Electrical Basics: Part 3

Apr 23, 2024

After exploring electrical concepts in Part 1 and Part 2, this section provides a breakdown of a critical component to charging electric vehicles - circuit breakers.

A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by overcurrent conditions. It works by interrupting the electric current when it exceeds its design limitations, cutting off the supply of energy and preventing damage to the circuit. As a common example of use, when electricity enters a home, it goes to a distribution panel, where it’s divided into a number of circuits. Each circuit is protected by a breaker. The circuit breaker senses the excess current and “trips” to stop the flow of power before damage occurs.



Circuit breakers are classified based on their voltage rating and amperage rating. The voltage rating of a circuit breaker is the maximum voltage that the breaker can safely interrupt. The amperage rating of a circuit breaker is the maximum current that the breaker can safely carry continuously.

An ampere (amp) is the unit of measurement for electric current. It is defined as the amount of electric charge that flows past a point in an electric circuit per unit of time. 

In the context of circuit breakers, the amperage rating is the maximum current that the breaker can safely carry continuously without tripping. Circuit breakers are designed to trip when the current flowing through them exceeds their amperage rating, thereby protecting the electrical system from damage caused by overcurrent.


Typical applications will have both a main circuit breaker (the largest breaker in the electrical panel that controls the power supply to the entire application) and branch circuit breakers ( smaller breaker that control power to a specific area or device in the application). If there is a short circuit or an overload in a branch circuit, the branch breaker will trip and cut off the power to that circuit. If there is a problem with the main service wires or the electrical panel, the main breaker will trip and cut off the power to the entire system.



The National Electrical Code (NEC) by the National Fire Protection Association (NFPA) 80% rule is a guideline that recommends that circuit breakers should not be loaded to more than 80% of their rated capacity for continuous loads. This is because circuit breakers can overheat and fail if they are loaded to their full capacity for extended periods of time.

For example, if a circuit breaker is rated for 100 amps, it should not be loaded with more than 80 amps of continuous load. This is because the circuit breaker may overheat and fail if it is loaded to its full capacity for extended periods of time. The 80% rule is designed to ensure that circuit breakers operate safely and reliably, and it is an important consideration when designing electrical systems.



Circuit breakers are an essential component of the electrical infrastructure for fast charging stations. They are needed to protect the charging station and the EV from damage caused by overcurrent or short circuits.

In the context of fast charging, circuit breakers are typically part of the switchgear and located in the power distribution panel. The power distribution panel is responsible for protecting and distributing the electrical power from the main power source to the charging station’s components.

EV chargers are considered as continuous loads per the NEC (2023), thus circuit breaker protection for EV charging sites must meet the 80% rule.

What's Next?

Part 4 will introduce EV Charging Basics like how EV charging works, levels of chargers, and types of connectors.




The NexPhase™ Smart EV Switchgear is an all-in-one panel containing the entire infrastructure required between the utility service and up to four Level 3 DC fast chargers totaling 800 kW. Unlike any switchgear of its kind, the NexPhase™ features cutting-edge grid intelligence for complete EV charging station remote uptime monitoring and control.


Provides ongoing EV charger state-of-charge and utility power monitoring, enabling CPOs to accurately pinpoint charger outages, even when charger communications are down. The remote power cycle capability helps bring chargers back online faster.


The embedded monitoring system provides remote access to real-time switchgear, utility power, and charger health data with automated alarms for condition-based maintenance planning.


Eliminates the lengthy design process of traditional post-and-frame systems, which require additional costs to design, permit, and source a mixed-manufacturer panel system. NexPhase™ eliminates sourcing and supply chain delays as a single-manufacturer, turnkey solution.


Requires minimal on-site connections for the incoming power and outgoing charger connections, drastically reducing on-site installation time and electrician costs.




The Fundamentals of EV Charging

May 15, 2024 - Charging an electric vehicle (EV) is a complex interaction involving sophisticated site infrastructure and advanced vehicle systems. This process requires a seamless communication exchange between t...

Electrical Basics: Part 3

Apr 23, 2024 - A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by overcurrent conditions.

Electrical Basics: Part 2

Apr 09, 2024 - To charge their batteries, EVs need to connect to a power source that can deliver a certain amount of energy over a certain period of time. But what is the difference between power and energy, and w...
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