might have it in an archive somewhere. Be polite and emphasize the importance of the information for safety and proper system modeling.

Local Square D Distributor

A long-shot, but a very experienced local Square D distributor (the kind that's been around for decades) might have access to old data or know someone who does.

3. Generic Breaker Approximation (Least Desirable, but Sometimes Necessary)



NEMA Standard MCCB Curves

If you absolutely cannot find the specific curves, you might be able to use generic TCC curves for molded case circuit breakers (MCCBs) that meet NEMA standards. This is not ideal because the trip characteristics can vary significantly between manufacturers and even different series from the same manufacturer. However, it's better than nothing for a first-pass approximation. Look for generic MCCB curves that are rated for similar voltage, current, and interrupting capacity.

Consult an Experienced Protection Engineer

Crucially, if you go this route, consult with a protection engineer who has experience with older electrical systems. They can help you select the most appropriate generic curves and understand the limitations of this approach.

4. Important Considerations and Warnings



Age and Condition

Remember that the breakers are old. Their actual trip characteristics may have drifted over time due to aging components, environmental factors, and previous overcurrent events. The TCC curves you find might not perfectly represent the breaker's current behavior. Testing the breakers is vital for accurate modeling

Testing

Ideally, you should have the existing breakers tested by a qualified electrical testing company. They can perform primary injection testing to determine the actual trip characteristics. This is the most reliable way to get accurate data for modeling.

Coordination Study

Before making any changes to the system, perform a thorough coordination study using the best available TCC data. This will help ensure that the breakers are properly coordinated to protect the electrical system and prevent nuisance tripping.

Documentation

Document everything you do – the source of the TCC curves, the assumptions you made, and the results of any testing. This is essential for future reference and maintenance.

Key Takeaway:

Finding the exact TCC curves for those old Square D ML breakers will be challenging. Start with thorough online searching, contact Square D and used equipment dealers, and consider contacting a testing company. If all else fails, you might be able to use generic MCCB curves as a starting point, but only with the guidance of an experienced protection engineer and awareness of the limitations. Testing the breakers is highly recommended for accurate modeling.Good luck with your search! Let me know if you find anything! Flag for review