A 200-amp electrical service is not automatically better for every house, and a 100-amp service is not automatically too small. The right size is a load calculation, not a square-footage guess. For many Sacramento-area homeowners, the real question is whether the existing service has enough capacity for the house now and for the electrical loads they expect to add next.
100A can still be enough. 200A is not automatically better. The right size is a load calculation — not square footage, not the number of breakers, and not “200A because that is what everyone gets now.”
100A vs 200A at a glance
The service rating describes how much current the home’s electrical service equipment is designed to handle. A typical modern residential service is 120/240 volts, single phase.
| Question | 100A service | 200A service |
|---|---|---|
| Typical fit | Smaller home, modest electric loads, gas heat/water/cooking | Several large electric loads at once |
| EV charger | Possible if the calculated load leaves capacity | More headroom; still not automatic |
| Same as the panel enclosure rating? | No | No |
| Decided by | Load calculation | Load calculation |
| Service rating | Approximate capacity at 240V |
|---|---|
| 100A | About 24 kVA |
| 125A | About 30 kVA |
| 150A | About 36 kVA |
| 200A | About 48 kVA |
Those numbers are not the amount of power the house continuously uses. They describe the service’s maximum rating. Electrical codes size a service from a load calculation because household loads do not all operate at full power at the same time, which is why simply adding every appliance’s nameplate rating together usually gives the wrong answer.
Is 100A service enough?
Sometimes, yes. A 100A service can still be adequate for a smaller home with relatively modest electrical loads, especially where major appliances remain gas-fired — gas space heating, gas water heating, gas cooking, no EV charger, no spa, no large workshop equipment, and conventional household lighting and receptacle loads. In that situation, 100A may be completely workable, and it is not out of code simply because it is not 200A.
The problem begins when the house becomes substantially more electric. A service that was reasonable decades ago may have little remaining capacity after several major loads are added.
100A starts becoming restrictive when the home has — or is about to add — several large electric loads: Level 2 EV charging; an electric range or induction cooking; heat-pump HVAC or a heat-pump water heater; electric resistance heating or an electric dryer; a spa, hot tub, or sauna; workshop or large air-conditioning equipment; an accessory dwelling unit or substantial home addition; multiple dedicated 240V circuits; or solar-plus-battery equipment that requires service changes. No single item automatically means the service must be upgraded. The issue is the combined calculated load.
What pushes a home toward 200A?
A 200A service becomes more attractive when the home’s electrical demand is growing in several directions at once. A common example is a house transitioning from gas appliances to electric equipment: a heat pump, a heat-pump water heater, an induction range, an electric dryer, and an EV charger. Each individual project may be manageable. Together, they can change the service calculation significantly.
This is why planning one project at a time can produce bad decisions. If several electrification projects are likely over the next few years, it makes sense to calculate around the future house rather than only the present one.
200A does not mean unlimited. A 200A service provides substantially more capacity than a 100A service, but it is still finite. Large homes can exceed what a conventional 200A service comfortably supports, especially with combinations such as multiple HVAC systems, two EV chargers, large electric cooking loads, pool and spa equipment, detached structures, substantial workshop loads, ADUs, and all-electric space and water heating. In some cases the correct answer is load management rather than a larger service. In others, service above 200A may need to be considered. For SMUD-served properties, service configurations above 200A can involve additional utility requirements and engineering review.
How EVs and electrification change the answer
Electrification is the reason this question comes up so often now. Adding one large electric load rarely settles it; the loads tend to arrive together, and each one draws down whatever headroom the service had.
Does an EV charger require 200A service? No. This is one of the most common misconceptions. A Level 2 EV charger can often be installed on a home with less than 200A service if the calculated load leaves enough capacity. The charger itself can also be configured at different current levels — an EV charging circuit might be designed around 20A, 30A, 40A, 50A, or 60A depending on the vehicle, the charging equipment, the circuit design, and the available service capacity. In some homes, load-management equipment allows EV charging without increasing the service size. In others, the service is already close enough to its calculated limit that an upgrade is the cleaner solution.
So the useful sequence is:
- determine the existing service size;
- calculate the existing load;
- determine the proposed charging load;
- evaluate whether load management is appropriate;
- upgrade the service only if the project actually requires it.
Gas-to-electric conversions add up faster than any single project suggests. A heat pump, a heat-pump water heater, an induction range, and an EV charger each look modest on their own, but they land on the same service. If more than one is on the horizon, size the service for the house you expect to have, not only the one you have today.
How is service capacity actually calculated?
The proper method is a residential load calculation — a calculation, not a rule of thumb. Under Article 220 of the National Electrical Code, a dwelling calculation totals load by category (general lighting and receptacles, small-appliance circuits, the laundry circuit, fixed appliances, cooking equipment, heating and air conditioning, water heating, dryers, EV charging, and other large or continuous loads) and then applies demand factors. Demand factors exist because, as the code’s dwelling-calculation rules recognize, there is load diversity — not every connected load runs at full rating at the same time. Trade references put the same point plainly: sizing a service “isn’t simply a matter of totaling the loads or breaker ratings.”
There is more than one recognized approach — a standard method and an optional method — and which demand factors apply to which loads involves judgment. That is why the honest answer to “what size do I need?” is a calculation for your specific house, not a universal formula off the internet.
Does square footage decide it?
No. “Your house is 2,000 square feet, so you need 200 amps” is not how it works. Floor area does feed the general-lighting portion of the calculation, and larger houses often contain more electrical equipment, so house size matters indirectly. It is not the deciding rule.
Why counting breaker handles doesn’t work
A panel can contain breaker ratings that add up to far more than the service rating, and that is normal. A 200A panel might hold breakers whose face values total 500A, 700A, or more. That does not mean the home is overloaded — branch-circuit breakers protect individual circuits, and the system is designed around expected demand, not the mathematical sum of every breaker handle. The correct question is not “Do all my breakers add up to more than 100 amps?” (they almost certainly do). It is whether the home’s calculated demand is within the service capacity.