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Old 02-17-2008, 09:21 AM   #1
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tkendall's Avatar
1976 31' Sovereign
Anytown USA , The open road.
Join Date: Jan 2008
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Wire Size Help

The question has been asked and debated in some other thread. Here is a simple way to figure your wire size needed in your remodel or repair project.

This will work finding the correct wire size for any voltage, length, or amperage flow in any AC or DC circuit.

The idea is to keep your wires from getting hot. Hot wires can lead to melted wires or a fire.

This formula does not give you your wire size, but the VDI number (Voltage Drop Index)

Calculate VDI:


Amp = watts divided by volts

Feet = one way wire length

% of voltage drop = Percent of drop acceptable for the circuit (2-5%)

Determine the apporiate wire size from the chart below.

Take the VDI number you calculated and find in the chart. The follow that line to the AWG wire size.

Make sure your circuit amperage does not exceed the figure in the Ampacity column for the wire size. (not a big problem with low-voltage circuits.)

(will post chart when I can get it to show up here)

Now, take in consideration that your amp draw at any one time isn't going to be that high. If you use the total amp output of a 45 amp converter your going to have monster wire. You need to know what your appliance uses in amps. For example, you are figuring your fridge. Mine uses 1.5 amps at 12 volts for controls and such, running on propane. Your largest use on the DC side will be you converter/charger, charging your battery when plugged into shore power. Your cables will be larger going to your battery than any other wire.

Always fuse everything! Never use a higher fuse rating than recommended!

Sample amp draw DC appliances: (these are aprox. always check to be sure)

3-way fridge: 1.5-5 amps
Furnace motor: 7 amps
Water Pump: 4-7 amps
Lights: usually marked in watts. watts x volts = amps
Radio: 1-3 amps

Good wiring!

Genuis has limitations, stupidity has none.
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Old 04-13-2008, 10:58 AM   #2
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1966 24' Tradewind
Valley Village , California
Join Date: Feb 2008
Posts: 23
Originally Posted by tkendall
(will post chart when I can get it to show up here)
I would love to see that chart... when you get a minute...

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Old 04-13-2008, 11:44 AM   #3
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1999 34' Excella
Joshua , Texas
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You can also do a Google search for "wire size calculator" and find several on-line.
History doesn't repeat itself, people do!
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