Powell FlexGear, Инструкционный бюллетень

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18 Installation
01.4IB.26264A FlexGear
™
Low Voltage Arc Resistant Switchgear
G. G
roundInG
Before power connections can be made, the
switchgear vertical sections must be grounded.
A ground bus is furnished with lugs at each
end for connection to the station grounding
system.
A permanent low-resistance ground is
essential for adequate protection. Improperly
grounded equipment may result in death,
bodily injury or property damage.
!
WARNING
The ground bus is bolted to the rear of the
vertical section near the bottom. It is arranged
so that connections to the station ground can
be made in any unit.
Where equipment is shipped in more than one
group, the sections of ground bus must be
connected by using the splice plates furnished
with the equipment (Figure 7) . Assemble the
ground bus joints as outlined under
Ch 4 Installation, H. Connections . Ground bus
connections are made in the lower portion
of the cable entrance compartment. The
switchgear ground bus must be connected to
the station ground bus by a conductor having
a current carrying capacity equal to that of the
switchgear ground bus. It is very important
that the equipment be adequately grounded
to protect the operator from injury when short
circuits or other abnormal occurrences take
place and to ensure that all non-live parts of
the equipment are ground potential.
It is recommended that the connection to the
station ground have a cross section of 500,000
circular mils (240mm
2
) or greater if the soil
in which it is buried is of such character as to
cause appreciable corrosion. This is especially
true where electrolysis from stray currents
or contact with dissimilar metals exists. The
resistance of the soil surrounding a station
ground depends on the condition of the soil as
well as its chemical content. Dry, loose, sandy
or frozen soils will have a high resistance as
compared with moist soils or soils containing
ashes, cinders or salt solutions. IEEE Standard
142 states that grounding impedance in the
range of 1 to 5 ohms is generally acceptable
for industrial substations. Ground resistance
testing is recommended to verify that the
ground resistance falls within this range.
H. c
onnectIonS
The main bus bars and other connection bars
are copper. The connection surfaces are silver
surfaced or equivalent. The silver plating used
on bolted contact surfaces is approximately
0.0001” thick. All field assembled joints in
primary conductors, regardless of method of
insulation, should be made as follows:
1. Wipe the surface clean with a lint-free cloth.
Do not use sandpaper or any other abrasive
material on the plated surface. Avoid
handling of cleaned surfaces as much as
possible. If the surface is tarnished, clean
it with silver polish and then wash it with
denatured alcohol.
2. Join the clean contact surfaces by using the
hardware provided.
The correct length of bolt must be used
in each joint to ensure that electrical
clearances at bolt locations are maintained.
As a general rule, when using ½ inch
diameter bolts, the bolts should be 1 inch
longer than the combined thickness of the
copper bars being bolted together.