What size wire

Wire and Cable Technical Help - Wire Sizing

Below you'll find a few helpers along the way to properly sizing your wire or cable. As we are primarilly marine focused we have added some tables regarding the amperages as suggested by the ABYC for the marine environment. These standards might be a bit more strict then those in the automotive environment however, they err on the side of caution and were developed with safety in mind.

The volatge drop calculator will allow you to find the percentage of voltage drop as well as the current delivered at the end of the wire run. In the boating world it is suggested:
3% max voltage drop for conductors providing power to panels and switchboards, navigation lighting, bilge blowers, main DC feeders, and any other circuit where voltage drop should be kept to a minimum
10% max voltage drop on conductors used for general lighting and other non-critical circuits

The ampacity (amperage) tables on the left side help to choose the correct size cable to handle the power load for which you are trying to find the correct wiring. There are individual tables for single conductor and multiple conductor runs as current carrying conductors which are bundled together will transfer heat to each other in effect reducing their safe current handling capabilities

Voltage Drop Calculator
designed by Gerald Newton

  

Allowable Amperage of Current Carrying Conductors
Under 50V as suggested by the ABYC

Select Copper or Aluminum

Select American Wire Gauge (AWG) Size

Select Voltage

Enter 1-way circuit
length in feet

Enter Load
in amps


Voltage drop

Voltage at load end of circuit

Per Cent voltage drop

Wire cross section in circular mils

Allowable amperage of single conductors rated 105C
 Size 
 Sq  
    AWG    
SAE
  Ampacity Outside / Inside of Engine Space  
  AWG  
  mm  
 CM area  
CM area 
Outside
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
21
42,000
37,360
160
136
2
34
66,500
62,450
210
178
1
42
83,690
77,790
245
208
1/0
53
105,600
98,980
285
242
2/0
68
133,100
125,100
330
280
4/0
107
211,600
205,500
445
378

Allowable amperage of conductors when multiple conductors
are bundled together for cables rated 105C

Size
2 conductors
3 conductors
4-6 conductors
7-24 conductors
AWG
Sq.mm
Outside Engine Space
Inside Engine Space
Outside Engine Space
Inside Engine Space
Outside Engine Space
Inside Engine Space
Outside Engine Space
Inside Engine Space
18
0.8
20
17.0
14.0
11.9
12.0
10.2
10.0
8.5
16
1
25
21.3
17.5
14.9
15.0
12.8
12.5
10.6
14
2
35
29.8
24.5
20.8
21.0
17.9
17.5
14.9
12
3
45
38.3
31.5
26.8
27.0
23.0
22.5
19.1
10
5
60
51.0
42.0
35.7
36.0
30.6
30.0
25.5
8
8
80
68.0
56.0
47.6
48.0
40.8
40.0
34.0
6
13
120
102.0
84.0
71.4
72.0
61.2
60.0
51.0
4
21
160
136.0
112.0
95.2
96.0
81.6
80.0
68.0
2
34
210
178.5
147.0
125.0
126.0
107.1
105.0
89.3
1
42
245
208.3
171.5
145.8
147.0
125
122.5
104.1
1/0
53
285
242.3
199.5
169.6
171.0
145.4
142.5
121.1
2/0
68
330
280.5
231.0
196.4
198.0
168.3
165.0
140.3
4/0
107
445
378.3
311.5
264.8
267.0
227.0
222.5
189.1

The information provided above is to assist you in properly sizing electical cables for your installation. Best installation methods and practices are also very important to a safe and reliable wiring project. Please do not attempt to work with electricity without a basic knowledge of the dangers involved and please use good judgement. Seek the help of a professional electrician with specific installation questions or when in doubt. Feel free to contact us with any technical questions and we'll do our best to provide the answer or at least guide you in the right direction as to where you can get the help you need.