Electrical Reference

Bike-specific information can be found in ST13.ElectricalReference.

Useful Articles

The Boat Owners Association of the US (BoatUS, http://www.boatus.com) has an excellent set of how-to guides on various boat-related subjects including a number on electrical systems. Just about everything in those articles is relevant to motorcycles.

WARNING: The ampacity figures in these articles are for marine-grade cable, which has insulation rated for 105°C. Conventional cable is rated for much less and will carry much less current before the insulation fails. Marine-grade cable is an excellent choice for use on motorcycles because it does a better job resisting water, salt, oil, fuel and other substances you might find on your bike.

• Electrical Systems: http://www.boatus.com/boattech/electric.htm
• 12 Volt Systems: http://www.boatus.com/boattech/12volt.htm
• Circuit Protection for DC Systems: http://www.boatus.com/boattech/CircuitProtect.htm
• Electrical Connections: http://www.boatus.com/boattech/casey/05.htm
• Wiring: http://www.boatus.com/boattech/wiring.htm
• Electrical Theory: http://www.ibiblio.org/kuphaldt/electricCircuits

Wire and Fuse Selection

Wire of a certain size is only capable of carrying a certain amount of current (measured in Amps). This spreadsheet (MS Excel, 12K) will allow you to calculate the minimum wire size required for a circuit of a given length carrying a given amount of current.

WARNING: The warning about about marine-grade cable also applies here.

Blue Sea Systems has a useful chart with similar information: http://assets.bluesea.com/files/resources/reference/20010.pdf

Watts to Amperes at 12 Volts

The formula for this is Amperes = Watts / Volts. To go the other way, Watts = Amperes * Volts.

Watts	Amps		Watts	Amps		Watts	Amps		Watts	Amps		Watts	Amps		Watts	Amps
1	0.08		51	4.25		101	8.42		151	12.58		201	16.75		251	20.92
2	0.17		52	4.33		102	8.50		152	12.67		202	16.83		252	21.00
3	0.25		53	4.42		103	8.58		153	12.75		203	16.92		253	21.08
4	0.33		54	4.50		104	8.67		154	12.83		204	17.00		254	21.17
5	0.42		55	4.58		105	8.75		155	12.92		205	17.08		255	21.25
6	0.50		56	4.67		106	8.83		156	13.00		206	17.17		256	21.33
7	0.58		57	4.75		107	8.92		157	13.08		207	17.25		257	21.42
8	0.67		58	4.83		108	9.00		158	13.17		208	17.33		258	21.50
9	0.75		59	4.92		109	9.08		159	13.25		209	17.42		259	21.58
10	0.83		60	5.00		110	9.17		160	13.33		210	17.50		260	21.67
11	0.92		61	5.08		111	9.25		161	13.42		211	17.58		261	21.75
12	1.00		62	5.17		112	9.33		162	13.50		212	17.67		262	21.83
13	1.08		63	5.25		113	9.42		163	13.58		213	17.75		263	21.92
14	1.17		64	5.33		114	9.50		164	13.67		214	17.83		264	22.00
15	1.25		65	5.42		115	9.58		165	13.75		215	17.92		265	22.08
16	1.33		66	5.50		116	9.67		166	13.83		216	18.00		266	22.17
17	1.42		67	5.58		117	9.75		167	13.92		217	18.08		267	22.25
18	1.50		68	5.67		118	9.83		168	14.00		218	18.17		268	22.33
19	1.58		69	5.75		119	9.92		169	14.08		219	18.25		269	22.42
20	1.67		70	5.83		120	10.00		170	14.17		220	18.33		270	22.50
21	1.75		71	5.92		121	10.08		171	14.25		221	18.42		271	22.58
22	1.83		72	6.00		122	10.17		172	14.33		222	18.50		272	22.67
23	1.92		73	6.08		123	10.25		173	14.42		223	18.58		273	22.75
24	2.00		74	6.17		124	10.33		174	14.50		224	18.67		274	22.83
25	2.08		75	6.25		125	10.42		175	14.58		225	18.75		275	22.92
26	2.17		76	6.33		126	10.50		176	14.67		226	18.83		276	23.00
27	2.25		77	6.42		127	10.58		177	14.75		227	18.92		277	23.08
28	2.33		78	6.50		128	10.67		178	14.83		228	19.00		278	23.17
29	2.42		79	6.58		129	10.75		179	14.92		229	19.08		279	23.25
30	2.50		80	6.67		130	10.83		180	15.00		230	19.17		280	23.33
31	2.58		81	6.75		131	10.92		181	15.08		231	19.25		281	23.42
32	2.67		82	6.83		132	11.00		182	15.17		232	19.33		282	23.50
33	2.75		83	6.92		133	11.08		183	15.25		233	19.42		283	23.58
34	2.83		84	7.00		134	11.17		184	15.33		234	19.50		284	23.67
35	2.92		85	7.08		135	11.25		185	15.42		235	19.58		285	23.75
36	3.00		86	7.17		136	11.33		186	15.50		236	19.67		286	23.83
37	3.08		87	7.25		137	11.42		187	15.58		237	19.75		287	23.92
38	3.17		88	7.33		138	11.50		188	15.67		238	19.83		288	24.00
39	3.25		89	7.42		139	11.58		189	15.75		239	19.92		289	24.08
40	3.33		90	7.50		140	11.67		190	15.83		240	20.00		290	24.17
41	3.42		91	7.58		141	11.75		191	15.92		241	20.08		291	24.25
42	3.50		92	7.67		142	11.83		192	16.00		242	20.17		292	24.33
43	3.58		93	7.75		143	11.92		193	16.08		243	20.25		293	24.42
44	3.67		94	7.83		144	12.00		194	16.17		244	20.33		294	24.50
45	3.75		95	7.92		145	12.08		195	16.25		245	20.42		295	24.58
46	3.83		96	8.00		146	12.17		196	16.33		246	20.50		296	24.67
47	3.92		97	8.08		147	12.25		197	16.42		247	20.58		297	24.75
48	4.00		98	8.17		148	12.33		198	16.50		248	20.67		298	24.83
49	4.08		99	8.25		149	12.42		199	16.58		249	20.75		299	24.92
50	4.17		100	8.33		150	12.50		200	16.67		250	20.83		300	25.00

-- MarkFeit - 24 Sep 2005