A.后級短路時前、后級熔絲應(yīng)同時熔斷 B.前級先熔斷,后級起后備作用 C.后級先熔斷,以縮小停電范圍 D.后級先熔斷,前級1min后熔斷
A.30s B.45s C.60s D.90s
A.1m B.2m C.3m D.5m