水雾喷淋系统探头自我检测功能中的earth fault

xychu

GL规范电气章节里对于火警探头以及水雾喷淋的火灾探头都有一个要求
The fire detection system shall be selfmonitored.
Faults, such as a supply failure, short circuit or
wire break in detection loops, the removal of a detector
from its base and earth fault in detection loops with
all-pole insulation shall be optically and audibly signalled
at the central fire alarm panel. Fault alarms
shall be acknowledgeable and, wherever possible,
distinguishable from a fire alarm.
请教下红色中的这个接地故障如何理解，是带两级隔离的探测回路才需要接地故障么？这个要求的初衷是什么？求各位解释下，顺便祝各位节日快乐。

gq_ee

本身就是all pole insulation，就是相与相、相与地之间绝缘
这句话可以忽略不计