Karel DS200, Техническое справочное и монтажное руководство

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DS Series PBX Technical Reference And Installation Guide
115
XI.1.D. GROUND CONNECTION:
Good grounding is mandatory in order to protect an exchange of the DS200 series from
thunderbolts and other high voltage effects that might induce over lines or peripheral devices,
or noise created by external devices.
The 230 VAC power cord of the exchange has grounding feature, so there is no need for an
extra grounding if the electric installation of the building has sound grounding. However,
soundness of the electric installation must be verified through measurements. (See section
I.1.D.1)
Although special tools are required for measuring the sufficiency of grounding of the electric
installation of the building precisely, voltages between Neuter-Phase and Neuter-Ground can
be measured for getting an idea. The Neuter-Phase voltage should be 180-260 VAC and the
Neuter-Ground voltage should be 1-2 VAC. Those values must be consistent. Possible
voltage leakage in grounding installation may damage your exchange, just like all other
devices that require grounding
*
ADDITIONAL GROUNDING MUST BE PROVIDED, IF SOUNDNESS OF THE
GROUNDING OF THE ELECTRIC SYSTEM CANNOT BE GUARANTEED.
Water installation of the building can be used for grounding, provided that the pipes are of
metal and no insulation material has been applied at junctions. However, if those installations
are to be used, one must make sure that no living or inanimate creature could come into
touch with any point on those installations, as long as the human and environmental safety is
concerned.
Indeed, the safest grounding method is inserting a copper rod that is 1.5 cm in diameter with
a length of 1.5 m. into the ground and connecting it to the exchange over a copper grounding
cable. A copper plate may be used as an alternative to the copper rods.
In order to ensure safe grounding, it is recommended that at least three copper rods or a
copper plate be employed.
For the case where copper rod is employed, after three pits that are 50 cm. in diameter and
approximately 30 cm. deep are dug at least 2 m. apart from each other, copper rods whose
length is 1,5 m. are driven into those pits so deeply that segments of 15-20 cm. stick out of
the ground. Then, the three rods are connected to each other with a copper cable whose
cross sectional area is 16 mm
2
and with connection clips attached to the top of the copper
rods. A connection is made with the same copper cable to the ground connection point of the
exchange, from the closest copper rod to the building. After all the connections have been
completed, the copper rods are driven down to the bottom of the pits. Applying some grease
onto the clip connections would prevent corrosion that might occur in the future. As for the
cables that have remained on the ground surface, they are placed in a channel dug among
the pits and then covered with soil. After applying some grease onto the copper rods as well,
rock salt and carbon powder are poured upon them and the conductivity is increased by
finally adding water. In order to measure the completed grounding, the MEGER device
should be used, as much as possible. This device is used to measure grounding only. In
case the Meger device is not available, the potential difference between the NEUTER and
GROUND cables are supposed to be measured with a standard voltmeter as a value which
is close to zero. Finally, the grounding work is completed by covering all pits.
The illustration below shows how the grounding operation is carried out.