Mike Dolt Enterprises
Mike Dolt Enterprises
User: sfav8r, Location: San Francisco Bay Area
Asked on: Tuesday, April 26, 2011 at 2:45 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:39 am EDT
Question: We are installing a few pole lights. The lights are 150w each and there are three lights. The power is 208v. The distance is 400' and we were planning on running #10. The plans call for #4. Am I out of line thinking this is overkill? The load will draw just over 2 amps. Their logic is that the circuit will have a 20a breaker so the voltage drop should be calculated on a 20a load. I suggested we could solve that problem (which I don't even consider a real problem) by using a smaller breaker, fusing etc.Upsizing to #4 for some POSSIBLE future load that isn't in any kind of plan for the foreseeable future seems a little crazy to me. There is plenty of room to do another pull in the future if they do add another load.
According to the National Electrical Code (NEC), you are correct that #10 wire is sufficient for your application. The NEC allows for a voltage drop of up to 3% on lighting circuits. With a load of 2 amps at 208 volts, the voltage drop on a 400' run of #10 wire would be approximately 0.5%. This is well within the allowable limit.The argument that the circuit will have a 20 amp breaker is not valid. The NEC requires that the overcurrent protection device (breaker or fuse) be sized to protect the wire, not the load. In this case, a 15 amp breaker would be sufficient.Upsizing to #4 wire for a possible future load that is not in any kind of plan is not necessary. If and when the additional load is added, you can simply pull another set of wires.In conclusion, I agree with you that #10 wire is sufficient for your application and that upsizing to #4 wire is overkill. Flag for review