Type TH heavy duty safety switches are designed for commercial and industrial applications where safety, high performance and continuity of service are essential. When used with Class R or J fuses, 30-600 amp switches have a UL Listed short-circuit rating of 200,000 rms symmetrical amps. Switches rated 800-1200 amps use Class L fuses and have a UL Listed short circuit rating of 100,000 rms symmetrical amps.