Why doesn't the breaker trip right away when you go over the rated current?

Owned by Herrick Hu
Last updated: Sept 17, 2022
2 min read

To explain why breaker don't trip right away when you run 30 amps or more through it, you need to understand 2 concepts.

The Breaker:

  1. Breakers in your electric panel are commonly known as thermo-magnetic breakers, aka “air breakers”. Just as the name suggest, there is the “Thermo” component which protects against over-current, where higher current will overheat this component gradually and eventually cause the breaker to Trip. Then there is the “Magnetic” component which protects against short-circuit, where extremely high current caused by the short circuit will create a magnetic fields that trips the breaker in fractions of a second. This youtube video by Wrapped Perception does an excellent job of explaining how it works in slow motion.

The Trip Curve:

  1. Each model and type of circuit breaker has a slightly different Trip Curve. The trip curve tells you how long and at what amperage it will take to trip the breaker. Conditions on the left side of the curve means it will never trip. Conditions on the right side of the curve means it will definitely trip. Values that falls inside the curve means the trip time will vary depending on ambient temperature. This youtube video by Schneider Electric explains it nicely.

Once you understand the Trip Curve, you will realize that when going over the rated currently by few amps will likely never trip the breaker. Even when you are at 1.25x the rated current, it could take over 1 hour to trip, and at 1.5x could take over 10 minutes.

 

Our splitter switch has a breaker that's rated for 25amps, It will trip earlier than your house's breaker which will be likely at 30 amps, thus providing an extra layer of safety.