Mike Dolt Enterprises
Mike Dolt Enterprises
User: HVACRMAN, Location: Phoenix, AZ
Asked on: Friday, April 17, 2009 at 1:06 pm EDT
Answered on: Sunday, May 12, 2024 at 4:58 pm EDT
Question: Scenario:Applicant freezer commercial RLA is 12-13 115V 220-230ft run. electrican ran 10ga for 200ft then used 12ga wire for the last run 20-30ft. the compressor is over heating and taking out the start relays. voltage drop at LRA is 90volts. I keep telling the owner the wiring is too small for the length of run. and she doesn't belive me. I did my own load calucation and it confirms the wire is too small and should be using a 6-8ga wire continuos run with NO break or smaller size wire in between runs.originally the run was 12ga @220-230ft burnt out my start relay start cap & runcap I replaced the starting compnents. I explaned to the owner the wire is too small. the electrician rewired the circuit to 10ga but hear this THE GUY HALF ASS went 200ft then RE-USED 12ga the last 20-30ft. The freezer ran better, but not good enough. I went back the 3rd time and it burnt out the start relay, start cap & run cap again. I have since voided out the warranty because of the continous problem of wire size too small. & to top it off 2 different wire sizes. any damage should be paid by the electrician or the electrical engineer who sized it.will someone qualitfied help me out? I've talked tp several professional and they all agree the length is too small but she says her people are right. the numbers I input on the calulations DON'T LIE, I keep telling her (as I'm bang my head against the wall).
Electrical Calculations
Voltage Drop Calculation
Using the following formula:
For 10 AWG wire: Resistance (R) = 0.0056 Ω/ftFor 12 AWG wire: Resistance (R) = 0.0089 Ω/ftVoltage Drop (V) = Length (ft) Current (A) Resistance (Ω/ft)
Current Calculation
Using the freezer rating: 12-13 A at RLA (Running Load Amps)
Load Calculation
For 10 AWG wire (200 ft) + 12 AWG wire (20-30 ft)
Voltage Drop (200 ft) = 200 ft 12.5 A 0.0056 Ω/ft = 14 V Voltage Drop (20-30 ft) = 25 ft 12.5 A 0.0089 Ω/ft = 2.7 V Total Voltage Drop = 14 V + 2.7 V = 16.7 V
For Continuous 6-8 AWG wire (220-230 ft)
Voltage Drop = 220 ft 12.5 A 0.0045 Ω/ft = 11.9 V (for 6 AWG) Voltage Drop = 220 ft 12.5 A 0.0077 Ω/ft = 20.6 V (for 8 AWG)
Conclusion
Based on the load calculations, the following conclusions can be drawn: The voltage drop using 10 AWG wire followed by 12 AWG wire is excessive (16.7 V), which is significantly higher than the allowable 5% (5.75 V). Using a continuous 6-8 AWG wire would significantly reduce the voltage drop, making it within the acceptable range.
Recommendations: The electrical wiring should be replaced with a continuous run of 6 AWG or 8 AWG wire to minimize voltage drop and ensure the proper operation of the freezer.* The electrician or electrical engineer responsible for sizing the wiring should be held accountable for the incorrect sizing and any damages incurred due to overheating. Flag for review