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What is the difference between a Class CTL and Non-Class CTL load center?

Issue:
Product Design feature

Product Line:
QO load centers

Environment:
National Electrical Code 

Cause:
Application

Resolution:
Non-Class CTL (Circuit Limiting) load centers do not have a rejection feature that would restrict the number of tandem breakers that can be installed into them.  As a result, the load center could be overloaded.  A code change corrected this for safety reasons and all load centers (since approximately 1965) must be designed to meet CTL standards.  Load centers that are not designed to take tandem breakers have a rejection feature to prevent them being installed.
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