Wire Size

[kittysmitty]

Simple question. I have #10 wire available.If I were to double up on the runs, ie 2 lengths for Pos, and two lengths for Neg, what is the size now. From what I can find I think it's now #4. Am I correct? Thanks

[SteveCH]

According to a friend who is a physicist and whom I asked about this some time ago, yes.

[ghurd]

It is more like #7.

Compare the circular mill area.

Rule of thumb- double the wires, subtract 3.  (10-3=7)

G-

[kittysmitty]

Yes, subtract 3, that was one of my calculations. #10 minus 3 is #4. Correct me if I am wrong, but I don't think odd numbers exist.

[Tritium]

Well I know #13, #15 and #17 exist in magnet wire. I think those are odd sizes. The formula subtract 3 means that 2 wires of #10 = 1 wire of #7.

Thurmond

[ghurd]

Odd doesn't matter.  I use #1 sometimes.

Not sure how you get 10 minus 3 is 4.

It looks like you are thinking about the wire diameter.

Two pieces of #10 would fit side by side, in the same hole as a piece of #4.

The empty space is not carrying current, so that area cannot be included.

"Compare the circular mill area."

The circular mils is the part that carries the current.  That's what is important.

The circular mils of #10 is about 10,000.

Two pieces of #10 will have about 20,000 circular mills, and that's about #7.

Four pieces of #10...

Two #10 is #10-3=#7, and two #7 is #7-3=#4.  

It holds up as a quick rule of thumb.  #4 is about 40,000 circular mills, same as 4 x the 10,000 of #10.

G-

[richhagen]

Glen (Ghurd) is right.  Here is a link to a wire resistance calculator I wrote a while back should it be of use.  I sometimes use it by calculating the resistance for a wire size and distance, and then blanking out the size and changing the units for conversion, or in your case, you can convert to square millimeters or circular mills and then switch it back to guage.  For your case it calculates the cross sectional area of two ten guage wires to be just barely smaller than a seven guage wire.  

http://www.fieldlines.com/story/2004/11/27/12326/032

(holy cow, I wrote that almost 4 years ago, time sure does fly)

Running multiple parallel runs might give you issues with inspectors should that ever be necessary.  I am fairly certain that each line connected in parallel would have to have its own overcurrent protection, but rules vary by location.  Rich