"Is 100 amps enough?" is one of the most common questions we get about older Miami homes, usually right after someone buys an EV, plans a pool heater, or hears from an insurer. The honest answer is that it depends on what the house runs and how much of it runs at once, and there is a standard way to work that out. Here is what the number means, how to find yours, and how the decision gets made.
What the amp rating means
Your service rating is the most current the house is set up to draw from FPL at once. The main breaker (or main disconnect) is sized to protect the service conductors, the meter base and the panel at that rating. A 100 amp service at 240 volts can supply a lot of power, but not unlimited power: when the total of everything running approaches the rating for long enough, the main trips, or worse, parts of the service run hot.
The rating applies to the whole chain. A panel labeled 200 amps fed by a 100 amp main and conductors is still a 100 amp service. That is why "upgrading the panel" and "upgrading the service" are different jobs, as our panel upgrade page explains.
How to read yours
- The main breaker. In most houses it is the large breaker at the top of the panel, separate from the rest, with a number such as 100, 125, 150 or 200 on the handle.
- An outdoor main. Many South Florida homes have the main disconnect in or beside the meter enclosure outside, with the indoor panel acting as a distribution panel. Then the number to read is outside.
- The panel label. The label lists the panel's maximum rating, which may be higher than the main breaker actually installed.
- Paperwork. A 4-point inspection report records total amps.
Look, but do not open anything. If the number is not visible on the handle with the door open, a photo is usually enough for an electrician to tell you.
What sets the minimum
The National Electrical Code sets a floor for houses: under NEC 230.79(C), the service disconnect for a one-family dwelling must be rated at least 100 amps, and above that floor it must be at least the calculated load, as EC&M summarizes. Some insurers set their own floor too: Universal Property & Casualty's Florida binding guidelines (10-24-18 edition) list a minimum of 100 amps. So 100 amps is the bottom, not a target.
When 100 amps is often enough
A modest house with one central air system, gas or a heat pump water heater, and a gas range often sits comfortably on 100 amps. So can many condo units, which are smaller and frequently served by a feeder rated by the building's design.
Where Miami homes get tight
South Florida houses carry loads that run hard and long. Air conditioning runs most of the year, often through long hot afternoons when everything else is on too. Then add the electric loads that are common here:
- Electric water heater and electric range. Each is a large 240 volt load. With central AC, an electric dryer and these two, a 100 amp service can already be close.
- Pool pump and pool heater. A pool pump runs for hours; an electric pool heat pump is another large motor load. See pool electrical requirements.
- An EV charger. A Level 2 charger draws a large, steady load for hours, often in the evening when the AC is still on. See an EV charger on a 100 amp panel.
- Electric tankless water heaters. Whole-house electric tankless units can need several large circuits of their own. The installation manual lists the breakers and wire size, and it is worth reading before buying one for an older house.
- A second AC system, mini-splits or an addition. Each adds a motor load that may run at the same time as the main system.
You often hear about this first as symptoms: lights dimming when the AC starts, or the main tripping on a hot evening. Our guide to lights that flicker when the AC turns on covers what that does and does not mean.
The load calculation decides it
Rather than guessing, an electrician adds up the house's loads under Article 220 of the National Electrical Code, which applies demand factors because not everything runs at full power at once. Our guide to the electrical load calculation walks through the standard and optional methods with a worked example, and the NFPA 70 page is where the code itself lives. The result is a number you can compare to your service rating, with your planned loads included.
If the calculation comes out tight
- Load management. For an EV, a charger set to a lower current, or a system that backs the charger off when the house is busy, can avoid an upgrade. See load management vs a panel upgrade.
- Moving loads to gas or heat pump equipment. Sometimes the cheaper path is a different appliance.
- A service upgrade. A larger service, commonly 200 amps for a house, means a new meter base, main and service conductors, a permit and inspection, and coordination with FPL, which may need to upgrade its own equipment. See when a home needs a bigger service.
Questions people ask
Is a 200 amp service always better?
It gives headroom for future loads, but it is a bigger job. If the calculation shows 100 amps carries what you run and plan to add, there may be no reason to upgrade now.
Can I just put in a bigger main breaker?
No. The main is sized to protect the service conductors and equipment. A larger main on the same conductors removes that protection.
My panel has empty spaces. Doesn't that mean I have room?
Empty spaces are physical room for breakers, not capacity. A panel can have open slots and still be near the limit of its service. See a panel with no room for breakers for the opposite problem.
Does a condo unit work the same way?
The math does, but the feeder to your unit belongs to the building's design, and upgrades involve the association. See condo electrical work in Miami Beach.
Need it looked at?
KRW Electric (EC13012832) troubleshoots and repairs panels and services that are struggling with today's loads in Pinecrest, Coconut Grove, South Miami and Miami Beach, with same-day service when scheduling permits. Call (305) 359-7312 and tell us what you are seeing. We will ask a few questions, tell you whether it sounds urgent, and give you the earliest time we have. Our before you call checklist covers what to have ready, and what happens on a repair visit explains the rest.
Reviewed by Kyle White, KRW Electric Company LLC — licensed electrical contractor EC13012832.
