The Space Heater, the Microwave and the Breaker That Quits
It is a cold January evening. The space heater is running, someone starts the microwave, and the basement goes dark. You reset the breaker and wonder whether the house simply cannot keep up anymore.
Sometimes that is a sign of a bigger question: 100 amp vs 200 amp service, and which one your home actually needs. The answer depends on what you run, not on the age of the house alone.
What 100 Amp vs 200 Amp Service Means
Your service size is the most current your home can draw from DTE’s lines at one time, measured in amps. It is set by the wires that come into your meter base, the meter base itself and the main breaker in your panel. All three have to match.
A 100 amp service was a sensible size for decades. It handled lights, a refrigerator, a range and a dryer. A 200 amp service simply doubles that ceiling, which matters once electric heating, charging and cooking enter the picture.
Bigger is not automatically better. A modest house with gas heat and no big electric plans can live happily on 100 amps.
How to Check What You Have
You can find your service size in about a minute, without opening anything.
- The main breaker. Look at the large breaker at the top of the panel. The number on its handle (60, 100, 150 or 200) is your service rating.
- The rating label. A sticker inside the panel door lists the maximum amperage.
- A fuse box. Screw-in fuses usually mean an older 60 amp service.
- The meter base. Some meter bases carry a rating on a label or on the metal.
Keep in mind that the main breaker can be larger than the wires behind it. If a previous owner swapped a panel without updating the meter base and service cable, the label may promise more than the house can deliver. Our guide to understanding your electrical panel shows where each part lives.
When 100 Amp Service Is Still Enough
A 100 amp panel is not a defect. Plenty of Washtenaw County homes run well on it for years, especially when gas handles the furnace, water heater, dryer and range.
The way to know for sure is a load calculation. It is a standard method from the electrical code that adds up the square footage, the fixed appliances, the heating and cooling, and anything new you plan to add. It shows how much of your 100 amps is already spoken for.
Sometimes the result is good news. A single Level 2 charger, or one new circuit for a workshop, may fit with room to spare. Other times a home that looks fine turns out to be near the limit before the new project is even added.
Signs It Is Time to Move to 200 Amp Service
A pattern of small problems often points to the service size, not to a bad breaker. Watch for these:
- Breakers trip when a few large appliances run together
- Lights dim when the furnace, dryer or heat pump starts
- The panel is full, or has doubled-up breakers where one slot was meant to hold one
- You are adding an EV charger, heat pump, induction range or hot tub
- You are finishing a basement or building an addition
- The meter base is rusted, loose or damaged
- You still have a fuse box or an old panel with a poor track record
That last point matters for safety, not just capacity. If your panel is a Federal Pacific or Zinsco, see our page on replacing Federal Pacific and Zinsco panels. Replacing a questionable panel is a natural moment to size the service for the next twenty years.
EVs, Heat Pumps and Hot Tubs: What Pushes a Home Past 100 Amps
Three upgrades come up again and again in Ann Arbor homes.
A Level 2 EV charger can pull 40 or 48 amps for hours at a stretch. That is a big slice of a 100 amp service, especially at dinner time when the range is on.
A heat pump needs its own circuit and runs hardest on the coldest nights, which is when the rest of the house is busiest too.
A hot tub or sauna adds a large 240 volt load that tends to be the last straw. Any one of these might fit with careful planning. Two or three together usually call for a 200 amp service upgrade.
What a Service Upgrade Involves
An upgrade replaces more than the box on the wall. A full job usually covers the panel, the meter base, the service entrance wires, and grounding and bonding to current code. On overhead service, we also check the mast and the weatherhead where the utility lines attach.
The utility handles its side of the work. DTE disconnects power so we can work safely and reconnects it once the work passes inspection. We coordinate that visit and pull the permit, so you are not juggling calls.
It is also a good moment to add a whole-house surge protector at the new panel, and to leave labeled space for a generator inlet or transfer switch if you want one later. For a closer look at how the panel itself differs from the service, see our electrical panel upgrade page.
Getting an Honest Answer for Your House
The simplest next step is a walkthrough. We look at your panel, meter and service, run the load calculation and tell you plainly whether 100 amps still works or whether 200 amps is the better fit. If your house does not need an upgrade, we will say so.
Our crew has been working in Ann Arbor since 1994, and our electricians are union trained through IBEW Local 252. Estimates are free, and our pricing is time and material with no scheduling fee. To set up a visit, contact us.