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(1) The measurement of the grounding resistance of machine
room in the building
The machine room of telecommunication system normally in the
upper deck of the building, and it hard to use the megohm meter to
measure. However, it is very convenient to for ETCR. Connect the
fire hydrant and the pole being measured by one testing line, then
use the meter test the testing line.
The value of meter=resistance of machine room + the resistance of
testing line + the grounding resistance of fire hydrant. If the groun-
ding resistance of fire hydrant is very small, then: the grounding
resistance of machine room
≈value of meter-resistance of testing
line
(2)The measurement of grounding resistance of machine room
and the launch tower
It normally form two point grounding system When machine
room and launch tower connect to ground, as show below:
If the value of meter is lower than the allowable value of grounding
resistance, then the grounding resistance of machine room and the
launch tower is valid. If the value is greater than allowable value,
please measure by single point grounding method.
3. Application in lightning protection system of building