IMPEDANCE
Basic AC Reactive Components
where
ZT = total impedance (W)
VT = total voltage (V)
IT
= total current (A)
Total current in a parallel R-C-L circuit is equal to the square root of the sum of the squares of
the current flows through the resistance, inductive reactance, and capacitive reactance branches
of the circuit. Equations (8-15) and (8-16) are the mathematical representations of total current
in a parallel R-C-L circuit. Because the difference between IL and IC is squared, the order in
which the quantities are subtracted does not affect the answer.
IT =
(8-15)
I2R
(IC
IL)2
IT =
(8-16)
I2R
(IL
IC)2
where
IT
= total current (A)
IR
= current through resistance leg of circuit (A)
IC
= current through capacitive reactance leg of circuit (A)
IL
= current through inductive reactance leg of circuit (A)
Example:
A 200 W resistor, a 100 W XL, and an 80 W XC are placed in parallel across a
120V AC source (Figure 10). Find: (1) the branch currents, (2) the total current,
and (3) the impedance.
Figure 10 Simple Parallel R-C-L Circuit
ES-08
Page 16
Rev. 0
