Mike Dolt Enterprises
Mike Dolt Enterprises
User: Alwayslearningelec, Location: NJ
Asked on: Wednesday, April 27, 2011 at 3:25 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:41 am EDT
Question: Ok if I have (4) 20A duplexes spaced about 110' apart being run in conduit and the homeruns must in #10(THHN). How do I know/calculate if #12's would be ok from duplex to duplex? I know there must be a distance where #12's will not be sufficient.They are being fed from a 120/208 panel and a 20a circuit breaker.THANKS VERY MUCH
1. Calculate the total circuit length
110' x 3 (since there are 3 runs between duplexes) = 330'
2. Determine the voltage drop limit
For branch circuits, the voltage drop limit is typically 3% or less.3% x 208V = 6.24V
3. Calculate the resistance of the circuit
Voltage drop = Resistance x CurrentRearranging the formula: Resistance = Voltage drop / CurrentCurrent = 20AResistance = 6.24V / 20A = 0.312 ohms
4. Determine the resistance of #12 and #10 conductors for the circuit length
Resistance of #12 conductor for 330' (from wire tables): 1.95 ohmsResistance of #10 conductor for 330' (from wire tables): 1.21 ohms
5. Compare the resistance of #12 and #10 conductors to the resistance limit
#12: 1.95 ohms > 0.312 ohms (resistance limit)#10: 1.21 ohms < 0.312 ohms (resistance limit)
Conclusion:
Based on the voltage drop limit of 3%, #12 conductors would not be sufficient for the circuit length of 330'. #10 conductors would be required to meet the voltage drop requirements. Flag for review