From: nojunk@knology.net   
      
   On 9/6/2018 9:05 AM, Andy wrote:   
   > I looked at an ampacity table but it was confusing.   
   >   
   > Would a 4 ft. length of 18 AWG wire be ok for a 10 amp load.? (Circular saw)   
   >   
   > Thanks,   
   >          Andy   
      
     I have to assume when you saw 4ft that when we do the calculation we   
   need to use 8 ft, because the current flows through both the hot and   
   neutral wire.   
     18 gauge copper wire has 6.385 ohms of resistance per 1000 ft.   
   If you divide 8ft by 1000ft you get 125.   
     So if we divide 6.385 ohms by 125 we get 0.05108 ohms.   
   Voltage drop is current times ohms. 10amps x 0.051 = 0.51 volts.   
   Then from your 120Vac line the ft cord will drop to 119.49 Volts.   
     I don't consider that a problem, but note, the manufacturer did!   
     What did they use 16 guage?   
   If you consider a 50ft 18 gauge extension cord, that would cause a   
   6.385v drop leaving you 113.15v, (you can subtract 0.51 for you 4ft   
   cord) starting to have some concern, but it will work unless you put a   
   heavy load on the saw. If you put a very heavy load on the saw and draw   
   20 amps, now you are down to 106.2v.   
     Now start thinking about your home, is there 50 ft of 14gauge wire   
   from the breaker box to the outlet. That add another 0.25 ohms in the   
   circuit, that will add another 2.5v drop at 10 amps and 5v drop if you   
   draw 20 amps.   
     Adding all those together and using your 10 amp number,   
   0.051 + 0.6385 + 0.25 = 0.9395 ohms, you're losing about 1v per amp.   
     I hope that gives you some insight.   
      
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