Yes, your interpretation is correct. Square D QO panels are often advertised with a "20 spaces, 24 circuits" rating, and the asterisk refers to the possibility of expanding to 24 circuits using specific "non-CTL" breakers.Here's a breakdown of why this might seem odd and what's happening: CTL Breakers (Circuit Total Limiting)

CTL is a system designed to prevent overfilling a panelboard. It limits the number of circuits you can install in a panel, ensuring the panel's load capacity isn't exceeded. CTL breakers have physical features (like a notch or tab) that work in conjunction with the panel's busbar to limit the number of circuits. Modern panels are required to be CTL.

Non-CTL Breakers

These breakers don't have the CTL features. They fit into the panel spaces but don't adhere to the CTL limitations. In the context of the QO panel, these are typically tandem (or "piggyback") breakers. These breakers allow you to put two circuits in a single breaker space.

Why It Seems Odd

The idea of recommending non-CTL breakers in a modern panel seems counterintuitive because it bypasses a safety feature designed to prevent overloading.

Why Square D Does This (Historically)

Square D QO panels have a long history and were popular before CTL regulations became widespread. Many older QO panels were designed to accept tandem breakers, which essentially offered more circuits in the same number of spaces.

Important Considerations



Load Calculation is Crucial

Even if you use non-CTL breakers, you must perform a proper load calculation for your electrical system to ensure you are not overloading the panel or any individual circuits.

Local Codes

Always check with your local electrical codes and inspector before using non-CTL breakers to expand the number of circuits in your panel. Some jurisdictions may prohibit or restrict their use, even in panels that technically accept them.

Panel Rating

Ensure that you never exceed the panel's overall amperage rating, even if you add circuits with tandem breakers.

Breaker Compatibility

Make sure that the tandem breakers you use are specifically designed and approved for use in Square D QO panels.In summary, while Square D's literature may mention the possibility of using non-CTL breakers to expand circuit count in some QO panels, it is essential to understand the risks, perform accurate load calculations, and adhere to all applicable electrical codes before doing so. Using non-CTL breakers to increase the number of circuits beyond the intended design of the panel can potentially overload the electrical system if it is not properly calculated and installed.

When in doubt, consult with a qualified electrician. Flag for review