Main service check
Load calculation for the house plus the casita, by the NEC optional method or from measured demand. If the service cannot carry both, you find out at design, not at inspection.
Run the load calculator →Casita, ADU & Home Addition Electrical in Tucson, AZ
Tucson loosened its casita rules in 2023 and a lot of backyards have a project in them now. Electrically, a casita is a second dwelling: it needs its own load calculation, a feeder and subpanel with a disconnect at the building, its own grounding electrode system, and often a bigger main service to carry both. Arizona Electrical Solutions is a licensed electrical contractor (ROC CR-11) and a licensed mechanical contractor (ROC CR-39), so the casita’s power, its mini-split and the main-house service upgrade are one scope. Check the main service first with the free load calculator.
What It Involves
A casita is a feeder, a subpanel and a load calculation
The building department treats an accessory dwelling unit as a dwelling, and so does the National Electrical Code. That means a load calculation for the casita on its own (kitchen, laundry, cooling, water heater), a feeder from the main house sized for it, a subpanel in the casita with a disconnect at the building, and a grounding electrode system of its own because it is a separate structure.
Then the main service has to carry the house and the casita. Many Tucson homes on a 100-amp service cannot, and some 200-amp homes with an EV charger and electric range cannot either. That is the calculation that decides whether the project includes a service upgrade, and it should be done before the slab is poured, not after.
Feeder and subpanel
Conductors sized for the casita’s load and the distance — usually underground in conduit — landing in a subpanel with a building disconnect and its own ground rods.
Trenching we self-perform →Circuits and cooling
Kitchen small-appliance circuits, laundry, bathroom, AFCI and GFCI where required, and the mini-split or heat-pump circuit — installed by the same contractor that sets the equipment.
Mini-splits and heat pumps →Project Types
The four versions of this job
The right electrical scope depends on what is being built. These are the ones we see most in Tucson.
Detached casita
A new structure in the yard. Underground feeder, subpanel with building disconnect, separate grounding electrode, full set of dwelling circuits. The classic ADU.
Garage conversion
The structure exists; the wiring does not. The existing garage circuit is never enough for a kitchen and a bathroom, so a subpanel is almost always added.
Attached addition
A new master suite or a room over the garage. Usually served from the main panel if it has the spaces and the capacity; a subpanel if it does not.
Separate meter
A rental casita sometimes wants its own utility meter. Whether TEP or Trico will allow it depends on the property; it changes the service equipment and we sort it out with the utility early.
One Contractor
Power, cooling and the trench, in house
A casita touches three trades most homeowners hire separately: the electrician for the wiring, an HVAC company for the mini-split, and someone with a trencher for the feeder. We self-perform all three under our own licences, which is the difference between a project with one schedule and a project with three.
It also means the load calculation is done once, by the people installing every piece of load on it.
- ROC CR-11 electrical and ROC CR-39 mechanical held by the same company
- Feeder trenching and conduit with our own equipment
- Mini-split or heat-pump circuit and equipment in one scope
- Service upgrade priced with the casita, not discovered later
- Coordination with your builder or architect on the plans and the permit set
Permits & Utility
The permit is the whole point
An unpermitted casita is the classic thing that surfaces when a Tucson house is sold: the listing says two dwellings and the county record says one. The electrical permit and inspection are what put the casita on the record as a legal unit, and the feeder, subpanel and grounding are the items the inspector checks first.
The utility side matters when the main service changes or a second meter is wanted. TEP and Trico each have their own rules for that, and we handle the request as part of the job.
- Electrical permit with the City of Tucson, Pima County, Marana, Oro Valley or Sahuarita
- Service upgrade and utility disconnect coordinated with TEP or Trico if the main service changes
- Inspection scheduled and met at rough-in and final
- See what is already on the record at your address with the free property lookup
FAQ
Tucson casita and ADU electrical questions, answered
Can my existing electrical service handle a casita?
That is a load calculation, not a rule of thumb. A 200-amp service often can if the house is gas-heated and there is no EV charger; a 100-amp service usually cannot. NEC 220.87 lets us size from your home’s actual measured demand, which is the fairest test. Run our load calculator for a first look, and we will do the real one when we quote.
Does a casita need its own electrical panel?
Almost always. A detached structure needs a disconnect at the building and, for any real load, a subpanel fed from the main house with its own grounding electrode system. A garage conversion with a kitchen and bathroom needs one for the same reason: the existing garage circuit cannot carry a dwelling.
Can a casita have its own TEP meter?
Sometimes. It depends on the property and the utility’s rules for a second service on one parcel, and it changes the service equipment at the house. If you want to rent the casita and bill separately, tell us at the start and we will raise it with TEP or Trico before the design is fixed.
What does the electrical for a casita cost?
The feeder run and the service upgrade, if one is needed, are the two big variables. The panel upgrade cost calculator will give you a Tucson-area range for the service side by address; the feeder and casita circuits are quoted from the plans.
Do you do the mini-split too?
Yes. We hold the ROC CR-39 air-conditioning licence as well as the electrical one, so the mini-split or heat pump and its circuit are one contract with one contractor responsible for both.
Do you work with my builder or architect?
Yes. We coordinate with the general contractor or designer on the electrical plan and the permit set, and we can take just the electrical scope on a casita someone else is building.
Related Services
Work that usually comes with this one
One licensed contractor for the whole job. See everything we do for Tucson homes.
Residential Panel & Service Upgrades
Home panel and service upgrades — 100A to 200A, FPE and Zinsco replacement, permits and utility coordination.
Residential Load Calculator
Whole-house load and service size by the NEC 220.82 method — free.
Home AC & Heat Pump Replacement
AC and heat-pump replacement with the circuit and disconnect — CR-39 and CR-11 under one roof.
Residential Electrician
Everything we do for Tucson homes — panels, EV charging, AC, casitas, rewiring and generators.
Check the service before you pour the slab
Run the load calculator with what the casita will have in it. Then send us the result and your plans, and we will tell you whether the main service carries it and what the feeder involves.
Request a Quote Call (520) 308-6235