NEC 220.87 · 625.42 · 210.23

Can My Panel Handle It?

Adding an EV charger, heat pump, water heater, or induction range comes down to one question: can the service take the load, and if not, what is the workaround? Pick what you are adding and get the exact calculator.

Quick answer: Whether a panel can take a new load is a demand question, not a breaker-count question. NEC 220.87 is the clean path: 125 percent of the highest metered demand over the last year, plus the new load, must stay at or below the service rating. When it comes up short you have three honest moves before a service upgrade: manage demand (an EV management system), reduce the load (a 120V plug-in appliance class), or upgrade. None of them ever let you undersize a branch circuit.

What are you adding?

EV charger

Size the wire, breaker, and panel headroom for a Level 2 charger install, with the GFCI rule and a parts list.

Biggest charger without a panel upgrade

Heat pump or AC condenser

Enter the nameplate MCA and MOCP for the breaker, wire, and ground the condenser needs.

Sizing the heat pump first? Capacity at 5F

Heat pump water heater

The 240V hybrid circuit, or the new 120V plug-in class that can share an existing circuit.

Induction range

The 240V range circuit, or the battery-buffered 120V plug-in class sized from the wall draw not the burner.

Measure the whole panel

The NEC 220.87 existing-load check: one year of metered demand against the service rating, for any new load.

Something else

Look up the running amps for a common appliance, then size its circuit.

The measured-demand path (NEC 220.87)

The most defensible way to prove a panel can take a load is not to add up nameplates, it is to use what the house actually draws. NEC 220.87 lets you take the highest 15-minute demand from twelve months of the utility's metering data, multiply it by 125 percent, and add the new load. If the total stays at or below the service rating, the panel takes it. This is why two identical 100A panels can give different answers: the one already running electric heat and a dryer has less headroom than the one that does not. The load calculator runs both this check and the 220.82 whole-service method, with every step shown.

No panel upgrade? The workarounds

When the calc comes up short, these add the load without new service conductors. Each is honest about why it works, and none of them undersize a branch circuit.

EV energy management (EVEMS)

A load-management device sheds or throttles the charger when the rest of the house is drawing hard, so the SERVICE calc allows a bigger charger. The branch circuit is still sized to the full charger output; only the service-level demand is managed (NEC 625.42, 220.70).

120V plug-in heat pump water heater

The 120V heat-pump-only class draws far less than a 240V hybrid, so it can run on an existing 15 or 20A circuit, shared under NEC 210.23(B)(2). It is a genuinely smaller load, not a shortcut.

120V plug-in induction range

A battery buffers the burners, so the wall draw is 12 to 15A on 120V instead of a 40A/240V range circuit. Sized from the wall current under NEC 210.23(B)(1), not the burner kW.

Frequently Asked Questions

How do I know if my panel can take a new load?

The cleanest path is NEC 220.87: take the highest demand from twelve months of utility metering data, multiply by 125 percent, and check that it plus the new load stays at or below the service rating. It beats guessing from the breaker count because it uses what the house actually draws. The load calculator runs this for you and shows every step.

What if the calculation says the panel is full?

You have three honest options before a service upgrade. Manage demand: an EV energy management system limits the charger when the house is busy, so the service calc allows it while the branch stays sized to the full charger. Reduce the load: the 120V plug-in classes of heat pump water heater and induction range draw far less than their 240V versions. Or upgrade the service. The first two add the load without new service conductors; none of them let you undersize a branch circuit.

Does a load management device let me use smaller wire?

No. This is the one thing techs get wrong. An energy management system relaxes the SERVICE calculation, never the branch circuit. The wire and breaker for the charger are always sized to its full rated output. The device only prevents the total house demand from exceeding the service.

Run the whole job in your AI. Every calculator here also runs inside Claude and ChatGPT through the Intry MCP, and you can keep each reading as one job in the Intry app so the panel, the charger, and the drop all stay together.