At first glance the math involved in calculating copper losses may appear awkward, but don't worry. A common calculator with basic functions makes it easy. A basic understanding of Ohm's Laws for electricity is helpful, but not necessary. An copy of the National Electrical Code, even a copy a few years old, will go a long way in helping you find information on the conductors you wish to calculate losses for.
Things You'll Need
- National Electrical Code book or a NEC pocket reference
- Measured length of a conductor in feet
- Size of conductor in American wire gauge or kcm
- Amount of current in amps that will be applied to the conductors
Open the NEC book to chapter 9, table 8, called conductor properties. Locate the size and type (solid or stranded) of wire and scan across to the ohm/kFt column. This is one of the values you will need. For example, 12 gauge stranded wire has 2.05 ohms of resistance per every 1000 feet.
Insert the value from Step 1 into the following equation. Insert the measured length of the circuit into the equation.
L2/1000 * R = RT = Total DC resistance of circuit conductors
L= length of circuit R = conductor resistance per 1000 Ft (from step one)
examples : L = 250 Ft R = 2.05 (# 12 stranded wire)
With a calculator, solve for above equation from left to right. The following example is based on a 250 foot circuit using #12 AWG.
(250)2/1000 2.05 = RT
500/1000 2.05 = RT
.5 * 2.05 = RT
1.025 ohms = RT
Wire losses are generally given as I²R which is also an Ohm's law for power. The unit used for these losses will therefore be watts or W for short. This is used because losses are basically electrical power given off in the form of heat. Insert the value you got for RT in Step 3 and the expected full load current (given in amps or A) for the circuit into the loss formula below.
I²RT = Loss in watts
10 amps ² * 1.025 ohms = Loss in watts
With a calculator, solve for above equation from left to right. Below an example is given for a ten amp load using a 250 Ft. circuit with #12 gauge wire.
10 amps ² 1.025 ohms = Loss in watts
100 1.025 = Loss in watts
102.5 W = Loss in watts
Tips & Warnings
- Look over the article at least once before starting any math. Use the practice examples to check your math.
- Another way of looking at electrical losses is pressure losses known as "voltage drop."This can be found in NEC article 215.2A Fine Print Note No. 4.
- Due to the differences in local building codes, this article is primarily for academic use. Before using this information for actual application consult your local and federal building codes and laws.
- Photo Credit Zedcor Wholly Owned/PhotoObjects.net/Getty Images
Jaw Wiring and Weight Loss
Many people have taken drastic methods in order to lose weight. By wiring your jaw closed, you are invariably forcing yourself to...
How to Determine the Wire Gauge for DC Voltage
Electricity is harnessed in two forms: direct current (DC), in which electricity flows in one direction only, and alternating current (AC), where...
How to Calculate the Heat Loss in a Pipe
Engineers or designers who need to transport hot fluids through pipe over a distance need to account for the natural heat loss...
How to Calculate dB Loss
Decibels (dB) determine the relationship in signal strength between two sources. When the power of the first signal outweighs that of the...
How to Calculate Head Loss
Head loss is a common term used to describe two types of pressure loss in a liquid system. The first type is...
How to Calculate Transmission Line Losses
As electrical transmission lines span hundreds of miles, there will be some load loss incurred. The longer the line, the more electricity...
How to Calculate Loss in a Coax Cable
Coax cable is used to connect many electronics devices, including televisions, DVD players, cable television boxes, radio antennas and computers. The standard...
Cable Length vs. Power Drop
The power drop, or power lost in a cable, depends on the cable length, cable size and the current through the cable....
Friction Factors for Type K Copper Tubing
Type K copper tubes are thick-walled -- much thicker than type L or type M copper tubing. Because K, L and M...