
SEBU8219-01 37
Product Information Section
Product Identification Information
Grounding the Frame
In any generator set installation, the frame of the
generator must be positively connected to an
earth ground. This connection should be the first
connection that is made during installation. This
connection should be the last connection that is
removed. The ground connection must be flexible in
order to avoid breakage during operation.
Ground connection cable or straps should have at
least the current carrying capacity of the largest
line lead to the connected load. Joints in cables or
straps must be clean, free of electrical resistance,
and protected from possible oxidation. Bolted ground
connection joints eventually oxidize. The joints are
frequent sources of radio frequency interference
(RFI). Bolted connections should be silver soldered
for the best performance.
Neutral Connections
Generators with grounded configurations usually
have a neutral that is grounded when the generator
is installed. Ground the neutral in order to prevent
equipment damage and personal injury.
If the neutral wire is grounded and one of the phase
leads becomes grounded, the excessive current will
open a load circuit breaker in order to isolate the
fault. If the circuit breaker does not open, then the
excessive current will reduce the generator voltage
to zero. The result depends on the characteristics of
the generator, the type of fault, and the trip rating of
the circuit breaker. An undervoltage device may be
required in order to provide an adequate short circuit
protection.
Some installations do not require the neutral wire
to be grounded. Ungrounded neutral leads are
acceptable if measures have been taken in order to
prevent grounds to the phase leads. An example of
such measures are ground fault protective circuits.
All of the distribution circuits must be treated as a
system in order to ensure ground fault protection.
The operator should contact a certified and registered
consultant if a new distribution system is being
developed. The owner should also engage a certified
and registered consultant if an existing system should
be modified for the ground fault protection.
Neutral resistors and reactors may be added to the
system for two reasons: to provide protection during
faults and to limit neutral currents.
Single Units
In a three-phase, four-wire system, the neutral wire
should be grounded according to local wiring codes.
In application
swheredefinite measures are taken
in order to prevent grounds to the load leads, an
ungrounded neutral can be used. Be sure to check
your local wir
ing codes.
Multiple Unit
s
Operation of multiple generators in parallel, having
all neutrals
grounded, may result in the circulating
current through the neutral connections. In order
to eliminate the possibility of circulating currents,
ground the ne
utral of only one generator. If multiple
generators are alternated on line, a switch should
be installed in the neutral ground circuit of each
generator.
In this case all neutral ground circuits
except one can be opened. Be sure that one of the
neutral ground circuits is closed.
Parallel to Utility
When a Wye (Star) connected generator is going
to operate in parallel with a utility system (infinite
bus) and wh
en the secondary of the step-down
transformer in the utility system is also a Wye
connection, the following may happen. The grounding
of both Wye
neutrals may result in circulating currents
through the neutrals. Also, the coordination of ground
fault protection requires an entire system study. A
study sho
uld be done by a certified and registered
consultant who is familiar with generator systems.
The study will determine which grounding method
should be
used.
i01553111
Generat
or Lead Connection s
SMCS Code: 4450
Lead Numbering
The Wye Configurations and the Delta Configurations
are the most common generator lead connections.
The foll
owing three-phase connection diagrams
illustrate the proper connection and lead identification.
The lead
s are numbered clockwise from the top
and from the outside inward. The diagrams that
are contained in the “Wye Configuration Diagrams”
sectio
n show lead numbering for the six lead
generators and for the twelve lead generators. The
diagrams contained in the “Delta Configuration
Diagra
ms” section show lead numbering for the six
lead generators and for the twelve lead generators.