Spectra RMS Molded Case Circuit Breakers (SE150, SF250, SG600 and SK1200) have a digital, solid state, RMS sensing trip system with field installable, front-mounted rating plugs to establish or change the breaker ampere rating. Adjustable instantaneous with tracking short-time is standard on all frames. The trip unit uses digital sampling to determine the RMS value of sinusoidal and non-sinusoidal currents.