No, Siemens and Square D breakers are not interchangeable. While both manufacturers produce circuit breakers that meet the same standards established by Underwriters Laboratories (UL), they are designed to fit different frames and load centers. Siemens plated lug style circuit breakers are designed for use with Siemens type panels or other compatible load centers, while Square D QO style load centers require QO series single pole or double pole type circuit breakers. The two companies also have differences in their technology which may cause compatibility issues if used together on the same system. For instance, a Siemens breaker would be incompatible with an electrical system using a Square D GFI device since it uses its own unique grounding mechanism not found on other brands of equipment. Therefore, it is important to always ensure that all components used in an electrical installation match the brand of panel being used so as to avoid any potential problems due to incompatibility between different types of devices.