Honeywell CADVR-04D User Manual page 233

When considering the earthing, you need to think about two aspects:
The first is the system compatibility, and the other is the external
interference coupling into the earth circuit, which results in system error.
For the external interference is not regular, it is not easy to resolve.
3. Thunder proof ground method in the monitor system
The monitor system shall have sound thunder proof earthing to
guarantee personnel safety and device safety.
The monitor system working ground resistance shall be less than 1Ω.
The thunder proof ground shall adopt the special ground cable from the
monitor control room to the ground object. The ground cable adopts
copper insulation cable or wire and its ground section shall be more
than 20mm2.
The ground cable of the monitor system can not short circuit or mixed
connected with the strong alternative current cable.
For all the ground cables from the control room to the monitor system or
ground cable of other monitor devices, please use the copper
resistance soft cable and its section shall be more than 4mm2.
The monitor system usually can adopt the one-point ground.
Please connect the ground end of 3-pin socket in the monitor system to
the ground port of the system (protection ground cable)
4. The shortcut way to check the electric system using the
digital multimeter
For 220V AC socket, from the top to the bottom, E (ground cable), N
(neutral cable), L(live cable). Please refer to the following figure.
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