GROUNDING
TESTING AND ADJUSTING
3. There have been reports of excessive circulating
neutral current occurring when two or more
generators are operated in parallel. Generators
should be installed with the assumption that no
excessive circulating neutral current will occur with
the generators paralleled at full load. The phase
current should not exceed 100% of the generator
nameplate ampere rating.
In those cases where excessive neutral currents are
encountered, either a neutral lead reactor or
selective grounding of the neutrals may be used. If
selective grounding of one generator neutral is used,
a disconnect switch should be installed in each
generator ground lead. The disconnect switch
should have about 25% more current carrying
capacity than the generator line ampere rating.
NOTE: Three phase, "Y"-connected
generators can have a third harmonic
voltage that does not cancel at the
neutral. It is this voltage that causes
the
excessive
circulating
neutral
current
that
can
occur
when
operating in parallel.
4. Instructions concerning excessive neutral current
and grounding the generator neutral also apply to
former model generators.
5. Most radio and audio frequency interference
problems are corrected by proper grounding of the
generator frame. In other instances, the cause is
not the generator set, but equipment that may be
related or unrelated to it. A small, hand-held battery-
powered radio is a useful tool in locating the source
of interference. Tune the radio receiver to the
frequency of the interference and use the receiver
as a probe around pipes, conduits, or other metal
parts. Emitted noise will increase as the source is
approached. Pipes rubbing together can cause
radio frequency interference. Instances have been
known where steel and galvanized pipe connections
create interference even though the joint is
mechanically sound and leak proof. In areas
adjacent
to
high
power
radio
frequency
generators(transmitters, heating equipment, etc.), a
partial or corroded joint or connection acts like a
very poor rectifier, and can emit interference at
frequencies different from the exciting frequency.
The solution in all such instances has been physical
bonding of the joint or conduit. A clean copper strap
bridging the joint normally clears up the interference.
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