Panel Upgrades Are Common—And Often Necessary—Before EV Charger Installation

Twenty years of electrical work in Montgomery County has taught me this: Most homeowners are surprised when I explain their electrical panel needs upgrading before Tesla Wall Connector installation. They shouldn’t be—older homes weren’t designed for modern electrical demands. Here’s the reality in Spring, The Woodlands, and Conroe neighborhoods built before 2010: Many homes have 100-amp or 150-amp electrical service. These panels were sized when household electrical demand meant one refrigerator, one window AC unit per bedroom instead of central air conditioning, a gas clothes dryer instead of electric, and no pool pumps, hot tubs, or EV chargers. Now add a Tesla Model 3 drawing 48 amps for overnight charging. The math doesn’t work. I recently completed a load calculation for a 2005-built home in The Woodlands with 150-amp service. The homeowner’s existing electrical demand is calculated to be 142 amps during peak usage—air conditioning, electric range, water heater, pool pump, and landscape lighting. They had 8 amps of available capacity. A Tesla Wall Connector requires 60 amps of breaker capacity for the 48-amp continuous load plus the required 125% safety factor. The solution required upgrading to 200-amp service panel. This meant coordinating with CenterPoint Energy for new utility service, installing a new meter base, replacing the entire service panel, and updating the grounding electrode system to current code. Total project cost: approximately $3,500 before the Tesla charger installation even began. Some homeowners ask whether they can just install a smaller charger that draws less current. Technically, yes—Tesla Wall Connectors are adjustable from 15 to 48 amps. But that defeats the purpose of home charging. Reducing to 20 amps extends your overnight charge time from 8 hours to potentially 16+ hours, meaning you can’t fully charge between evening arrival and morning departure. The International Association of Electrical Inspectors (IAEI) specifically recommends panel capacity evaluation before any Electric Vehicle Supply Equipment (EVSE) installation. This isn’t upselling—it’s preventing a scenario where your main breaker trips repeatedly because your electrical service can’t support your home’s total demand. Panel upgrades also future-proof your home. If you’re adding one EV charger today, you’re likely adding a second when your spouse gets an electric vehicle. You might add solar panels with battery storage. You might convert from a gas water heater to electric heat pump technology. A 200-amp panel accommodates these additions; a 100-amp panel doesn’t. Reference: International Association of Electrical Inspectors (IAEI) EVSE Installation Standards (iaei.org)