Re: When does voltage drop impact any ampacity calculation?
Assuming 120 volts, single phase and 3% voltage drop, I get:
#14 31.8' 15 amps
#12 46.7' 20 amps
#10 49.6' 30 amps
#8 57.8' 40 amps
#6 61.1' 60 amps
[Now let's see Mr. Holt's fine forum goober my fine tabulation up.]
These figures seem painfully low, but, as I've said, they seem to agree with the results from the calculator. If anyone sees any errors in these figures, please speak up.
using same assumptions and 0.9 power factor. I get a 3.42 volt drop at 20A, 120V, #12 awg. 3% of 120V is 3.6 Volts. I calculate you can get to around 49' before you hit 3.6V drop.
The problem is you would never put a continuous load of 20A on a 12 awg circuit fed from a 20 breaker. If you assume that the continuous load in like 80% of the rated current, then you can get a little farther out before worrying about voltage drop. Heres what I calculate for 80% rated current, 120V, 1 phase, 0.9pf
#12 61'
10 68
8 77
6 87
4 105
3 90
2 96
1 103
1/0 114
2/0 113
3/0 120
4/0 124
250 124
300 126
350 128
400 127
500 126
I think the original post may have been asking at what point do have to worry about voltage drop if you have already oversized the wire for the derating factors. In my experience, not very often. If you have been conservative in your load calculations and you have derated the wire (i.e. oversized it) for things like temp, or number of conductors in the conduit, when you go to do the voltage drop calcs, you find you don't have to worry cause your already running #10 125' for a 12A 120V load. The only time I find I have to upsize conductors is when they get up over the 200' length. However, I am pretty conservative with my circuit loads. If you put 13 convenience outlets on a 20A breaker because the code says you can, you may need to be more concerned about the voltage drop. Heck, with diversity you might still be ok....