Question about 12 volt wire size tables

[BoatBumm]

This probably falls under the stupid questions category. But the commonly available tables for what wire size to use for a given 12 volt load in amps and distance are to me ambiguous about what they mean by "distance". If the load is 20 feet from the battery, do I use the 20 feet as the distance, or is it really 40 feet since the two wires (power & ground) each have to go 20 feet, for a total of 40 feet? Thanks!

[Chotu]

It’s 20 feet. They are referencing the distance of each individual wire to the load.

[Bycrick]

You actually have to read the instructions for the table or app. Some use distance one way, others use distance both ways.

[BoatBumm]

The versions of the table I’ve seen don’t mention if it’s for one wire one way or both wires, or else I wouldn’t be asking. But thanks for responding.

[markcouz]

Originally Posted by Chotu

It’s 20 feet. They are referencing the distance of each individual wire to the load.

Interesting, the tables and calculators that I have used all refer to total wire length - maybe we use different sources so not such a dumb question after all.

[FlyingScot]

Skip the tables and confusion. Use an app like DC Wire Sizer and you can put in way more details and get much more precise information.

This is not an area to skimp.

[markcouz]

On the other hand I think Chotu made a typo with the 20ft - if they are referencing each individual wire (as per his comment) then it is 40ft, 20 positive and 20 negative - then we agree.

[Bycrick]

I have three apps for wire sizing. One uses distance on way, one uses distance both ways, and the third didn’t say, so I quit using it, even though I could have figured it out. Both methods work. The "both ways" system works as long as both wires are equal length. If they’re not, then the single direction system is easier. Any app or table that doesn’t clearly tell you how it works should be avoided.

[HeywoodJ]

Both Blue Seas and Engineering Toolbox are explicit that their tables are based on total wire length, there and back. If you're table doesn't say then you need to find a new table.

If for some reason you are really enamored of the table, then find a table or calculator that does specify, run a few sample calculations, and compare those with your favorite table to determine if it is one-way or roundtrip distance.

[BoatBumm]

I didn’t know about that app. DC Wire Sizer. That’s perfect! Thanks. (One of my favorite phrases is: “You don’t know what you don’t know.” - very true here)

[mvweebles]

Link to Blue Sea table. Note the terminology "circuit length." It's not ambiguous nor vague but you have to dissect the meaning of Circuit Length. In some applications, a ground is very close but the hot is a distance away. For example, in automotive applications, you can often grab a nearby ground off the frame but run power from a fuse block some distance away. The circuit length would be the sum of course.

https://www.bluesea.com/resources/1437

http://assets.bluesea.com/files/reso...on_chartlg.jpg

[Montanan]

Wire Sizing Chart | Fetting Power, Inc.

[boatpoker]

ABYC E-11 Clearly states distance includes both - and +

i.e. "Length of conductor from source of Current to Device and back to
Source in Feet" as shown on their tables.

[FlyingScot]

Originally Posted by mvweebles

Link to Blue Sea table. Note the terminology "circuit length." It's not ambiguous nor vague but you have to dissect the meaning of Circuit Length. In some applications, a ground is very close but the hot is a distance away. For example, in automotive applications, you can often grab a nearby ground off the frame but run power from a fuse block some distance away. The circuit length would be the sum of course.

https://www.bluesea.com/resources/1437

http://assets.bluesea.com/files/reso...on_chartlg.jpg

Terminology is important. Since they OP is talking about 12V DC wiring there is no "hot" or "ground" when it comes to circuit length for wire size/voltage drop calculation.

Positive and Negative are the proper terms.

[Senojev]

What boat poker says👍