Can someone give me a formula or a reassuring statement regarding the facts on voltage drop, on a circuit that includes different sizes of wire. I'm on a job where the spec is anything over 250' on 277v branch circuits must be upsized from #10 to #8. The problem I'm running into is some say that you can pull the first 250' in #8's and the rest of the length in #10's. Or pull #8's to the last J-box if it's over 250' and then run a mc whip in #12's. Any comments would be appreciated thank you.
Another VD question
- Thread starter ggonza
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You can do that as long as you have the right overcurrent protection for the #12 wire.
SG-1
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- Ware Shoals, South Carolina
Running the first 250ft with 8AWG will reduce the volt drop for the entire circuit. You have to calculate the volt drop to the end of the 8 AWG. Then using the remaining voltage calculate again to the end of the 10 AWG.
Here is a nice volt drop calculator.
http://www.electrician2.com/calculators/vd_calculatoradv.htm
Here is a nice volt drop calculator.
http://www.electrician2.com/calculators/vd_calculatoradv.htm
You should ask for clarification of the spec. My suspicion is that the intent is to run #8 the whole distance for runs over 250'. Are the "some" who say it's OK to use #10 part way authorized to interprete the specifications?
You could use formulas or a voltage drop calculator to see what the voltage drop would be for 250' of #8 and the rest at #10. What load do you use? What power factor? What voltage drop limit? You may make what you think are reasonable estimates of these, but does it meet the spec?
It does not sound like you got it. If the ckt is over 250 ft you must use #8 for the entire diistance of the ckt. You may tap it with #12 MC but no #10 is used.
when I said I understand it. I meant that I understand the effects of voltage drop when using different sizes of wire. I know that to stay in spec I would still need to use the larger size of wire for the entire length of the circuit. And only use a smaller size for a tap to a utilization device that is not suited to handle the larger size.
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