[R-390] Can someone tell me...

[2002tii]

Barry wrote:

>How much current can 20-gauge (or other gauge) wire handle for 
>normal chassis-wiring applications.  The wire I have is stranded, 
>silver-plated, Teflon-coated stuff (very nice wire).  Looking at the 
>various charts on the internet, the values seem to be all over the 
>place so not sure what to trust.  Perhaps they're based on different 
>A/circular mil -- dunno.

Stranding provides flexibility, but does not do much of anything with 
respect to current-carrying capacity unless the strands are insulated 
from one another, in which case the high-frequency current capacity 
is increased because the skin effect is reduced (Litz wire uses this 
trick).  Silver plating also tends to be helpful at frequencies where 
skin effects predominate.  Neither has much effect at DC and low AC 
frequencies.

Start from the "fusing current," which is about 58 amps for #20 
copper wire.  At this current, you will melt the wire.  There are 
numerous standards for safe current capacity depending on the 
allowable voltage drop and/or temperature rise.  Typically, they 
range from 0.0014 to 0.005 Amp per circular mil.  For #20 copper wire 
(1024 circular mils), this works out to anywhere from 1.5 amps to 
about 5 amps.  Being a conservative designer, I tend to limit #20 
wire to 2 amps or so.

Best regards,

Don