Honeywell CADVR-04D User Manual page 234

Importance
For E (earth cable)
There is a shortcut way to check these thee cables connection are
standard or not (not the accurate check).
In the following operations, the multimeter range shall be at 750V!
Turn the digital multimeter to 750V AC, use your one hand to hold the
metal end, and then the other hand insert the pen to the E port of the
socket. See the following figure. If the multimeter shows 0, then you can
see current earth cable connection is standard. If the value is more
than 10, then you can see there is inductive current and the earth cable
connection is not proper.
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