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.