Mike Dolt Enterprises
Mike Dolt Enterprises
User: ammklq143, Location: Iowa
Asked on: Tuesday, April 5, 2011 at 11:07 am EDT
Answered on: Tuesday, May 14, 2024 at 3:47 am EDT
Question: I have a bid I'm working on for a customer that's building a big shed. I originally sized the conductors at 250MCM aluminum because the conductors were going to be about 400 feet long. Now, he says it's ok to put the panel on the other end of the shed, so the total length would be around 300 feet. It's a 200 amp service, but most likely the load would probably never exceed 100 amps. Mostly lighting. 20-6 lamp flourescents, an air compressor occasionally, a welder occasionally, etc.Here's my question. If I use the 3% voltage drop for 120 volts, I can have a drop of 3.6 volts, so that would put the acceptable voltage at 116.4 volts. Ok....so his true voltage is around 124 volts. Do I use the 116.4 volts as the threshold? I would think so, because it's the acceptable level. When I do my calculation for conductor size, can I use 7.4 volts instead of 3.6 volts.
Voltage Drop Threshold
Yes, you should use the acceptable voltage level of 116.4 volts as the threshold for determining the conductor size. This ensures that the voltage drop will not exceed 3% and that the voltage at the end of the circuit will remain within the acceptable range.
Conductor Size Calculation
You cannot use 7.4 volts in your calculation for conductor size. The voltage drop formula considers the voltage drop over the entire length of the circuit, not just the acceptable voltage drop threshold. Therefore, you should use the full voltage drop of 3.6 volts in your calculation.
Suggested Conductor Size:
Based on your description of the load and the estimated length of the circuit, 250MCM aluminum conductors are still appropriate, even with the reduced length of 300 feet. This will ensure that the voltage drop is within the acceptable range and that the conductors can handle the potential load. Flag for review