UFC 3 -520-01
June 10, 2002
Figure B -3. Overduty Molded Case Circuit Breakers
Utility
Service Bus
MCC Bus
-7%
33%
33%
33%
M
M
M
Motor 1
Motor 2
Motor 3
B-2
VOLTAGE DROP .
B-2.1
Calculate voltage drop by the following equation:
Voltage Drop = IL (R cos θ + X sinθ )
where,
IL
=
Line current in amperes
R
=
Resistance of line in ohms
X
=
Reactance of line in ohms
?
=
Phase angle between voltage and current if phase angle
is not known, assume a phase angle of 36.9 degrees
corresponding to a power factor of 0.8.
B-2.2
The above equation is simplified, but usually provides acceptable results. In
the above equation, obtain the conductor resistance and reactance values as a function
of gauge size from NEC Chapter 9, Tables 8 and 9 (2002 Edition). Note that NEC
conductor resistance values are based on 75 C (167 F) and will usually require
correction to the actual expected temperature (refer to NEC Chapter 9, Tab le 8, or the
first example in paragraph B -6.1 for how to convert the resistance to a different
B-3
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