What is being decided, and by whom
Three things, and they are decided in this order. The size of the service supplying the house. The capacity of the panel that distributes it, including how many spare positions it has. And the circuits: how many, where they go, and what each one serves.
All three are established by a licensed electrical designer or contractor, working to the electrical code adopted in your jurisdiction, and the installation is permitted and inspected. In the United States that code is NFPA 70, the National Electrical Code, and which edition applies is a jurisdictional question with a local answer.
Nothing on this page describes how any of that work is performed. It describes what the decisions are, so that an owner can take part in them at the point when taking part is useful.
Note
Electrical work is a licensed trade and permitted work. Engage a qualified electrical professional and confirm which code edition and amendments apply with the authority having jurisdiction. This page contains no instructions for performing electrical work of any kind.
Service size is a forecast, not a measurement
The service is sized by a calculation the code prescribes, based on the loads the house is expected to carry. That calculation is arithmetic and a professional performs it.
What an owner contributes is the forecast, and it is the part most often got wrong, because it is a statement about the future rather than the present. A house that will acquire electric vehicle charging, a heat pump, an electric range, a workshop, an accessory dwelling or a photovoltaic system has a different profile to the same house today, and adding those later to a service with no headroom is expensive work involving the utility.
The asymmetry is stark. Additional capacity specified before the service is installed costs relatively little. The same capacity added afterwards can mean a new service, a new panel and a utility connection, at a cost measured in weeks as well as money. If there is a single argument for planning generously anywhere in a house, this is it.
Panel capacity, and the value of empty positions
A panel has a rating and a physical number of positions for circuits. Both fill up, and a full panel with a healthy rating is still a full panel.
Spare positions are the cheapest form of future capacity in the whole building. They cost almost nothing at the time and they are what makes a future circuit a normal job rather than a project. Specifying a panel with meaningful spare capacity, and asking your electrical professional to leave it genuinely spare, is a decision worth making explicitly rather than accepting whatever arrives.
Location deserves a thought too. A panel is a piece of equipment that needs clear access for the life of the building, and the position that seemed sensible on a drawing is sometimes behind a cupboard by the time the house is finished. Clearance requirements are prescribed by code and an inspector checks them.
Circuits are decided while the walls are open
A circuit added during construction is a run of cable through open framing. The same circuit added afterwards involves opening finished surfaces, or a compromise route, or a decision to do without.
So this is the moment to be specific about what the house will contain, room by room. Not merely how many outlets, but what will actually be plugged in and where: a home office with equipment, a kitchen with more appliances than the plan shows, a garage that will hold a workshop or a vehicle charger, an outbuilding, an irrigation controller, a future ADU.
The general rule is that each of those questions costs nothing to answer now and a great deal to answer later. Walk the plan room by room with your electrical professional before the framing closes, and do it with the furniture layout in front of you rather than the floor plan alone. The reasoning is the same one running through the front sheet: the decisions that matter are the ones that stop being cheap.
What the inspector is looking at
An electrical inspection is not an assessment of neatness. It checks that what was installed matches what the code requires: that circuits are protected appropriately, that the required protective devices are present where they are required, that conductors are sized for their loads, that boxes and terminations are accessible, and that the whole installation is what the permit described.
Two of those are worth an owner understanding, because they are where questions arise. Protective devices of specific types are required in specific locations, and which ones in which rooms differs between code editions, which is another reason the edition your jurisdiction has adopted is a question worth asking early. [1]
And accessibility is a permanent requirement rather than a construction-stage one. Junctions have to remain reachable, which is why an inspector cares about something that will be behind a wall in a week. If a finish detail would bury one, it is better to discover that at rough inspection than during a renovation a decade later.
Questions
- How large a service should I ask for?
- That is a calculation your electrical professional performs against the loads you tell them about, so the useful contribution is the list of future loads rather than a number. Say what the house may plausibly acquire in the next decade and let the calculation follow.
- Is it worth pre-wiring for things I may never install?
- For a conduit or a cable route, usually yes, because the cost while walls are open is small. For equipment, usually no. The distinction is between leaving a path and buying a thing, and the path is the part that gets expensive later.
Sources
- 1International Code Council. International Code Adoptions. Accessed 2026-08-29