Will My Service Take It?
Before you buy an EV charger, a heat pump or a hot tub, it is worth knowing whether the house can already carry it. Answer what is here and what you are adding, and this gives you a straight answer.
How This Calculation Works
Where the Numbers Come From
This follows the standard method in Article 220 of the National Electrical Code, which is the calculation an electrician runs before quoting a service upgrade. General lighting is counted at three volt-amps per square foot, two small appliance circuits and a laundry circuit are added at 1500 volt-amps each, and a demand factor is applied to the total because a house never runs everything at once.
Fixed appliances are added at their nameplate rating, with a discount where there are four or more of them. Heating and cooling are counted once, at whichever is larger, because they do not run together. An EV charger is counted at 125 percent of its rating, because it is a continuous load.
Why It Says Borderline Rather Than Fine
Because the honest answer near the limit is that it depends on things a form cannot see. Whether the panel has physical spaces left. Whether the busbar is rated for what you want to put on it. What condition the equipment is in, and what else you are likely to add in the next few years. Anything above about eighty percent of the service is reported as borderline rather than as a pass.
A number close to the limit is not a refusal. It usually means there is a choice to make: upgrade the service, fit load management, or size the new equipment down.
Load Calculator Questions, Answered
How Accurate Is This?
It follows the standard method in Article 220 of the National Electrical Code, which is the same calculation an electrician runs. What it cannot do is see your panel, read the nameplate on your actual equipment, or account for anything unusual in the house. Treat it as a good indication of whether you are comfortable, borderline or short, not as the number that goes on a permit.
What Is the Difference Between This and What an Electrician Does?
Mostly the inputs. We do the same arithmetic on the real nameplate ratings, with eyes on the panel and the service entrance, and we check the things a form cannot ask about: whether the panel has physical space, whether the busbar is rated for it, and what condition the equipment is in.
It Says I Am Short. What Are My Options?
Usually one of three. Upgrade the service, which is worth doing anyway if the panel is also full or obsolete. Fit load management, which is common for EV chargers and throttles the car when the rest of the house is busy. Or pick lower-rated equipment. Which is right depends on what else you are likely to add in the next few years.
Does a Bigger Service Cost More to Run?
No. The service size is the capacity available to you, not the amount you use. A 200 amp service does not draw more than a 100 amp service; it just does not run out.