I have had few e mails from readers asking for extra information on boat wiring. Whole books have been written on the subject and I am certain that wiring on a boat is something I will be returning to again and again in On Board.
To help you get started here is table to assist you in choosing the correct size cable for almost any job on board.
The chart is fairly easy to follow but a few tips may help if you are at all unfamiliar with electrical wiring. The column on the left is the distance in feet that the cable will run and the maximum amperage draw on the circuit is shown across the top starting at 5 amps and finishing at 100.
As an example say you want to install a 25 watt light located 30 feet from the distribution panel then the first thing to do is figure out the amps that the light will draw.
AMPS = Watts/Volts thus 25 watts /12 volts = 2.08 amps. As the smallest cable listed is for 5 amps we will use this and in any event you should always round up to the next larger size if the number falls between two of the amperage figures. Following the 5 amp column down we see that the size next to 30 feet is 12 AWG (American Wire gauge) but, when calculating the figures it is the complete circuit length that we are concerned with which is double the 30 feet as the cable has to run to the light fitting and back to the panel making this 60 feet in total which makes this 10 AWG, the next size larger.
Using the wrong size cable will lead to voltage drop and in this case would cause the light to be dim and in cases where the cable is way undersized could lead to overheating of the circuits.
Regular readers will know that I am a keen advocate for LED lighting which draw significantly less current than incandescent bulbs. Given the price of copper cable considerable cost and weight savings can be made as the cables needed to supply LED will be significantly lighter in gauge.
One final point, using the correct colored cable helps in tracing circuits later. The universally accepted colors are listed below. The chart may look a little small on your computer screen but you can make it larger by clicking anywhere on it which will make it easier to read.
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