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# UFC 3-520-01 Interior Electrical Systems

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UFC 3-520-01
June 10, 2002
B-4
temperature). The line current is calculated based on the expected real power
requirement and phase angle. The following equations show the calculation of line
current:

Single-Phase Circuits
cos
×
=
V
P
I
L
where,
I
L
= Line current in amperes
P
= Real power, in kW
V
= Voltage, RMS--in kV to match power units
?
= Phase angle between voltage and current

Three-Phase Circuits
cos
3
×
×
=
L
L
V
P
I
where,
I
L
= Line current in amperes
P
= Total three-phase real power, in kW
V
L
= Line voltage, RMS--in kV to match power units
?
= Phase angle between voltage and current

B-2.3
If comparing voltage drops across different nominal voltages, reference
voltage drop calculations to a 120 volt base to allow ready comparison of the voltage
drops throughout the system, regardless of the actual voltage level. Use the following
expression to convert a voltage drop at some nominal voltage to a 120 volt base:
Voltage
Nominal
System
Drop
Voltage
Actual
Base
V
Drop
Voltage
Actual
120
)
120
(
×
=
B-3
TRANSFORMER RATED CURRENT.

B-3.1
Transformer rated secondary current is calculated by dividing the rated kVA
capacity by the rated secondary voltage. The following examples illustrate the rated
secondary current calculation.

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Summary :

## = Phase angle between voltage and current B-2.3 If comparing voltage drops across different nominal voltages, reference voltage drop calculations to a 120 volt base to allow ready comparison of the voltage drops throughout the system, regardless of the actual voltage level.

Tags : current,power,line,rated,drop,120,secondary,phase,following,nominal,base,actual,real
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