A solar quote comes back with a recommendation to upgrade to 400-amp service. Or an electrician assessing your panel says you'll need 400 amps to run the new heat pump plus your EV charger. The number sounds authoritative — and at $4,000 to $8,000 installed, it should be. But most homes that get quoted a 400-amp upgrade don't actually need one.
The honest answer comes from a load calculation, not a gut feeling about "future-proofing." This guide explains what a 400-amp service is, which homes genuinely require it, what it looks like when one is installed, and how to evaluate a contractor's recommendation before you commit.
A 400-amp service is appropriate for homes with simultaneously high electrical loads: multiple heat pumps, two or more EV chargers running overnight, whole-home battery storage, and a large all-electric kitchen. If your home runs on a mix of gas and electric, or you're adding solar and a single EV charger, a 200-amp service is almost certainly sufficient.
What a 400-amp panel actually is
Most homeowners picture a 400-amp panel as one giant breaker box — twice the size of what they have now. That's not quite right. In practice, a 400-amp service means your home gets twice the electricity coming in from the street, and that power typically splits into two separate 200-amp panels inside the house. Think of it as two normal panels running side by side off a shared power supply.
On the outside of the house, there's a meter and usually a main disconnect — sometimes combined in one enclosure, sometimes separate. Depending on your utility company, they may also require a second box called a current transformer cabinet alongside the meter. It's roughly the size of a small toolbox bolted to your exterior wall, and it's a detail many homeowners aren't warned about upfront. If your electrician quotes you 400-amp service and doesn't mention whether your utility requires one, ask.
Who genuinely needs one
A 400-amp service is justified when a load calculation — not a headcount of how many things you own — shows that your home's simultaneous electrical demand consistently approaches or exceeds what 200 amps can supply. That's a relatively short list of scenarios:
All-electric homes with multiple high-draw systems running simultaneously. The classic case is a large home that has eliminated gas entirely: electric heat pumps for heating and cooling, an electric tankless water heater, an induction range, a dryer — all with the potential to run at the same time. A single 200-amp service handles roughly 48,000 watts at full capacity. Electric tankless water heaters alone can draw 24–36 kW. Add a heat pump and a dryer and you're close to the limit before anything else turns on.
Multiple EV chargers operating overnight. A Level 2 charger draws 40 amps (50A circuit) while charging. One charger on a 200-amp panel is no problem. Two charging simultaneously draws 80 amps — still manageable if your other loads aren't also peaking. Three or more chargers running simultaneously is where a 200-amp service starts to strain. Two chargers plus a heat pump plus a hot tub is where electricians start running the numbers seriously.
Solar plus whole-home battery storage. Solar panels alone don't require 400-amp service — most residential systems connect to a standard 200-amp panel without issue. Where it gets complicated is when you're also adding a large battery bank that powers your whole house during outages, and you want to charge electric vehicles from that stored energy at the same time. That combination of generation, storage, and heavy consumption is where a 200-amp panel starts to hit its limits and 400 amps genuinely earns its place.
Additions that create effectively two separate households. A large home addition, an accessory dwelling unit with its own full kitchen and laundry, or a detached guest structure with significant electrical needs — when the combined load of the main structure plus the addition pushes past what a single 200-amp panel can supply, 400 amps handles both under one service entrance rather than pulling a second meter.
A load calculation takes an electrician about 30 minutes and tells you definitively what service size your home needs. Get matched with licensed electricians in your area who can assess your current panel and run the numbers.
Who doesn't need one — and why contractors sometimes recommend it anyway
Not every contractor recommendation for 400-amp service is wrong — but some are based on habit or upsell rather than your actual electrical load. Here's what doesn't justify the upgrade, so you know what to push back on.
"You're out of breaker spaces" is not a reason for 400-amp service. This is the most common misapplication electricians on trade forums repeatedly flag. A 200-amp panel with only two open breaker slots doesn't mean your service is undersized — it means you might benefit from a sub-panel. A tandem breaker or a small sub-panel fed from the existing panel costs a fraction of a 400-amp service upgrade and solves the space problem without touching the meter or requiring utility coordination. See our sub-panel vs panel upgrade guide for how to evaluate that decision.
Adding one EV charger is not a reason. A 50-amp circuit for a Level 2 charger is a straightforward addition on most 200-amp panels, assuming available load capacity. The EV charger does not add 40 amps of continuous draw on top of your existing loads — it's the charger's dedicated circuit, and most homes have enough unused capacity on a 200-amp service to accommodate it without any panel work. Read the full breakdown in our EV charger panel upgrade guide.
Solar installation alone is not a reason. A residential solar array — even a 10 kW system — connects to your existing 200-amp panel via a backfed breaker. The NEC's 120% rule limits solar backfeed to a specific calculation based on panel bus rating, but most standard residential arrays land within that limit on a 200-amp service. It's the combination of large solar plus battery storage plus high-load appliances that starts to justify looking at 400 amps.
"Future-proofing" without a load calculation is speculation. Some contractors recommend 400 amps as a hedge against everything a homeowner might add over the next decade. That's not necessarily bad advice if your situation genuinely warrants it — but it should come with the load calculation to back it up, not a general sense that "you'll want room to grow."
What actually gets installed
A 400-amp upgrade is a bigger job than a standard panel swap — and that's part of why it costs more.
The utility company runs heavier cable from the street to your home to handle the increased power. On the exterior, the electrician installs a new meter enclosure and a main shutoff. Some utility companies also require a separate metering box alongside the meter — if yours does, that's an extra piece of hardware on the side of your house that adds to the cost.
Inside, you'll end up with two breaker panels instead of one. Each panel is a standard 200-amp box. Your existing circuits get divided between them, and any new circuits go into whichever panel has room. It sounds complicated, but from a day-to-day living standpoint you'd barely notice — the light switches and outlets work exactly the same way they did before.
One thing that's not in the electrician's control: the utility company has to physically disconnect your power before work starts and reconnect it after inspection. In busy markets, that reconnect appointment can take a week or more to schedule after the electrician is done. It's worth asking about the local timeline before you book the work.
Cost and what drives it
A 400-amp service upgrade typically costs between $3,500 and $8,000 installed, with the wide range driven by four main variables.
Whether your utility requires an extra metering box. Some utility companies require an additional enclosure on the exterior wall — called a CT cabinet — when you go to 400-amp service. If yours does, expect to add $500–$1,500 to the job. Ask the electrician upfront whether your utility company requires it; they'll know.
Where the meter is relative to your panels. A meter on the garage wall feeding panels five feet away is a simple run. A meter on one side of the house feeding panels on the opposite end, through a finished basement and up a floor, adds hours of labor and more materials. The distance and route matter more than people expect.
The panels themselves. Two new 200-amp breaker boxes plus the main enclosure at the meter runs roughly $800–$1,500 in hardware before labor, depending on brand and how many circuit slots each panel needs.
Where you live. Electrician labor costs vary more by region than almost any other home service. The national median electrician wage was $62,350 in 2024 per the BLS, but the real range runs from under $40,000 in rural markets to over $100,000 in high-cost cities. The same job costs meaningfully more in Seattle or San Francisco than it does in rural Tennessee. For full cost ranges by region and job type, see our electrical panel upgrade cost guide.
Get matched with licensed electricians in your area who handle service entrance upgrades. They'll assess your current setup, run a load calculation, and tell you whether 400 amps is actually required — or whether a less expensive option handles your needs.
The permit and utility process
A 400-amp service upgrade always requires a permit — no exceptions. The permit triggers an inspection by your local building department once the work is done, and the utility won't reconnect your power until that inspection is signed off. Skip the permit and you're stuck without power until you either get it retroactively approved or tear the work out. It also creates problems with homeowners insurance if something goes wrong down the road.
The general sequence: the electrician pulls the permit, the utility schedules a disconnect, the electrical work happens (typically one to two days for the physical installation), the inspector reviews the completed work, and then the utility schedules reconnection. In markets where utility crews are backlogged, the reconnect can be the longest wait in the process — sometimes a week or more after the electrician has finished.
For a full walkthrough of what happens during any panel upgrade — from permit application to the inspection and reconnect — see our electrical panel upgrade process guide.