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# UFC 3-520-01 Interior Electrical Systems

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UFC 3-520-01
June 10, 2002
B-3
Figure B-3. Overduty Molded Case Circuit Breakers
-7%
M
33%
M
33%
M
33%
Utility
Service Bus
Transformer
MCC Bus
Motor 3
Motor 2
Motor 1
B-2
VOLTAGE DROP.

B-2.1
Calculate voltage drop by the following equation:
(
)
sin
cos
X
R
I
Drop
Voltage
L
+
×
=

where,
I
L
= 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, Table 8, or the
first example in paragraph B-6.1 for how to convert the resistance to a different

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Summary :

## B-2.1 Calculate voltage drop by the following equation: ( ) sin cos X R I Drop Voltage L + × = where, I L = Line current in amperes R = Resistance of line in ohms X = Reactance of line in ohms ?

Tags : resistance,oltage,angle,motor,phase,nec,equation,drop,line,chapter,alues,usually,reactance
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