GE Industrial Solutions Evolution Switchboards - Manuel (Page 8)

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Chapter 2- Installing the Switchboard
88
FFiigguurree 99.. Typical single-source ground-fault protection
using ground-fault relays.
FFiigguurree 1100. Typical single-source ground-fault protection
using integral ground-fault trips.
FFuussee SSeelleeccttiioonn
Select the proper fuses for each circuit based on load
characteristics and available short-circuit current at the line
terminals of the switchboard. Select a fuse for which the
rating of the combination fuse and switch equals or exceeds
the available short-circuit current. Removable link-type
fuses are not recommended.
TTeessttiinngg aanndd IInnssppeeccttiioonn
After the equipment has been installed and all connections
made, test and inspect the switchboard before energizing.
Although the equipment and devices have been inspected
at the factory, perform a final field test to be certain that the
equipment has been properly installed and that all
connections are correct and have not loosened during
transportation. Completely check the wires and all bolts and
terminals for tightness. Check all Kirk key interlocking
schemes to insure desired performance. Make sure that the
incoming line is de-energized while all tests are in progress.
In addition to these mechanical checks, use a
megohmmeter to test the switchboard. Open all
switchboard devices and remove all instrumentation and
control fuses. Use a megohmmeter developing 500 volts.
Switchboards tested when leaving the factory show typical
minimum values of 100 megohms. If any switchboard tested
under the above conditions shows resistance values
considerably below this, inspect it for possible tracking on
insulation or insulation breakdown.
All scraps of wire, plaster, dust, and other foreign material
must be removed. Vacuum cleaning is recommended for
cleaning.
After thorough cleaning and inspection, if the megohm
reading is still low, it may still be safe to energize the
equipment. When restoring flooded or wet equipment to
service, for example, the accepted practice is to require a
minimum of 1 megohm before energizing. Under damp or
humid conditions, it is considered good practice to operate
the equipment at lower-than-rated voltage for a short time,
if possible, to improve the low reading.
Instructions for inspection and testing of low-voltage power
circuit breakers are given in the applicable individual
instruction manuals. Directions for testing devices such as
relays, instruments, and meters are found in the instruction
manual furnished with each device. Protective relays must
be coordinated with other relays in the system; therefore,
these relays are set by the purchaser. General instructions
on setting relays are provided in the relay instruction
manuals.
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When ground-fault protection is provided, all field
connections must be made correctly to insure proper
functioning of the ground-fault protection system. Observe
the rules described in the following sections, as illustrated in
Figures 9 and 10.