How To Determine Wire Sizes In Ac Vs Dc Circuits

Wire Sizing Chart and Formula

This nautical chart is useful for finding the correct wire size for whatsoever voltage, length, or amperage menstruum in any Ac or DC excursion. For most DC circuits, especially between the PV modules and the batteries, we try to go on the voltage drop to three% or less. There'southward no sense using your expensive PV wattage to estrus wires. You lot desire that power in your batteries!

Note: This formula doesn't directly yield a wire gauge size, but rather a "VDI" number, which is and then compared to the nearest number in the VDI column, and and so read across to the wire gauge size column.

1. Calculate the Voltage Drop Alphabetize (VDI) using the following formula:

VDI = AMPS x Feet ÷ (% VOLT DROP 10 VOLTAGE)

Amps = Watts divided past volts
Feet = One-way wire distance
% Volt Driblet = Percentage of voltage drib acceptable for this circuit (typically 2% to v%)

2. Decide the appropriate wire size from the chart below.

Take the VDI number you only calculated and find the nearest number in the VDI column, then read to the left for AWG wire gauge size.
Be certain that your excursion amperage does non exceed the effigy in the Ampacity column for that wire size. (This is non usually a problem in low-voltage circuits).

Example: Your PV array consisting of four 75W modules is 60 anxiety from your 12-volt battery. This is actual wiring distance, up pole mounts, around obstacles, etc. These modules are rated at 4.4 amps x 4 modules = 17.6 amps maximum. Nosotros'll shoot for a 3% voltage driblet. Then our formula looks like:

VDI =

17.six x 60
iii[%] x 12[5]

= 29.3

Looking at our chart, a VDI of 29 means we'd amend use #2 wire in copper, or #0 wire in aluminum. Hmmm. Pretty large wire. What if this arrangement was 24-volt? The modules would be wired in series and so each pair of modules would produce 4.four amps. Ii pairs x 4.4 amps = 8.eight amps max.

Wire Size	Copper Wire		Aluminum Wire
AWG	VDI	Ampacity	VDI	Ampacity
0000	99	260	62	205
000	78	225	49	175
00	62	195	39	150
0	49	170	31	135
two	31	130	20	100
4	20	95	12	75
6	12	75	•	•
8	viii	55	•	•
10	five	30	•	•
12	3	20	•	•
14	2	15	•	•
sixteen	1	•	•	•

Chart developed by John Davey and Windy Dankoff. Used with permission.

Source: "PHOTOVOLTAICS - Blueprint and Installation Manual" past Solar Energy International.

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