Technical Information

Cable Conductor Size & Current Ratings

Conductor Requirements for ISO 10133 and ISO 13297

This appendix is reproduced from Annex 'A' (normative) of both ISO 10133 and 13297. Both ISOs are supporting Standards to the Recreational Directive. The use of these recommendations can be used to demonstrate compliance to this Directive.

Current Ratings

The table gives allowable continuous current ratings in amperes determined for an ambient temperature of 30°C and the minimum number of strands for conductors.

Conductor cross-sectional area, allowable continuous current and stranding.
Maximum Current in amps for a single conductor at insulation temperature ratings
Cross sectional Area mm2 60°C 70°C 85 to 90°C 105°C 125°C 200°C Minimum number of strands
Type A* Type B*
0.75
6
10
12
16
20
25
16
1
8
14
18
20
25
35
16
1.5
12
18
21
25
30
40
19
26
2.5
17
25
30
35
40
45
19
41
4
22
35
40
45
50
55
19
65
6
29
45
50
60
70
75
19
105
10
40
65
70
90
100
120
19
168
16
54
90
100
130
150
170
37
266
25
71
120
140
170
185
200
49
420
35
87
160
185
210
225
240
127
665
50
105
210
230
270
300
325
127
1064
70
135
265
285
330
360
375
127
1323
95
165
310
330
390
410
430
259
1666
120
190
360
400
450
480
520
418
2107
150
220
380
430
475
520
560
418
2107

Notes:
Conductor current ratings may be interpolated for cross sectional areas between those shown in the Table.

* Conductors with at least a Type A stranding shall be used for general wiring of craft. Conductors with Type B stranding shall be used for any wiring where frequent flexing is involved during use.

For conductors in engine rooms (60ºc ambient), the maximum current rating in the table shall be de-rated by the factors:-
Temperature rating of conductor insulation °C Multiply maximum current from table above by
70
0.75
85 to 90
0.82
105
0.86
125
0.89
200
1.0
Bundling (For AC only)
When more than three AC conductors are bundled together the maximum current ratings in the table shall be de-rated by the factor below:-
Number of conductors bundled Multiply maximum current from A1 by
4 to 6
0.7
7 to 24
0.6
25 or more
0.5

Notes:
De-rating reductions for temperature and building are cumulative where applicable. Bundling reduction factors are not normally considered necessary for DC cables in small craft.

Volt drop calculations

For information, (extra low voltage DC only) the volt drop on load may be calculated by using the following formula: -

E= 0.0164 x I x L
S

Where

E = Volts drop in volts

S = the conductor cross-section area in square millimetres

I = the load current in amperes

L = the total length, in metres, of conductor from the positive power source Connection to the electrical device and back to the negative source connection.

Metric Cable Size to AWG Conversion Tables

AWG
Metric Equivalent mm sq.
Metric Cable Size mm sq
20
0.52
0.75
18
0.82
1.0
16
1.32
1.5
14
2.1
2.5
12
3.3
4
10
5.32
6
8
8.5
10
6
13.5
15
4
21.3
25
2
33.7
35
1/0 (0)
53
70.0
(50.0 if current capacity not exceeded)
2/0 (00)
67.6
70
3/0 (000)
84.4
95
4/0 (0000)
107
120

State of Charge

The following table will allow conversion of the readings obtained to an estimate of state of charge. The table is good for the batteries at 25 deg. C (77 deg F) that have been at rest for 3 hours or more. If the batteries are at a lower temperature you can expect lower voltage readings

Percent of full charge 12 Volt DC system 24 Volt DC system
100%
12.7
25.4
90%
12.6
25.2
80%
12.5
25
70%
12.3
24.6
60%
12.2
24.4
50%
12.1
24.2
40%
12.0
24
30%
11.8
23.6
20%
11.7
23.4
10%
11.6
23.2
0%
11.6
23.2