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	Subject - Conductor calculations veganfan I had to figure out some conductor sizes for school and came up with this. conductor calculations LOAD SUMMARY 208Y/120 3Phase 4-wire Computed OCPD Continuous load 20,000VA 25,000VA Noncontiuous load 12,000VA 12,000VA Highest motor load 8,000VA 10,000VA Other motor loads 16,00VA 16,000VA Growth 2,000VA 2,500VA Total Computated laod & OCPD load 58,000VA 65,000VA OCPD Selection Input Output OCPD Load Volt-Amperes & Amperes 65'00VA 314.90A OCPD Rating 350A Minimum Conductor size 500mcm(thwn) Minimum Ampacity 301A Phase Conductor Selection Input Output Ambiet temp & Correction Factor 43C 0.82 Current Carrring Conductors & Adjustment Factor 4 Conductors 0.8 Derating Factor 0.82 * 0.8 = 0.656 Minimum Allowable Ampacity 301/0.656 = 458.84A Conductor Size THWN 700MCM Conductor Type Allowable Ampacity 460A * 0.656 = 301.76 Voltage Drop per 1000ft 0.9pf 3PH 254.81*180ft*.68/10^6 =0.312V .312V/208V =.15% Neutral Conductor Selection Input Output OCPD Looad Volt Amperes 65,000VA Balanced Load Volt-Amperes -24,000VA Nonlinear Load Volt-Amperes +20,000VA Total Load Volt-Amperes 61,000Va Minimum Neutral Size THWN 3/O Minimum Allowable Ampacity 61,000VA /208V =369.59A Neutral Conductor Type & Size THWN 250 MCM Allowable Ampacity 405.000 405 * 0.656 = 324 BUT THIS SEEMS WAY TO LARGE WHERE DID I GO WRONG? wareagle Total Load continous 20000 x 1.25 = 25000 Noncontiuous load 12000 High mtr load 8,000 x 1.25 = 10000 Other motor loads 16000 Total 63000 va YOU FORGOT TO DIVIDE BY SQRT OF 3 63000/(208X1.73) = 175 amps assuming your figures are correct Ambiet temp & Correction Factor 43C 0.82 WHY AMBIENT CORRECTION? Current Carrring Conductors & Adjustment Factor 4 Conductors 0.8 Derating Factor 0.82 * 0.8 = 0.656 Minimum Allowable Ampacity 175/0.656 = 267A If you insist on temp correction Suggest a 400 amps service min. Since you have harmonic loads use 4 500kcm copper for phase and neutral veganfan Thanks for help. I was not sure about the three phase correction of 1.73 becouse part of load single phase. As far as ambient temp correction factors I got this from table B.310.1 in annex B. Is this wrong? wareagle The tables in 310.16 are for 30C or 86F. If you have something other than this temp you must derate. What is the temp of you project? veganfan The ambient temp was given to us at 43c or 110f. We had to find the derating factor. I thought i found in correct table, but if I am wrong please let me know