GE EntelliGuard G Application Manual page 54

Section 6. Application Data
Ambient temperature always refers to the temper-
ature of the air immediately surrounding the
breaker and not the temperature of the air outside
the breaker's enclosure. Room or outside air tem-
peratures only establish the thermal floor to which
all other heating is added.
To convert breaker ambient from room ambient, it
is necessary to know the temperature rise within
the equipment housing the breaker. Temperature
rise is a function of several variables, including
heating caused by other equipment, ventilation,
solar heating, factors relating to group mounting
and the free surface area of the breaker's enclosure.
Once the device's ambient temperature is deter-
mined, select Factor B from Table 6.4.
Operating Frequency – Factor "C"
All UL EntelliGuard circuit breakers may be applied
at their published ratings on 50 Hz and 60 Hz
power systems. At nominal system frequencies
less than 50 Hz but above direct current, digital
solid-state trip may become inaccurate. On direct
current systems, digital solid-state trip units are
completely inoperative. EntelliGuard G circuit
breakers may be used on DC applications, but
EntelliGuard TU trip units may not.
System operating frequencies above 60 Hz may
change the performance and ratings of circuit
breakers by heating metallic parts and significant-
ly reducing interrupting capacity. EntelliGuard TU
trip units are not suitable for applications at 400Hz.
For operating frequencies of both 50 Hz and 60
Hz, the operating frequency rating Factor "C" =
1.00. For operating frequencies other than 50 Hz
and 60 Hz, contact your GE applications engineer.
Altitude – Factor "D"
EntelliGuard G UL circuit breakers are designed for
operation at altitudes from sea level to 6000 feet
(1800 meters). Reduced air densities at altitudes
above 6000 feet affect the ability of the circuit
breaker to both transfer heat and interrupt short
circuits. Determine the altitude of the breaker's
installation, and select the altitude rating-factor
"D" from Table 6.5.
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Load Class Rating – Factor "E"
The type of load and its duty cycle must be con-
sidered in the application of EntelliGuard G circuit
breakers. Loads such as capacitors and electro-
magnets require a substantial and continuous
de-rating factor if the breaker is normally used to
switch the load. With loads such as resistance
welders, the breaker's continuous current rating
must be no less than 125% of the welder's 100%
duty-cycle rating.
In general, circuit breakers are intended for the
protection of insulated cable. Where a circuit breaker
is intended to protect load equipment, prudent
engineering practices call for obtaining factory review
and concurrence with the selection of a specific
protective device. Load class selection Factor "E"
for typical application are listed in Table 6.6.
Safety – Factor "F"
A safety factor is used to provide a design margin
between the rating of a circuit breaker and the
derived operating current using all of the applica-
ble selection factors. A safety factor of at least
10% is often used to ensure the circuit breaker is
adequately sized. In addition it may be useful to
consider future growth.
Other Factors that Influence Circuit Breaker Sizing
100% vs. 80% Ratings: All EntelliGuard G circuit
breakers are 100% rated except for the 6000A
stationary mounted UL 489 circuit breaker. Circuit
breakers that are 100% rated are not required to
be sized at 125% of the expected load. However, it
is recommended that a safety factor, as described
above, always be considered when selecting over-
current device sizes.
An important consideration may be the circuit
breaker's desired selective and protection perform-
ance within the context of the system where it is
installed. Certain settings are functions of the trip
plugs, others of the sensors. In Table 3.11 you will find
the sensors available on a per frame basis. Table
3.9 identifies the trip rating plugs available for each
sensor. Table 6.7 identifies the relationship between
specific circuit breakers and trip parameters.