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Wire &Wire Management
Table B: Conductors
Sized (AWG) for 3%
Voltage Drop
Use 3% voltage drop for any “critical
application” affecting the safety of the
vessel or its passengers: bilge
pumps, navigation lights, electronics,
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
B or Table C may be calculated by
using the following formula:
CM = K x I x L
E
After calculating the Circular Mil Area
(CM), use Table E 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 the two conductor
sizes).
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 voltage
drop in a decimal expression)
For Example...
Q:
A bilge pump draws 10 amps. The
positive run is 11 feet from the power
panel, including the float switch. The
negative run is only 10 feet. What size
is the wire?
A:
Use the formula to reach the
correct answer:
Table D 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.
3% Voltage Drop at 12 Volts
Current (Amps)
Length 5 10 15 20 25 30 40 50 60 70 80 90 100
10'
3 m 18 14 12 10 10 8 6 6 6 6 6 4 4
15'
5 m 16 12 10 10 8 8 6 6 4 4 4 2 2
20'
6 m 14 10 10 8 6 6 6 4 4 2 2 2 2
25'
8 m 12 10 8 6 6 6 4 4 2 2 2 1 1
30'
9 m 12 10 8 6 4 4 4 2 2 2 2 1 1
40'
12 m 10 8 6 6 4 4 2 2 1 1/0 1/0 2/0 2/0
50'
15 m 10 6 6 4 4 2 2 1 1/0 2/0 3/0 4/0 4/0
60'
18 m 10 6 6 4 2 2 1 1/0 2/0 3/0 3/0 4/0 4/0
70'
21 m 8 6 4 2 2 1 1/0 2/0 3/0 3/0 4/0 4/0
80'
24 m 8 6 4 2 2 1 1/0 2/0 3/0 4/0 4/0
90'
27 m 8 4 2 2 1 1/0 2/0 3/0 4/0 4/0
100' 30 m 6 4 2 2 1 1/0 2/0 3/0 4/0
110' 33 m 6 4 2 2 1 1/0 2/0 3/0 4/0
120' 36 m 6 4 2 1 1/0 2/0 3/0 4/0
130' 40 m 6 2 2 1 1/0 2/0 3/0 4/0
140' 43 m 6 2 2 1/0 2/0 3/0 4/0
150' 46 m 6 2 1 1/0 2/0 3/0 4/0
160' 49 m 6 2 1 1/0 2/0 3/0 4/0
170' 52 m 6 2 1 2/0 3/0 3/0 4/0
3% Voltage Drop at 24 Volts
Current (Amps)
Length 5 10 15 20 25 30 40 50 60 70 80 90 100
10'
3 m 18 18 16 14 12 12 10 10 10 8 8 8 6
15'
5 m 18 16 14 12 12 10 10 8 8 6 6 6 6
20'
6 m 18 14 12 10 10 10 8 6 6 6 6 4 4
25'
8 m 16 12 12 10 10 8 6 6 6 4 4 4 4
30'
9 m 16 12 10 10 8 8 6 6 4 4 4 2 2
40'
12 m 14 10 10 8 6 6 6 4 4 2 2 2 2
50'
15 m 12 10 8 6 6 6 4 4 2 2 2 1 1
60'
18 m 12 10 8 6 6 4 4 2 2 1 1 1/0 1/0
70'
21 m 12 8 6 6 4 4 2 2 1 1 1/0 1/0 2/0
80'
24 m 10 8 6 6 4 4 2 2 1 1/0 1/0 2/0 2/0
90'
27 m 10 8 6 4 4 2 2 1 1/0 1/0 2/0 2/0 3/0
100' 30 m 10 6 6 4 4 2 2 1 1/0 2/0 2/0 3/0 3/0
110' 33 m 10 6 6 4 2 2 1 1/0 1/0 2/0 3/0 3/0 4/0
120' 36 m 10 6 4 4 2 2 1 1/0 2/0 3/0 3/0 4/0 4/0
130' 40 m 8 6 4 2 2 2 1 1/0 2/0 3/0 3/0 4/0 4/0
140' 43 m 8 6 4 2 2 1 1/0 2/0 3/0 3/0 4/0 4/0
150' 46 m 8 6 4 2 2 1 1/0 2/0 3/0 3/0 4/0 4/0
160' 49 m 8 6 4 2 2 1 1/0 2/0 3/0 4/0 4/0 4/0
170' 52 m 8 6 2 2 1 1 2/0 3/0 3/0 4/0 4/0
3% Voltage Drop at 32 Volts
Current (Amps)
Length 5 10 15 20 25 30 40 50 60 70 80 90 100
10'
3 m 18 18 16 16 14 14 12 12 10 10 10 8 8
15'
5 m 18 16 14 14 12 12 10 10 8 8 8 6 6
20'
6 m 18 16 12 12 12 10 10 8 8 6 6 6 6
25'
8 m 18 14 12 12 10 10 8 8 6 6 6 6 4
30'
9 m 16 14 10 10 10 8 8 6 6 6 4 4 4
40'
12 m 16 12 10 10 8 8 6 6 4 4 4 2 2
50'
15 m 14 12 8 8 8 6 6 4 4 2 2 2 2
60'
18 m 14 10 8 8 6 6 4 4 2 2 2 2 1
70'
21 m 12 10 6 6 6 6 4 2 2 2 1 1 0
80'
24 m 12 10 6 6 6 4 4 2 2 1 1 0 0
90'
27 m 12 8 6 6 6 4 2 2 2 1 1/0 1/0 2/0
100' 30 m 12 8 6 6 4 4 2 2 1 1/0 1/0 2/0 2/0
110' 33 m 10 8 6 6 4 4 2 2 1 1/0 1/0 2/0 2/0
120' 36 m 10 8 6 4 4 2 2 1 1/0 1/0 2/0 2/0 3/0
130' 40 m 10 8 6 4 4 2 2 1 1/0 2/0 2/0 3/0 3/0
140' 43 m 10 6 6 4 2 2 1 1/0 1/0 2/0 3/0 3/0 3/0
150' 46 m 10 6 6 4 2 1 1 1/0 2/0 2/0 3/0 3/0 4/0
160' 49 m 10 6 4 4 2 1 1 1/0 2/0 3/0 3/0 4/0 4/0
170' 52 m 8 6 4 2 2 1 1 1/0 2/0 3/0 3/0 4/0 4/0
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