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Wiring Boats
Table A: Marine Wire Color Code
| Color |
Item |
Use |
| Yellow or Blk |
Ground |
Return, Negative Mains |
| Lt. Blue |
Oil Pressure |
Oil Pressure Sender to Gauge |
| Dk. Blue |
Cabin & Instrument |
Fuse or Switch to Lights |
| Brown |
Generator Armature |
Generator Armature to Regulator |
| |
Alternator Charge Light |
Generator Terminal or Alternator Auxiliary Terminal to Regulator |
| |
Pumps |
Fuse or Switch to Pumps |
| Green |
Bonding System |
Bonding Wires (if insulated) |
| Grey |
Navigation Lights |
Fuse or Switch to Lights |
| |
Tachometer |
Tachometer Sender to Gauge |
| Orange |
Accessory Feed |
Ammeter to Alternator or Generator Output and Accessory Fuses or Switches |
| |
Common Feed |
Distribution Panel to Accessory Switch |
| Pink |
Fuel Gauge |
Fuel Gauge Sender to Gauge |
| Purple |
Ignition |
Ignition Switch to Coil & Electrical Instrument |
| |
Instrument Feed |
Distribution Panel Electrical Instruments |
| Red |
Main Power Feeds |
Positive Mains (particularly unfused) |
| Yellow |
Generator Field |
Generator to Regulator Field Terminal |
| Brn w/Yellow |
Bilge Blowers |
Fuse or Switch to Blower |
| Yellow w/Red |
Starting Circuit |
Starting Switch to Solenoid |
Table B: Conductor Sizes
Ampacity is the ultimate safe current carrying capacity of the wire before damage occurs to the insulation, without regard to voltage drop. Because the insulation of most SAE wire types is not the same as AWG, this chart should not be used for other conductor types. Use Table C & D to find proper wire size to insure adequate performance.
| AWG |
Sq.
mm |
AWG
CM area |
SAE
CM Area |
Ampacity
Engine Space
Outside |
Ampacity
Engine Space
Inside |
| 18 |
0.8 |
1,600 |
1,537 |
20 |
17 |
| 16 |
1 |
2,600 |
2,336 |
25 |
21 |
| 14 |
2 |
4,100 |
3,702 |
35 |
30 |
| 12 |
3 |
6,500 |
5,833 |
45 |
38 |
| 10 |
5 |
10,500 |
9,343 |
60 |
51 |
| 8 |
8 |
16,800 |
14,810 |
80 |
68 |
| 6 |
13 |
26,600 |
24,538 |
120 |
102 |
| 4 |
19 |
42,000 |
37,360 |
160 |
130 |
| 2 |
32 |
66,500 |
62,450 |
210 |
178 |
| 1 |
40 |
83,690 |
77,790 |
245 |
208 |
| 1/0 |
50 |
105,600 |
98,980 |
285 |
242 |
| 2/0 |
62 |
133,100 |
125,100 |
330 |
280 |
| 3/0 |
81 |
167,800 |
158,600 |
385 |
327 |
| 4/0 |
103 |
211,600 |
205,500 |
445 |
378 |
Table C: Conductor Sizes (AWG) for 3% Voltage Drop at 12 Volts
| Length |
5 |
10 |
15 |
20 |
25 |
30 |
40 |
50 |
60 |
70 |
80 |
90 |
100 |
| 10' |
18 |
14 |
12 |
12 |
10 |
10 |
8 |
8 |
6 |
6 |
6 |
4 |
4 |
| 15' |
16 |
12 |
10 |
10 |
8 |
8 |
6 |
6 |
4 |
4 |
4 |
2 |
2 |
| 20' |
14 |
12 |
10 |
8 |
8 |
6 |
6 |
4 |
4 |
4 |
2 |
2 |
2 |
| 25' |
14 |
10 |
8 |
8 |
6 |
6 |
4 |
4 |
2 |
2 |
2 |
1 |
1 |
| 30' |
12 |
10 |
8 |
6 |
6 |
4 |
4 |
2 |
2 |
2 |
1 |
1/0 |
1/0 |
| 40' |
12 |
8 |
6 |
6 |
4 |
4 |
2 |
2 |
1 |
1/0 |
1/0 |
2/0 |
2/0 |
| 50' |
10 |
8 |
6 |
4 |
4 |
2 |
2 |
1 |
1/0 |
1/0 |
2/0 |
3/0 |
3/0 |
| 60' |
10 |
6 |
6 |
4 |
2 |
2 |
1 |
1/0 |
2/0 |
2/0 |
3/0 |
3/0 |
4/0 |
| 70' |
10 |
6 |
4 |
2 |
2 |
2 |
1/0 |
2/0 |
2/0 |
3/0 |
3/0 |
4/0 |
4/0 |
| 80' |
8 |
6 |
4 |
2 |
2 |
1 |
1/0 |
2/0 |
3/0 |
3/0 |
4/0 |
|
|
| 90' |
8 |
4 |
4 |
2 |
1 |
1/0 |
2/0 |
3/0 |
3/0 |
4/0 |
|
|
|
| 100' |
8 |
4 |
2 |
2 |
1 |
1/0 |
2/0 |
3/0 |
4/0 |
4/0 |
|
|
|
| 110' |
8 |
4 |
2 |
2 |
1 |
1/0 |
2/0 |
3/0 |
4/0 |
|
|
|
|
| 120' |
6 |
4 |
2 |
1 |
1/0 |
2/0 |
3/0 |
4/0 |
4/0 |
|
|
|
|
| 130' |
6 |
4 |
2 |
1 |
1/0 |
2/0 |
3/0 |
4/0 |
|
|
|
|
|
| 140' |
6 |
2 |
2 |
1/0 |
2/0 |
2/0 |
3/0 |
4/0 |
|
|
|
|
|
| 150' |
6 |
2 |
1 |
1/0 |
2/0 |
3/0 |
4/0 |
|
|
|
|
|
|
| 160' |
6 |
2 |
1 |
1/0 |
2/0 |
3/0 |
4/0 |
|
|
|
|
|
|
| 170' |
6 |
2 |
1 |
2/0 |
3/0 |
3/0 |
4/0 |
|
|
|
|
|
|
Use 3% voltage drop for any "critical application" affecting the safety of the vessel or its passengers: bilge pumps, navigation lights, electronics, etc...
Table D: Conductor Sizes (AWG) for 10% Voltage Drop at 12 Volts
| Length |
5 |
10 |
15 |
20 |
25 |
30 |
40 |
50 |
60 |
70 |
80 |
90 |
100 |
| 10' |
18 |
18 |
18 |
16 |
16 |
14 |
14 |
12 |
10 |
8 |
8 |
6 |
6 |
| 15' |
18 |
18 |
16 |
16 |
14 |
14 |
12 |
12 |
10 |
8 |
8 |
6 |
6 |
| 20' |
18 |
16 |
16 |
14 |
12 |
12 |
10 |
10 |
8 |
8 |
8 |
6 |
6 |
| 25' |
18 |
16 |
14 |
12 |
12 |
10 |
10 |
8 |
8 |
8 |
6 |
6 |
6 |
| 30' |
18 |
16 |
14 |
12 |
10 |
10 |
8 |
8 |
8 |
6 |
6 |
6 |
4 |
| 40' |
16 |
14 |
12 |
10 |
10 |
8 |
8 |
6 |
6 |
6 |
4 |
4 |
4 |
| 50' |
16 |
12 |
10 |
10 |
8 |
8 |
6 |
6 |
4 |
4 |
4 |
4 |
2 |
| 60' |
16 |
12 |
10 |
8 |
8 |
8 |
6 |
4 |
4 |
4 |
2 |
2 |
2 |
| 70' |
14 |
12 |
10 |
8 |
8 |
6 |
6 |
4 |
4 |
2 |
2 |
2 |
2 |
| 80' |
14 |
10 |
8 |
8 |
6 |
6 |
4 |
4 |
2 |
2 |
2 |
2 |
1 |
| 90' |
14 |
10 |
8 |
8 |
6 |
6 |
4 |
4 |
2 |
2 |
2 |
1 |
1 |
| 100' |
12 |
10 |
8 |
6 |
6 |
4 |
4 |
2 |
2 |
2 |
1 |
1 |
1/0 |
| 110' |
12 |
10 |
8 |
6 |
6 |
4 |
4 |
2 |
2 |
1 |
1 |
1/0 |
1/0 |
| 120' |
12 |
8 |
8 |
6 |
4 |
4 |
2 |
2 |
2 |
1 |
1/0 |
1/0 |
2/0 |
| 130' |
12 |
8 |
6 |
6 |
4 |
4 |
2 |
2 |
1 |
1 |
1/0 |
2/0 |
2/0 |
| 140' |
12 |
8 |
6 |
6 |
4 |
4 |
2 |
2 |
1 |
1/0 |
1/0 |
2/0 |
2/0 |
| 150' |
10 |
8 |
6 |
4 |
4 |
2 |
2 |
1 |
1 |
1/0 |
2/0 |
2/0 |
3/0 |
| 160' |
10 |
8 |
6 |
4 |
4 |
2 |
2 |
1 |
1/0 |
1/0 |
2/0 |
2/0 |
3/0 |
| 170' |
10 |
8 |
6 |
4 |
4 |
2 |
2 |
1 |
1/0 |
2/0 |
2/0 |
3/0 |
3/0 |
Use 10% voltage drop for any "non-critical applications: windlasses, cabin lights, etc...
Important!
Length (feet): Determined by measuring the length of the conductor from the positive (+) power source connection to the electrical device and back to the negative (-) power source connection. Note that the power source connection may be either the battery, panelboard or switchboard.
Current (amps): Determined by adding the total amps on a circuit.
Conductor sizes not covered in Table C or Table D may be calculated by using the following formula:
After calculating the Circular Mil Area (CM), use Table B to determine the proper conductor size (National Fire Protection Agency and Coast Guard require that the next larger conductor be used when the calculated CM area falls between two conductor sizes).
CM=K x l x L / E
CM = Circular Mil area of Conductors
K = 10.75 (Constant representing the mil-foot resistance of copper)
I = Current - amps
L = Length - feet
E = Voltage drop at load (in volts)
For Example...
Q: For example: A bilge pump draws 10 amps. The positive run is l l feet from the power panel, including the float switch. The negative run is only 10 feet. What size wire?
A: Use the formula to reach the correct answer:
CM = 10.75 x 10 (amps) x 21 (total length of run) / 0.36 (3% of 12v) = 6,271
Table "B" shows that 12 AWG wire has a CM area of 6,500 and is the correct choice. However, SAE wire has a CM area of only 5,833. Under NFPA and USCG regulations, 10 SAE wire must be used.
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