Mike Dolt Enterprises
Mike Dolt Enterprises
User: encoreman, Location: Austin, TX
Asked on: Wednesday, April 20, 2011 at 12:16 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:26 am EDT
Question: I just got comments back from the electrical inspector:SHOW COMPLIANCE WITH NEC 2008 ARTICLE 240.21 YOUR SECONDARY TAP CONDUCTOR OF500KCMIL IF FUSED AT 400AMP AS 240.21 REQUIRES YOUR SECONDARY CONDUCTORS TOMEET OR EXCEED THE SECONDARY OVERCURRENT DEVICE.I have a 480-120/240 v 75 kVA transformer with 500 kcmil conductors. I have 200A fuses on the disconnect on the primary side. There are 400A fuses in the disconnect between the transformer and the panel.The loading on the panel is 236 amps at 240 volts.I'm using Mike's "Commercial and industrial Wiring and Raceway Chart". What do I have to do to get in compliance with this inspector?Jack
NEC 2008 Article 240.21 Requirement
NEC 2008 Article 240.21 requires secondary conductors (between the transformer and panel) to meet or exceed the rating of the secondary overcurrent device (fuses in this case).
Current Situation
Secondary conductors: 500 kcmil Secondary overcurrent device (fuses): 400A
Compliance Issue
500 kcmil conductors are not sufficient for a 400A secondary overcurrent device according to Mike's chart.
Corrective Action
To comply with the inspector's requirement, you need to
increase the size of the secondary conductors to 750 kcmil. This will ensure that the conductors are rated for the 400A fuses.
Note:
Since you have a loading of 236 amps at 240 volts on the panel, 750 kcmil conductors are still sufficient for this load as well. Flag for review