Below you will find a picture of Annex D example 7 from the 2017 NEC pages 799/800. It was put back in the Code to do away with the confusion that was created when they took the table out of the Code book and made it into a calculation. To many inspectors, plan reviewers, engineers, and architects have been wrongfully applying this section of the Code for a while now. I get numerous calls and emails about having to use 3/0s for a 200a service when in the past we used 2/0s. I only use the 200a service as an example. The Code panelists never meant to make it so difficult to figure out what they wanted, but unfortunately they did. When they made it a calculation they did not change the sizes of the wires in the table they just made it into a calculation, that for some reason we’ve had a tuff time understanding. As long as the load calculation does not exceed 200a the 2/0s are the conductors needed to feed a 200a service. This method works for all services of a100a on up to and including a 400a service So in the 2017 NEC they placed the residential table back in the Code back in Annex D. Probably the most misunderstood part of this Code section is that the conductors being used will have a load calculation that is above the ampacity of the conductor involved. Maybe the Code panel should include this section with the other conductor applications listed in 240.4(G).
If you have any comments or questions about this change please email me at jleccemail@hotmail.com
Can’t see the whole slide just click on it.
Till next time be safe work safe.
Jake