can be described as the rate at which water flows through a pipe
Watts - power
Ummm... here's where the analogy breaks down a bit....
but work with me here folks. It can best be described as the total volume of water that comes out of the pipe.
watts = volts x amps, so that
6 watts = 12 volts x 0.5 amps, or
6 watts = 6 volts x 1 amp
In case you, like myself, were napping during Algebra 101 that means: amps =watts/volts
volts=watts/amps
Some equipment is rated directly in current draw. Auxiliary fans, fuel pumps and things like that are rated in current draw - Amps. Some equipment is rated in Watts - mostly the lighting equipment. The power requirement in Watts will be printed right on the bulb or stamped in the base.
To come up with amps use one of the formulas shown here. Advanced Concept
Current in Amps = Power in Watts/Voltage in Volts
Current in Amps = Voltage in Volts/Resistance in Ohms
Current in Amps = The Square Root of Power in Watts/Resistance in Ohms
Point 2: Wiring
Use the smallest reasonable sized wire for the required current.
Wire is expensive and the larger you go, the more expensive it is.
Wire is heavy and the larger you go, the heavier it gets.
Mechanically, smaller wire is easier to route, easier to protect, easier to fit connectors on and therefore, more reliable mechanically (There are limits - read on).
Use a large enough wire so there is no
voltage drop.[FIY: All wire has a certain amount of resistance to the flow of current. This resistance causes a drop in the voltage from the source to the load.]
We want whatever it is we are wiring to operate at top efficiency, otherwise it's like throwing away power.
Maintain an adequate safety margin. We don’t want to melt any wires do we? A good rule of thumb is to use one size larger than what is indicated (IMPORTANT: One size larger is actually a SMALLER number ex. 8 guage wire is larger than 12 guage wire)
1. On the left side of the chart, locate the current you will be dealing with.
2. Move across the chart to locate the length of wire needed.
3. Move up to the top of the chart to locate the size of wire to be used.
4. There are several different types of wire available depending on how and where it will be used(i.e., wire designed for resistance to sunlight exposure, high temperatures and direct burial.) It's best to specify wiring that will withstand the worst conditions.
5.For a 24V system multiply the distance taken from the 12V chart by 2.
6.The dashes represent currents which cannot be handled by the wire size.
7.Do not exceed the 2% drop for wire between PV modules and batteries. A 4% to 5% loss is acceptable between batteries and lighting circuits in most cases.
Wire Sizing Chart 12 Volt System
Maximum one-way distance ( feet ) for 2% voltage loss
in 12 volt systems. Wire Size (AWG)
Amps
14
12
10
8
6
4
2
1/0
2/0
4/0
1
45
70
115
180
290
456
720
.
.
.
2
22.5
35
57.5
90
145
228
360
580
720
1060
4
10
17.5
27.5
45
72.5
114
180
290
360
580
6
7.5
12
17.5
30
47.5
75
120
193
243
380
8
5.5
8.5
11.5
22.5
35.5
57
90
145
180
290
10
4.5
7
11.5
18
28.5
45.5
72.5
115
145
230
15
3
4.5
7
12
19
30
48
76.5
96
150
20
2
3.5
5.5
9
14.5
22.5
36
57.5
72.5
116
25
1.8
2.8
4.5
7
11.5
18
29
46
58
92
30
1.5
2.4
3.5
6
9.5
15
24
38.5
48.5
77
40
-
-
2.8
4.5
7
11.5
18
29
36
56
50
-
-
2.3
3.6
5.5
9
14.5
23
29
46
100
-
-
-
-
2.9
4.6
7.2
11.5
14.5
23
150
-
-
-
-
-
-
4.8
7.7
9.7
15
200
-
-
-
-
-
-
3.6
5.8
7.3
11
NEC allows rounding up cable ampacity to next standard fuse
or breaker.
Point 3: Ohm's Law (as regards resistance) Advanced Concept
Ohm's law is one of the most important concepts in electronics. Fortunately it's only a very simple mathematical relationship between current, voltage, and resistance.
According to the Ohm's law, voltage equals current times resistance which is expressed in the following equation:
E=IR
where E = voltage, I = current, and R = resistance
For example, if
I = 0.1A
R = 10k
then
E = 0.1 * 10k
E = 1000 volts
Note: "k" stands for "thousands". So 10k = 10,000 ohm
Every effort is taken in order to maintain accuracy in the information contained within this web site. Although all of the information is believed to be accurate you are encouraged to consult other sources for additional information or clarification. Under no circumstances shall the authors of this site be held liable for the use of the information or of its consequences. Electrical code varies from county to county, and within the US, it varies, to some extent from state to state.
We take no responsibility for the content of outside links. Outside links may NOT reflect our philosophy or beliefs.
![[line]](/fs_img/builder/builder46/line.gif){kind=small}