Thinking of using a fast charger for your EV? You might want to check your home’s electrical box before plugging in.

National Grid, a British utility company, has published a think piece about the feasibility and practicality of employing a fast charger at home. In it, the company postulates different scenarios which may scupper the plans of some EV owners … or at least prepare them for some extra infrastructure costs.

Many homes across America, particularly those not using electric baseboard heaters as their main source of heat, tend to have a 100-amp breaker installed as the main fuse. Some older homes may have a main fuse of 60 to 80 amps.

Slow chargers, of the type which take the better part of a day to fully charge an EV battery, are generally rated at 3.5 kilowatts and draw 16 amps. If one were to use a more robust charger, say 11 kilowatts, 48 amps would be required.

Basic math tells us we have a problem. If one’s EV charger is hoovering 48 amps, there will not be enough capacity remaining on the electrical system of older homes to turn on the oven or even plug in a kettle.

An average home with a 100-amp main breaker, on the other hand, can easily bear the load of the 11-kilowatt charger. For perspective, a charger of this rating could fully charge a Tesla Model S with a 90kWh hour battery in about six hours, if the Tesla were 25 percent full when plugged in.

Faster chargers than even this exist of course, and it is at this point that even most modern homes will fail to keep up with the electrical demand. A 22-kilowatt charger would charge the same Tesla given in the example above in about three hours, but pretty much all other electrical equipment in the house would have to be turned off as the charger will help itself to a full 96 amps of juice.

In reality, an 11 kilowatt charger would be the best compromise, offering a decent rate of charge without dominating the electrical load of one’s home. In our “gotta-have-it-now” society, however, it is certain that more and more folks will want to install the largest EV charger available. It behooves them to perform a full assessment of their home’s electrical system to avoid unexpected costs and upgrades.

EV owners, then, suddenly have another variable to consider when considering a home to rent or buy. It is worth noting that some homes, especially those which have electric baseboard heaters as their main source of warmth, may have a robust 200 amp service installed. If that’s the case, one has plenty of breathing room.

National Grid poses these and other interesting scenarios in their think piece, such as the infrastructure required to charge EVs in the same amount of time it takes to fuel up a conventional car. The entire report can be found here.