What is a load calculation and why does it matter?
A load calculation adds up the electrical demand of a home using standard code methods, including lighting, appliances, air conditioning, EV chargers and other large loads. The result shows whether the service has room, and it decides whether adding a sub panel is safe.
In the West Valley, air conditioning is usually the largest single load, often with a second system or a heat pump. Pools, hot tubs and EV chargers add more, so a home that seemed fine when it was built can be near its limit now.
A sub panel does not create capacity. It only moves breakers to a convenient place. If the main service is already busy, a sub panel just hides the problem until something trips.
Electricians often estimate demand using the largest loads first. Central air conditioning, an electric range, a dryer, a water heater and any EV charger count heavily, while lighting and small outlets add smaller portions. Your electrician applies the code method to turn that into a number for your home.
Why would you add a sub panel?
A sub panel brings circuits closer to where they are needed, such as a detached garage, workshop, casita, addition or pool equipment area. It saves running many separate wires from the main panel and gives that area its own disconnect and breaker space.
Sub panels are also useful when the main panel is full. Instead of replacing the whole panel, an electrician may add a sub panel with a feeder breaker, as long as the load math works.
Be wary of a sub panel as a patch for a main panel that is old, crowded or showing signs of heat. Those conditions are better solved by upgrading.
Common examples in the West Valley include a detached garage with a workshop, a casita for family, or an outdoor kitchen. In each case the sub panel supplies local breakers, and a dedicated feeder from the main panel carries that area's power back to the source.
What does installing a sub panel involve?
Installing a sub panel involves sizing the feeder wire and breaker, keeping neutral and ground separate in the sub panel, grounding it properly, labeling circuits, and getting the work permitted and inspected. These are code requirements and not a DIY project.
Mixing neutrals and grounds in a sub panel is a classic mistake that can send current onto metal parts. The details differ between an attached and a detached building, which is why a licensed electrician should plan it.
Permits are required for panel changes. In Sun City and Sun City West, which are unincorporated Maricopa County, permits typically go through the county rather than a city.
A detached structure typically needs its own grounding electrode as well, and the feeder size depends on how much load you expect. Work is inspected before walls are closed up, and an inspector checks labeling, bonding and breaker sizing. Skipping that step creates risk and trouble when you sell.
When is a panel upgrade better than adding sub panels?
A panel upgrade is usually better when the main panel is old, crowded, hot, rusted, or too small for new loads like an EV charger, a second AC or a pool. Adding sub panels on top of a stressed main panel only shifts the problem.
If breakers trip often, lights dim when the AC starts, or the panel feels warm, stop and call. Those are signs of an overloaded or failing panel, and they do not wait for convenient timing.
Vortech handles panel upgrades and load planning in Glendale, Peoria, Sun City, Sun City West and Surprise. Use the call button on this page to talk through your situation.
An upgrade may also be the right time to add whole house surge protection, since monsoon storms can send spikes through the service. Bundling that work with a panel change saves a second trip and ensures the new panel is protected from the start.
More questions: Electrical Panel Upgrades: 12 Most Asked Questions Answered