故障指示器汇集单元电源回路与外壳,额定绝缘电压Ui≤60V 时,施加500V/1min 工频电压应无击穿、无闪络( )( )
A.A-250V/1min
B.B-500V/1min
C.C-1000V/1min
D.D-2000V/1min
正确答案是B