Electrical Basics: Part 3
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.
HOW CIRCUIT BREAKERS ARE RATED
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.
TYPES OF CIRCUIT BREAKERS
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 breakers that control the 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 80% Rule
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.
HOW DOES THIS APPLY TO EV CHARGING?
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.