UFC 3-520-01
June 10, 2002
B-8
Input Data
#3/0 AWG
#4/0 AWG
Conduit size
51 mm (2 inch)
51 mm (2 inch)
Conductor resistance (30 °C)
0.0164
0.0130
Estimated power loss (3 phase) 673 W
534 W
Estimated wire cost
$991
$1,232
Estimated conduit cost
$365
$365
Incremental cost
$241
Projected energy savings
609 kWh/year
Cost savings at $0.08 per kWh
$48.72/year
Payback period
5 year
In the above example, the copper conductor resistance was obtained from NEC
Chapter 9, Table 8 (2002 Edition), and corrected for use at 30 °C (rather tha n
75 °C as listed in the table) in accordance with the following expression provided
by a footnote in the same table:
(
)
[
]
75
00323
.
0
1
1
2
-
×
+
×
=
T
R
R
, where R
1
is the copper conductor
resistance at 75 °C.
The estimated power loss was then calculated by:
R
I
Loss
Power
×
=
2
EXAMPLE: A single-phase, 15 ampere lighting load operates only 50 hours per
week (2,600 hours per year) and is located 30.5 meters (100 feet) from the load
center. As shown below, the larger #10 AWG conductor pays for itself in just
over 1 year. Thereafter, the installation continues to save energy costs of almost
$6 per year compared to the smaller #12 AWG conductor.
Input Data
#12 AWG
#10 AWG
Conduit size
12.7 mm (0.5 inch) 12.7 mm (0.5 inch)
Conductor resistance (30 °C)
0.3384
0.2120
Estimated power loss (1 phase) 76 W
48 W
Estimated wire cost
$12
$19
Estimated conduit cost
$42
$42
Incremental cost
$7
Projected energy savings
73 kWh/year
Cost savings at $0.08 per kWh
$5.8/year
Payback period
1.2 year
Summary :
UFC 3-520-01 June 10, 2002 B-8 Input Data #3/0 AWG #4/0 AWG Conduit size 51 mm (2 inch) 51 mm (2 inch) Conductor resistance (30 °C) 0.0164 0.0130 Estimated power loss (3 phase) 673 W 534 W Estimated wire cost $991 $1,232 Estimated conduit cost $365 $365 Incremental cost $241 Projected energy savings 609 kWh/year Cost savings at $0.08 per kWh $48.72/year Payback period 5 year In the above example, the copper conductor resistance was obtained from NEC Chapter 9, Table 8 (2002 Edition), and corrected for use at 30 °C (rather tha n 75 °C as listed in the table) in accordance with the following expression provided by a footnote in the same table: ( ) [ ] 75 00323 .
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cost,estimated,awg,conductor,year,per,power,saings,conduit,resistance,loss,inch,table