I am working with the city to get the permits to build an outdoors kitchen with its own sub-panel. I decided to place it 100ft from the house. In my list[*] I have an electric tankless water heater, an induction range and a hot-tub/spa (all 240V), plus a bunch of occasional 120V devices (food processor etc) and LED lights. After some research on those loads I want to size the wiring for 150A, the great majority of which will be 240V loads.

So far my plan includes 2in sch40 PVC conduit to house the wiring in the trench. How do I calculate the (aluminum) wiring size and what cable is appropriate for buried conduit? Thank you

[*] The comments asked to provide a list of my desired loads for this load center as to validate my requirements. Keep in mind this outdoors kitchen is designed to feed parties of 40 people:

  • It would be good if answers discussed the neutral size, and under what conditions it would be permissible to downsize the neutral. Jan 11, 2020 at 9:27
  • Can you post the rated wattage/amperage for the spa, heater, and range? Also, how many amps is your main service? (That second water heater has me concerned some...) Jan 11, 2020 at 14:52
  • A point of use water heater I use for cases like this is only 30a 240v it brings water up to 135/140 degrees for a single tap with moderate flow. But I agree we need the sizes to calculate the feeder even with a spa it sounds like the op just added the sizes with no derating as may be allowed.
    – Ed Beal
    Jan 11, 2020 at 17:06
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    @AlessioSangalli you have to run the load calculations recursively, all the way up to the service, every time you do a load calculation -- imagine what'd happen if you had a 200A service trying to service this big kitchen feeder + an entire all-electric house with stuff going as well... Jan 11, 2020 at 22:26
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    @ThreePhaseEel the main breaker is a 200A and I am actively working with the city and power company to upgrade it to 400A. I have the appointment tomorrow morning. There will be a meter / panel combo that will go to different load centers, including one in this outdoors kitchen. I wish I had three phase power for the workshop where I have the mill and lathe, but I'll have to continue with single phase VFD's. As that part of the job is actively being worked on, I was trying not to bring it in the discussion. Jan 13, 2020 at 3:50


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