back-up breaker

例句：

1. 1.The power company installed a backup generator to ensure continuous power supply during an emergency.
   电力公司安装了一台备用发电机，以确保在紧急情况下持续供电。
2. 2. During the power outage, the back-up breaker automatically switched on, providing light and heat for the house.
   在停电期间，备用断路器自动启动，为房屋提供照明和暖气。
3. 3.The engineer tested the back-up breaker to ensure it worked properly before starting the project.
   工程师测试了备用断路器，确保其正常工作后才开始项目。