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What's The 80% Rule?

The 80% rule is a requirement in the National Electric Code (NEC) mandating that any circuit that is used for a continuous load should be de-rated to 80% of its breaker rating. A charging EV falls into that continuous use category, so you should only charge an EV at 80% of the breaker rating.

In practice, if you use consumer EV charging products, they will obey this rule. So an EVSE that plugs into a normal 15A household circuit will only draw 12A. The biggest receptacle in common use is a 50A NEMA 14-50 or NEMA 6-50, and EVSEs that can plug into those receptacles will limit their charging to 40A.

Incidentally, there is a quirk in the electric code that allows you to install a 50A rated receptacle with only a 40A breaker. That's the reason why the Tesla Mobile Connector, for example, only charges at 32A with a 50A rated adapter plug. Since many consumers won't realize they need to check their breaker for a random 50A receptacle, the Tesla Mobile Connector errs on the side of caution and maxes out at 32A (of course, this makes the product cheaper, lighter and smaller too).



Charging FAQs

How to charge (EVSEs, Receptacles)
Charging from 120V Receptacles
All About EVSEs
DIY EVSE Installation
Charging Standards: J1772/NACS/Tesla???
What's a Magic Dock?
Mobile EVSEs
DC Fast Charging
AC Public Charging
Extension Cords
What's The 80% Rule?


Adapters For Tesla/NACS EVs
Adapters for non-Tesla EVs
Beware Ford Lightning Mobile w/ Adapters
How To Make Your Own Adapters
Never Use RV Adapters


North American Electricity Primer
Receptacle Identification
Overloaded Panel: How To Load Share
Condo Charging Resources
Campground Charging Tips
Vehicle To Load

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