400 Amp Service Upgrade

A 400 amp service upgrade is the right answer for a specific kind of building: a large single family home with multiple air conditioning systems and heavy accessory loads, a property with a guest house or workshop on the same meter, or a light commercial space where the connected equipment simply exceeds what a 200 amp service can carry. It is also, honestly, one of the most oversold jobs in the trade.

We install 400 amp services across Broward County and the coastal cities we cover in Miami-Dade and Palm Beach County, and the first thing we do on every one of them is run the numbers to find out whether the building actually needs it. Sometimes the answer is yes and the job is straightforward. Sometimes the answer is that a correctly designed 200 amp service with managed loads does everything the owner wants for a fraction of the disruption. You deserve to know which one you have before anybody orders equipment.

When 400 amps is genuinely the correct size

The load calculation decides this, not the square footage and not the number of bedrooms. That said, certain patterns show up over and over in the homes that legitimately calculate out past a 200 amp service:

• Three or more air conditioning systems. A large two story house on the Intracoastal with separate systems for the main floor, the upper floor, and a garage apartment carries a compressor and air handler load that dominates the calculation. Add electric strip heat in each air handler and the number climbs fast.
• An electric pool heater plus full pool equipment. A resistance pool heater or a large heat pump, a variable speed pump, a booster pump, a salt system, and landscape and pool lighting on a big property adds up to a meaningful block of load on its own.
• Two EV charging circuits. A household with two electric vehicles and two 48 amp chargers is carrying 120 amps of continuous load before anything else in the house turns on.
• An accessory structure. Guest houses, detached workshops, boat lifts, dock equipment, and outbuildings all feed from the main service and need their own feeder, their own panel, and their own grounding arrangement.
• Whole house standby generation. When the intent is to back up the entire property rather than selected circuits, the transfer equipment has to be sized to the service, which drives its own set of decisions.
• Light commercial with real equipment. Restaurant kitchens with electric ranges, fryers and rooftop units, small manufacturing with compressors, refrigerated warehouse space, and multi-tenant suites where each tenant needs their own metered service.

What all of these have in common is calculated demand, not wishful thinking. Before we quote a 400 amp upgrade we produce a written load calculation. For a dwelling, that is a formal calculation using the accepted methods for residences. For a commercial building, it is a different calculation entirely, with continuous loads carried at 125 percent, kitchen equipment demand factors where they apply, and motor loads handled under the rules for motors.

Where 400 amps gets oversold

Here is the pitch we hear about from homeowners: they call about adding an EV charger, and the quote comes back as a 400 amp service upgrade. Occasionally that is correct. Frequently it is not.

A few things that solve the problem without doubling the service:

• Load management on the charger. Modern EV charging equipment can be set to a lower continuous current, or paired with a load management device that monitors the service and reduces charging current when the house is drawing heavily. Since the car sits in the driveway all night, a slightly slower charge costs the owner nothing in practical terms.
• Correct load calculation instead of a rule of thumb. Contractors who add up every nameplate in the house without applying demand factors will always conclude that you need a bigger service. That is not how the calculation works.
• Right-sizing the heating source. An electric tankless water heater or resistance pool heat is often what pushed the house over the line. A heat pump water heater or a pool heat pump can drop the calculated demand dramatically.
• Fixing the panel, not the service. Sometimes the actual complaint is "no room for more breakers," and the fix is a properly sized subpanel or a panel replacement, not a new service.

Going to 400 amps is not a small step up from 200. It doubles the conductor material, usually means larger raceway, brings in different metering equipment, may trigger utility side work including a transformer change, and often requires engineered drawings for the permit. When the calculation supports it, it is money well spent. When it does not, it is money spent on capacity that will never be used.

Metering equipment: what a 320 class socket is

Residential 400 amp services in this market are almost always built around what the utility calls a 320 amp meter socket, sometimes labeled 320/400 class. The rating reflects how the equipment is actually used: 320 amps continuous, with the 400 amp figure describing its short duration capability. When a utility or an electrician says "400 amp residential service," this is the hardware they mean.

These sockets are physically larger than a standard 200 amp can, they use heavier jaws and lugs, and they are frequently supplied as combination units with two 200 amp main breakers built into the same listed enclosure. That combination unit is the workhorse of the residential 400 amp service in South Florida, because it puts the metering, the service disconnect, and the overcurrent protection in one weather-rated enclosure on the exterior wall.

Above this size, self-contained metering ends. Larger services move to current transformer metering, which means a CT cabinet, a separate meter enclosure, and a different set of utility requirements. That transition point matters for commercial projects, because it changes both the equipment list and the utility review timeline. If you are looking at a building whose demand is genuinely past what a self-contained meter handles, the conversation shifts toward three phase service and the equipment that goes with it.

Two 200 amp panels or one 400 amp panel

Both arrangements exist and both are legitimate. The choice depends on the building, not on preference.

Dual 200 amp panels

The common residential approach uses a 320 class meter with two 200 amp disconnects, each feeding its own panel. One panel might serve the main house and the other might serve the pool equipment, the garage, the EV chargers, and the guest house. The advantages are practical: 200 amp panels and breakers are stocked everywhere, the feeders are a manageable size, and you can put each panel physically close to the loads it serves, which cuts voltage drop on long runs across a large property.

The other advantage is that a fault or a service call on one half of the property does not require shutting down the other half. On a big house with a home office or a medical need, that matters.

A single 400 amp panel

A single 400 amp main breaker panel puts every circuit in one place, which is simpler to understand and simpler to label. The tradeoffs are real: the panel and its main breaker are specialty equipment, the feeder conductors between the meter and the panel are large and expensive, and a single point of shutdown means the entire building goes dark for any work at the panel.

How many service disconnects are permitted and how they must be enclosed has tightened in recent code cycles, so the specific arrangement we build depends on current requirements and on what the inspector in that jurisdiction accepts. We design the disconnect arrangement around the code in force at the time of permit, using listed combination equipment or properly grouped disconnects.

Feeders, conduit, and the part nobody photographs

Conductor sizing is where a 400 amp job gets expensive and where mistakes get made. A few realities:

Single family dwelling services get an allowance that lets the service and main feeder conductors be sized below the full service rating, because a house never draws its calculated maximum for long. That allowance is why a residential 400 amp service can be built with conductors that would be undersized for a commercial 400 amp service. Commercial services do not get that allowance. A contractor who applies the dwelling rule to a retail suite or a restaurant has undersized the service, and that failure shows up as heat at the lugs, not as an immediate outage.

Beyond a certain size, single conductors become impractical to bend and terminate, so we run parallel sets. Parallel conductors have their own requirements: each set has to be the same length, the same material, the same size, and terminated the same way, or the current does not divide evenly between them.

The raceway grows with the conductors. A 400 amp underground lateral or a meter-to-panel run typically lands in three inch or larger conduit, with sweeps of adequate radius so the pull does not damage insulation. On a long run across a property we check voltage drop and upsize when the numbers call for it, because a large house with the panel a hundred feet from the meter has a real voltage drop problem if it is ignored.

Aluminum conductors are standard at this size and are entirely appropriate when they are terminated correctly: dual rated lugs, conductors cleaned, antioxidant compound applied where the listing calls for it, and every termination torqued to the value printed on the equipment. Torque is not a formality on 400 amp lugs. A loose lug on a service conductor is a fire, and it is the single most common defect we find on service equipment installed by people in a hurry.

Overhead or underground

Most 400 amp residential services we build here come in underground, and there are good reasons for that.

An overhead drop at this capacity is heavy. The conductors are large, the mechanical load on the mast is significant, and the mast has to be braced to handle it through storm season. Utilities in this region often prefer or require an underground lateral at 400 amps, particularly on newer streets and in neighborhoods where the distribution is already underground.

An underground service brings its own scope. There is trenching across a yard that probably has irrigation, landscape lighting, and a sprinkler main in it. There is conduit at the required burial depth, with warning tape above it in most jurisdictions. There is a transition from the utility transformer or handhole to your meter location, and the utility has rules about who supplies the conductors, who pulls them, and who owns each section. On a waterfront property with a seawall, a pool deck, and mature landscaping, the trench route is frequently the hardest part of the design.

Overhead remains the practical choice on some properties, especially where the existing drop and pole location work and the alternative is trenching under a driveway and a pool deck. When we go overhead at this size, the mast, the attachment point, and the clearances get engineered rather than eyeballed.

Utility coordination and lead time

A 200 amp swap is routine for the power company. A 400 amp service is a service change that gets reviewed. Expect the following:

• An application with the calculated load, not a guess. The utility wants to know the demand you are asking their equipment to carry.
• Engineering review of the supply. The transformer serving your street may not have the capacity for a new 400 amp customer, and the answer can be a larger transformer, a new pad mount unit, or a different point of connection. That work is on their schedule, not ours.
• Approval of the meter location and equipment. Height, clearance, working space in front of the equipment, and unobstructed access for the meter reader all get checked.
• Easement or right of way issues where a new pad mount transformer or lateral crosses property lines.

This is why we start the utility conversation early and why we do not quote a completion date on a 400 amp upgrade until the utility has weighed in. It is the single largest source of schedule uncertainty on the job, and we would rather be straight with you about it than promise a date we do not control. Call (954) 602-0050 and we can tell you what the review has looked like recently in your specific area.

Permits, drawings, and the hurricane zone

Every 400 amp service upgrade is permitted work, and at this size the permit package is more substantial than a residential panel change.

Expect to provide a load calculation, a riser diagram showing the service from the point of connection through the metering to the disconnects and panels, and a site plan when the service is underground. Commercial projects generally require drawings prepared and sealed by a design professional, along with panel schedules and a fault current and short circuit consideration for the equipment being installed.

Broward and Miami-Dade sit in the High Velocity Hurricane Zone, and that affects exterior electrical equipment more than people expect. Enclosures mounted on exterior walls need appropriate product approval, the anchors and fasteners into concrete block have to be specified rather than improvised, and equipment openings have to be sealed against wind driven rain. Generator pads, transformer pads, and exterior disconnects all get scrutinized on this point. An inspector in Hollywood, Fort Lauderdale, or Aventura will look at how the equipment is attached to the wall, not just at what is inside it.

Inspections typically include an underground inspection before the trench is covered, a rough inspection where applicable, and a final. The building department release is what lets the utility set the meter and energize the service.

Designing around EV charging, pool loads, and a generator together

The three loads that most often push a property to 400 amps also interact with each other, and how we arrange them determines whether the system is pleasant to live with.

EV charging. Two chargers on one property can share a circuit with power sharing equipment, or run as separate circuits. On a 400 amp service with dual panels, putting both chargers on the panel that also serves the garage and workshop keeps the heavy continuous loads together and keeps the house panel clean. Our page on EV charging station installation covers the equipment side, and the Level 2 charger installation guide covers what the circuit itself involves.

Pool and spa equipment. Pool equipment on a big property is usually best served by a dedicated subpanel at the equipment pad, fed from the appropriate service panel. That shortens the branch circuits, simplifies the equipotential bonding grid around the pool, and gives a service technician a place to shut things down without walking into the house.

Standby generation. This is where 400 amp services get interesting. Backing up an entire 400 amp service means a service rated transfer switch sized for the whole service and a generator large enough to start the air conditioning compressors, which on a house with three systems is a substantial machine. The alternative that most owners end up preferring is a managed approach: a generator sized realistically, a transfer switch feeding a dedicated panel, and load shedding that lets one or two air conditioning systems run instead of all of them. We work through that tradeoff during generator installation planning, because the decision affects the service design and it is far cheaper to decide before the meter goes on the wall than after.

Light commercial and multi-tenant considerations

For a commercial building, a 400 amp service raises questions a house never does.

The first is voltage. A 240/120 volt single phase 400 amp service and a 208Y/120 volt three phase service carry very different amounts of power at the same amperage, and most commercial equipment, particularly rooftop units, compressors, and commercial kitchen gear, is happier on three phase. If the utility has three phase available at the street, the right conversation is often about voltage rather than amperage. Our commercial electrical services cover that evaluation.

The second is metering and distribution. Multi-tenant buildings need a meter stack or a main distribution section with individual tenant meters, house panels for common area loads, and a clear separation between what the landlord maintains and what each tenant maintains.

The third is continuity. A working restaurant or medical suite cannot lose power for a full day without planning. We schedule commercial cutovers around the business, which sometimes means overnight or weekend work and sometimes means temporary power to keep refrigeration alive during the changeover. When the existing distribution equipment is also being replaced, our commercial panel upgrade work runs alongside the service change so the building only takes one outage instead of two.

What we need from you to quote it

To put a real number on a 400 amp service upgrade, we need to see the property and we need information you may have to gather:

• Photos of the existing meter, main disconnect, and every panel and subpanel on the property, including detached structures.
• Whether the incoming service is overhead or underground today, and where the utility transformer or pole is.
• A complete list of the loads, existing and planned: air conditioning tonnage and quantity, water heating type, pool equipment, cooking equipment, EV chargers, shop tools, elevator, boat lift.
• The conditioned square footage of the house, and of any accessory structure.
• Where you want the new equipment, and any HOA or architectural restrictions on exterior walls.
• For commercial, the tenant list, the equipment schedule, and any planned build out.

The scope moves on a handful of variables: trench length and what the trench has to cross, whether the utility needs to change a transformer, the distance from the meter to each panel, the number of panels, whether existing branch circuits need repair once they are exposed, and stucco or hardscape restoration. We list those out so you can see where the money goes rather than getting one number with no explanation. Homeowners planning a larger project can start on our residential electrical services page to see how the pieces fit together.

Talk to us before you order equipment

The worst time to discover that a 400 amp service was not the right design is after the trench is dug. The best time to have this conversation is while the architect is still drawing, while the pool contractor is still specifying the heater, or before you have committed to a generator model.

Bring us the plans and the load list, and we will produce the calculation and tell you plainly whether the building needs 400 amps, needs a well designed 200 amp service, or needs a three phase service instead. Reach us at (954) 602-0050, and we will start with the math.