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SvWhat should I consider when dimensioning cables?
From Basics to Practice
If you already understand the basics of cable sizing, you can proceed to the Cable Sizing Guide or directly to the calculator to calculate the thickness of the cables for your new electrical system.
Otherwise, start dimensioning by answering these three questions:
How long is the cable?
How long is the cable from the power source to the power consumer and back again? This is the question you need to answer. Examples of such circuits are generator → battery → generator, or fuse box → lamp → fuse box.
The shorter the distance, the thinner the cable you can choose.
When you then calculate the cable area, you must remember to count both the plus and minus distance to get the right dimension. For example, there is 2.5 metres between your generator and battery, so you should calculate 5 metres.
How much power?
How much current will flow through the cable? For a lamp or TV, you can find out by looking at how much power it draws and dividing by the voltage, which is normally 12 volts.
So a lamp that draws 24 watts will need 24 / 12 = 2 amps. For a charging circuit, i.e. from generator to battery and back again, the generator’s rated current is used as a reference. A common size of generator is 55 amps.
How much voltage drop?
How much voltage drop can you tolerate in the current circuit? The answer depends on what is connected to the circuit. For the charging circuit, i.e. between the generator and the batteries, our measurements have shown that you should stay below 0.1 volts to maintain good charging.
For a normal consumer like a lantern or a TV, about 0.5 volts voltage drop from the fuse centre is a good level. A bow thruster, anchor winch or starter motor has no problem with a 1 volt voltage drop without losing power, but more than that should be avoided.
