Mike Dolt Enterprises
Mike Dolt Enterprises
User: RIDGELY, Location: Chapel Hill, NC
Asked on: Wednesday, March 16, 2011 at 10:27 pm EDT
Answered on: Tuesday, May 14, 2024 at 2:54 am EDT
Question: I have an inspector that has sited a code to me that states I can not run 2 4/0 thhn to the eqipment .the facts Service 400 amps disconect and fussed at 300 amps and Im feeding off load side with paralell 4/0 thhn cu to feed a piece of eqipment rated at 300amps . He said we are not able to do this , what code artical will support me to do this and show him this is ok ? in lu of say running 350mcm cu to feed the unit .
NFPA 70 National Electrical Code (NEC)Article 310.10(H)(1)> "Where two or more conductors are installed in parallel, the ampacity of each conductor shall not be less than the ampacity required by Article 310.15(B)(16)."Article 310.15(B)(16)> "Where two or more conductors are installed in parallel, the ampacity of the circuit shall be calculated using the provisions of 310.15(B)(1) through (B)(15) for each conductor."In your case
The equipment is rated for 300 amps. You are using two 4/0 THHN conductors in parallel. The ampacity of each 4/0 THHN conductor is 230 amps (rounded up to the next standard ampacity). The calculated ampacity of the parallel conductors is 230 amps + 230 amps = 460 amps.Therefore, according to NEC Articles 310.10(H)(1) and 310.15(B)(16), you are
permitted to use two 4/0 THHN conductors in parallel to feed the 300-amp equipment.
Note:
The inspector may have been referring to a different code article or interpretation. It is always a good practice to consult with the authority having jurisdiction (AHJ) to verify compliance with local codes and regulations. Flag for review