Re: Copper gauge/ OT

[BFDEIHL@aol.com]

Sometimes it's hard to tell when somebody is kidding, over the net.  The 
"economics" of running the smallest proper guage wire is a real world 
consideration when you are planning a building install, but so is the Vdrop 
calc.

The lower the applied voltage, and the higher the amp load- the more 
significant the effect of voltage drop in a conductor.

The math:

for copper conductors- (rule of thumb equation)

25.8, times distance to load in feet, times amp load-divided by conductor 
cross-section in cir. mil.= Vdrop

#2 ga wire- 66360 cir mil (ref. table 8 NEC)
#6 ga wire- 26240 cir mil

Considering a 90A load, and 15 feet from battery to load

25.8*15*90/66360 = .52 V drop (#2 ga)
25.8*15*90/26240 = 1.33 V drop (#6 ga)

In this case, using #6 wire gives about a ten percent Vdrop. Not good.

This is why car stereo competitors use huge supply wiring- it's not for 
ampacity, as much as to minimize voltage drop.

Did the math.

Danny

In a message dated 9/23/01 11:01:52 AM Pacific Daylight Time, aa821@acorn.net 
writes:

<< RE:  Wire size/source
 
 Summit racing also offer complete kit with wire/box in variations from OK 
 to show look.  
 
 Ron (aka cheap a ron) had inquired about wire size in replacing batty 
 leads/gorunds and was gonna go gonzo cause he had some free wire.  Well, 
 IMO, once you go past certain level, you are kinda fooling yourself.  
 Attention to terminating the ends (crimping, soldering, anit-corrosive 
 treatment) may be more important in the real world.  Here is Kelvin's law 
 from old Audel's:
 
 The mnost economical cross-section of a conductor is that for which the 
 annual cost of energy wasted is equal to the interest on that portion of 
 the capital outlay, which can be considered proportional to the weight 
 of hte copper used.
 
 Area of copper conductor (circ. mils)= 593*I[(cost of elect*hours)/wire 
 cost*interest]**1/2
 
 Where I=amp for h hours/year
 wire cost = dollars/lb
 interest = annual percent interest, including depreciation and taxes
 2g=257.6 cir mils;0.1591 ohms/1000 ft
 6g=162.0 circ mils; 0.403 Ohms/100 ft
 
 Do the math.
 
  -- Brian D./OH
 How can you be in two places at once when you're not anywhere at all...
 Firesign Theatre
 
 q
  >>

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