Amp-Trap® A™ R fast-acting fuses are the smallest dimension 600 V fuses suitable for branch-circuit protection. The A™ R is a popular choice for economical protection of control circuits and control circuit transformers where available short circuit currents exceed 10,000 amperes. A™ R's rejection dimensions prevent substitution by lesser rated fuses. These fast-acting fuses give current-limiting protection to general circuits.