2 sentences for 断开 (duàn​kāi — turn off)

1. 在更换灯管之前，请务必先断开电源。

   zài gēng​huàn dēng​guǎn zhī​qián, qǐng wù​bì xiān duàn​kāi diàn​yuán.

   Be sure to disconnect the power supply before replacing the lamp tube.

   Source: Dong Chinese Dictionary

2. 如果电路中有一处断开，就会形成开路，灯泡也就不会亮。

   rú​guǒ diàn​lù zhōng yǒu yī chù duàn​kāi, jiù huì xíng​chéng kāi​lù, dēng​pào yě jiù bù huì liàng.

   If there is a break in the circuit, it will create an open circuit, and the light bulb will not light up.

   Source: Dong Chinese Dictionary