One Wire Size Up Means Big Savings
Installing wire only one size
larger than has been required by the National Electrical Code
increases energy efficiency with dramatic paybacks.* This simple
technique can yield quick paybacks while increasing the flexibility of
the installation. By increasing the wire size, reduced power losses
offset the cost of the wire and produce savings on energy costs.
Why is this important?
By upsizing wire in a new installation, the engineer or contractor can
demonstrate the real savings to the customer as well as the advantages
of lower generated heat and increased flexibility of the installation.
In addition, when less heat is generated the result is reduced energy
requirements for fans and air conditioning systems.
Of course, there are many factors that must be considered in any
installation. But for most new applications, where the cost of labor
and conduit for the installation outweigh the cost of wire, the
increased size of the wire can pay for itself in less than two years.
At the same time, increased wire size is insurance against changing
future needs and assures lower voltage drops. Some companies, as a
matter of course, specify wire two or three sizes larger than minimum
requirements in neutrals, which are often overloaded due to harmonics.
Key elements that affect the payback, and thus the economic
incentive, to install larger wire gage, are the duty cycle, load
factor and electricity price. When using the same size conduit, the
increased cost of wire is minimal. As the examples below demonstrate,
the payback for upsizing can be quite short, even in single phase
lighting circuits, or one to two shift commercial settings.
How important is this to the
owner? Jim Clarkson, former Corporate Energy Manager of
Southwire Company, which has nearly 50 acres of industrial facilities
under roof in nine states, requires that all loads under 100 A shall
use wire one size larger than that required by code. "Quick
payback is assured under these circumstances," says Clarkson.
"Larger size applications are evaluated on a case by case
basis."
A simple way
to understand the dramatic impact of wire size on energy efficiency and
costs is to examine the number in these examples, in which one wire size
above code minimum is installed. All three examples include a separate
full-size grounding conductor, following current recommended practice,
and use THHN copper conductors.
Example
1
A three-phase circuit feeding a 125 H.P. 460 V motor, operating
at 75% load, 250 ft. from the load center, running 8,000 hours
per year. Draw is assumed to be 75% of 156 full-load amps (FLA). |
|
3/0 wire |
4/0 wire |
| Conduit Size |
2 in. |
2 in. |
| Estimated Loss (at 75% load and 44°C and 40°C,respective
conductor temps.) |
708 W |
554 W |
| Wire Cost |
$991 |
$1232 |
| Conduit Cost |
$365 |
$365 |
| Incremental Cost |
|
$241 |
| Energy Savings: at 75% load |
|
1,237 kWh/year |
Dollar Savings: at $0.07 per kWh
Payback |
|
$86.59/year
2 years, 9 months |
Dollar Savings: at $0.10 per kWh
Payback |
|
$123.70/year
1 year, 11 months |
In this
example, the payback is under 3 years,
and the savings continue indefinitely into the future. |
Example
2
The same I2R savings and short
paybacks apply to single-phase systems also. Take the case of a
single-phase, 15 amp lighting load operating continuously. To
simplify, assume the load is concentrated 100 ft. from the
panel. |
|
#12 AWG |
#10 AWG |
| Conduit Size |
1/2 in. |
1/2 in. |
| Estimated Loss (at 15 amp load and 40°C,
and 37°C,respective conductor temps.) |
77 W |
48 W |
| Wire Cost |
$11.82 |
$18.57 |
| Conduit Cost |
$42.00 |
$42.00 |
| Incremental Cost |
|
$6.75 |
| Energy Savings |
|
254 kWh/year |
Dollar Savings: at $0.07 per kWh
Payback |
|
$17.78/year
5 months |
Dollar Savings: at $0.10 per kWh
Payback |
|
$25.40/year
3 months |
Dramatic,
short term paybacks in a single-phase run,
with flexibility for future load changes. |
Example
3
Even when larger conduit is required, there may be a quick
payback with wire upsizing. Consider the case of a wye-connected,
three-phase 40 amp lighting load operating only 4000 hours per
year. To simplify, assume the load is concentrated 200 ft.
from the load center. In this example, a total of 5 conductors
are used in a rigid metal conduit: three phase conductors, a
neutral and a full size ground conductor. |
|
#8 AWG |
#6 AWG |
| Conduit Size |
3/4 in. |
1 in. |
| Estimated Loss (at 100% load and 60°C
and 45°C, respective conductor temps.) |
711 W |
426 W |
| Wire Cost |
$117 |
$166 |
| Conduit Cost |
$128 |
$192 |
| Incremental Cost |
|
$113 |
| Energy Savings |
|
1,140 kWh/year |
Dollar Savings: at $0.07 per kWh
Payback |
|
$79.80/year
1 year 5 months |
Dollar Savings: at $0.10 per kWh
Payback |
|
$114.00/year
1 year |
Notice
how much cooler the #6 wire operates.
And less than one and a half year payback at only 4000 hours
operation. |
Special Thanks to the Copper
Development Agency
for allowing us to share this with you.
|
