Minimum Main Panel Size/Service for Tiny Homes (e.g. 150sf)

[brycenesbitt]

I'm working in California where the minimum size for a residential unit is 150 square feet, when developed
as a backyard cottage.

However at present time the electrical, energy and building codes are set for larger structures.

What do people feel is a reasonable practical minimum for a 150 square foot residence, all electric, with and without
potential for EV parking? What does the code say in various places --- are there any local relaxation for the tiny homes?

These almost all have: kitchen convenience outlets, stove, heat, bathroom, maybe AC
They almost always share: water heating, laundry, EV charger, solar.

Past discussion: https://forums.mikeholt.com/threads/minimum-residential-electric-size-by-code.74028/

 

[pv_n00b]

There has been a lot of work on local codes related to tiny homes, ADUs, etc. But right now it's a mishmash with some AHJs being very progressive and others not at all. It's going to depend a lot on where you are and what your local AHJ has done to make the codes and standards more applicable to the requirements of small residential units.
The NEC has a minimum service disconnect rating for a single family residence of 100A, 3 wire (230.79(C)). Your local utility may have a higher minimum service drop. What is reasonable? Do the load calculation in NEC 220 and see what you come up with. Probably much less than 100A. Just because you have to have a 100A service disconnect does not mean you have to use all that power, you just have to have a 100A panel.
Good luck with your projects, I'm a tiny house and ADU proponent.

 

[tom baker]

For many years the NEC min size service was 60 amps. But your tiny house may use a feeder then it could be smaller

 

[suemarkp]

225.39(C) still says 100A disconnect for a one family dwelling, but it doesn't say the feeder has to supply 100A. If these have a kitchen, a range, and HVAC, I think it would be tough to get much under 60A. Get rid of the range and give them a toaster oven and hotplate, then you could go smaller.

I would think trying to cool a tiny house while an electric oven is being used could be difficult. I see the oven as the biggest problem.

 

[synchro]

I would think trying to cool a tiny house while an electric oven is being used could be difficult. I see the oven as the biggest problem.

They need a little attached cookhouse like in the old days.

 

[NTesla76]

Actually it says rated for 100 amps. So technically, couldn't you have a disconnect rated for 100 amps, but have a lower OCPD installed?

 

[brycenesbitt]

Is there anything useful in the code for apartments: often these are more like extra units, rather than full homes.
Heat is gas wall, or electric mini-split. In our local area gas is only allowed in retrofit situations.