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There seems to be a popular belief that the larger the wire to the device the better it is, but thats not necessarily so. There is a formula that can help you determine what gage you need and how long the wires needs to be before going up in gage. I've seen ads for relay kits that say if you used anything less that 10 gage on the powered device that you can loose up to 1.5 volts which is true if you have a 14 gage wire, 12 volt system, the device pulls 25 amps and the wire is 25 feet long. I've not seen many cooling fans that pull 25 amps and you place them 25 feet from the battery.

In the case of a remote battery it can actualy have a negative effect on the starter if the wire gage is to big. If you need a circuit to shut off when the switch is opened, to large a wire can actually store voltage and continue to power the device until the voltage is depeleted. Now this may be only miliseconds to 1 or 2 second at most but its enough to trash a perfectly good starter drive and flywheel ring gear.

With properly matched devices and circuits you can save a good deal of money and stilll have properly functioning fans or pumps that don't drop voltage. Below is a basic wire selection table for the minimum gage per foot.

 

     WIRE GAUGE SELECTION TABLE

Circuit Amperes

Circuit Watts

Wire gauge (for length in feet)

6V

12V

6V

12V

3'

5'

7'

10'

15'

20'

25'

0 to 2.5

0 to 5

15

30

18

18

18

18

18

18

18

3.0

6

18

36

18

18

18

18

18

18

16

3.5

7

21

42

18

18

18

18

18

18

16

4.0

8

24

48

18

18

18

18

18

16

16

5.0

10

30

60

18

18

18

18

16

16

16

5.5

11

33

66

18

18

18

18

16

16

14

6.0

12

36

72

18

18

18

18

16

16

14

7.5

15

45

90

18

18

18

18

14

14

12

9.0

18

54

108

18

18

16

16

14

14

12

10

20

60

120

18

18

16

16

14

12

10

11

22

66

132

18

18

16

16

12

12

10

12

24

72

144

18

18

16

16

12

12

10

15

30

90

180

18

16

16

14

10

10

10

20

40

120

240

18

16

14

12

10

10

8

25

50

150

300

16

14

12

12

10

10

8

50

100

300

600

12

12

10

10

6

6

4

75

150

450

900

10

10

8

8

4

4

2

100

200

600

1200

10

8

8

6

4

4

There is also a very good calculator at this site with good expliantions of voltage drop. http://www.stealth316.com/2-wire-resistance.htm