Most commercial build-outs in Lisle don’t start with anyone thinking about the electrical panel. You sign the lease, you plan the layout, you pick finishes, and somewhere down the line an electrician looks at the existing panel and says the space can’t actually power what you are building. Now you have a budget problem you didn’t see coming, and depending on the timing, a schedule problem too.
I want to take the surprise out of that. A panel upgrade isn’t always necessary for a build-out, but there are specific situations where it is, and you can usually see them coming if you know what to look for. Here is when a retail or office build-out in Lisle forces a panel upgrade, why it happens, and roughly what it costs, from the perspective of a licensed electrician who does this work in DuPage County.
What a commercial panel upgrade actually means
When people say “panel upgrade,” they sometimes mean swapping an old panel for a new one of the same size, and sometimes they mean increasing the building’s electrical capacity, which is a bigger job. For a build-out, it is usually the second kind. You are not just replacing hardware. You are increasing how much power the space can safely draw, which can mean a larger panel, new feeders, and in the heaviest cases coordination with the utility to upsize the service.
Most commercial spaces run on at least a 200-amp service. Plenty of build-outs push past what a 200-amp panel can handle and need 400 amps or more, depending entirely on what you are putting in the space.
When a build-out forces the upgrade
The deciding factor is load: how much power your equipment, lighting, and systems will actually pull. A few situations reliably tip a space over what its existing panel can handle.
You’re adding heavy equipment
This is the big one. A standard office with desks, computers, and LED lighting is a light electrical load, and an existing 200-amp panel often handles it fine. But the moment you add equipment that draws hard, the math changes. A restaurant kitchen with commercial cooking and refrigeration, a medical or spa space with lasers or imaging equipment, a salon with multiple stations, a shop with motors or compressors, all of these can push a space to 400 amps or beyond. Refrigeration is especially demanding because it runs continuously, which the code treats more strictly than equipment that cycles on and off.
You’re changing how the space is used
Commercial spaces get re-tenanted for completely different uses all the time. A unit that was a quiet retail shop becomes a restaurant. An office becomes a fitness studio. The panel that was sized for the old use was never meant to carry the new one. When the use changes, the load assumptions change with it, and the existing service often can’t keep up.
You’re subdividing or adding tenants
If your build-out splits a space into multiple units, or adds metering for separate tenants, you are usually adding panels and distribution, and the main service has to be big enough to feed all of it. This is where a building that seemed fine suddenly comes up short.
The existing panel is simply old or maxed out
Sometimes the build-out just exposes a problem that was already there. An older Lisle commercial building near the downtown area may have a panel that is already near its limit, has no spare breaker slots, or is an outdated type that no longer meets code. Adding any meaningful load is the thing that finally forces the replacement.
The load calculation is the whole answer
Here is the part that separates a guess from a real answer. Whether you need an upgrade comes down to a load calculation, and there is an actual method for it. The National Electrical Code, in Article 220, lays out how to add up every load in the space, apply demand factors, and arrive at the amperage the service has to support. You can read more about the code itself on the NFPA’s overview of the National Electrical Code, which is the standard Lisle and DuPage County build on.
A few numbers give you the shape of it. Code requires sizing continuous loads, anything running three hours or more, at 125% of their actual draw, which is why heavy lighting and refrigeration eat capacity faster than people expect. Commercial lighting alone runs roughly 1.3 to 2 watts per square foot for an office and up to about 3 for a restaurant. And there is the 80% rule: a panel is considered tight once its calculated continuous load passes 80% of its rating, so a 200-amp panel gets crowded well before it hits a literal 200 amps. We run this calculation before quoting any upgrade, because oversizing wastes your money on switchgear you don’t need and undersizing sends you back with a failed inspection.
The single most useful thing you can do
Have the load calculation done before you sign the lease, not after. This is the one I wish more tenants heard early. The cost of upgrading a commercial service, new feeders, a larger panel, possibly a new transformer set by the utility, is real money, and it can change whether a given space even makes sense for your business. If you find out about it during construction, you are absorbing a cost you had no chance to negotiate. If you find out during the lease evaluation, you can factor it into the deal, ask the landlord to contribute, or pick a different space. The calculation costs you almost nothing compared to what it can save you.
Roughly what it costs
I won’t pretend there is one number, because the range is genuinely wide. A straightforward panel replacement is the low end. Increasing the service to 400 amps with new feeders is more. And if the utility has to set a new transformer or run new primary conductors to your building, that is where it climbs, sometimes by a lot, and it can add weeks to your timeline because you are now on the utility’s schedule, not yours. The two things that move your number most are how big a service jump you need and whether the utility has to get involved. A load calculation tells you both before you commit.
Getting it right for your Lisle build-out
A panel upgrade done as part of a build-out should be planned, not discovered. When it is planned, it gets priced into the project, scheduled around the rest of the trades, and built to pass inspection the first time. When it is discovered halfway through construction, it becomes the thing that blows the budget and stalls the schedule.
We handle commercial panel and service upgrades across Lisle as part of build-out and tenant-improvement work, starting with the load calculation so you know the real scope before anyone commits. If you want background on how panel sizing works, our guide on what size electrical panel you need walks through the basics, and our piece on how to tell if a panel is outdated covers the warning signs. When a build-out needs separate distribution, our explainer on subpanels is a useful primer.
If you are planning a retail or office build-out in Lisle and want to know whether the space can power what you have in mind, the full picture of what we do for local businesses is on our commercial electricians in Lisle page. Reach out or call (630) 427-5923 and we will run the numbers before you sign anything.
Written by Alexandr Godonoaga, Owner and licensed electrical contractor at Cob Services LLC (Illinois License #26-00032356), serving commercial clients across Lisle, Naperville, Downers Grove, and DuPage County.