How do I choose a circuit breaker with the same frame?

Create Date: 2024-8-30 12:03:23|Source: Fuji Electric/Fujielectric

Following the last release of the circuit breaker Q&A, we have received new circuit breaker inquiries one after another, and this time we have selected the questions about the "protection function" with a high interest rate for answers:

(1) What exactly is a "protection function"?

(2) How should I look at the "action characteristic curve"?

(3) When selecting, how should I choose multiple circuit breakers with the same frame?

(4) What happens if the circuit breaker is turned on a high current?

What exactly is a "protection function"?

Protection function: Protect the equipment with the right combination to avoid the failure of wires and loads when current flows through it.

In the event of an accident in the circuit, the equipment used to shield the accident circuit can be combined, so that the faulty circuit can be shielded before the previous protector is closed, and the power supply to the normal circuit can continue to ensure that the protection characteristics of each appliance do not overlap. (This is called a selective short circuit)

What should you think of the "action characteristic curve"?

We need to observe its "long-delay trip characteristics" and "instantaneous trip characteristics".

When observing the long-delay trip characteristics, pay attention to whether long-term overcurrent protection is appropriate?

When observing the instantaneous trip characteristics, is it appropriate to pay attention to the overcurrent protection for a short period of time?

If you want to merge multiple circuit breakers, you must consider that the action characteristic curves do not overlap.

When selecting a model, how do I choose multiple circuit breakers with the same frame?

Different circuit breakers have different shielding performance and blocking speed. In order to protect the machine, the current and timing of the shielding are optimized. Depending on the load used, the load characteristics (curve of the operating current) also differ.

For example, in the case of a motor load, a circuit breaker with a larger characteristic curve than the motor starting current must be selected to prevent accidental tripping due to the high current flowing during operation.

How do I choose a circuit breaker with the same frame?

What happens when a circuit breaker is turned on a high current?

Above we have mentioned the main points of choosing a circuit breaker.

But what happens if the device doesn't have protection?

Let's take a look at the test footage at the Fuji Electric Proving Ground.

The first is the screen when it is correctly selected.

Conversely, what if the circuit breaker is not selected correctly?

The following is a test video of a circuit breaker with a shielding capacity of 400A and 100A and a current of 10kA.

Note the circuit breaker handle circled in red in the picture below.

When the correct product is selected, the upper circuit breaker can continue to supply power because the overcurrent is cut off before the lower circuit breaker closes.

On the other hand, if the wrong product is selected, it will lead to the failure of the lower circuit breaker to cut off normally, and the failure of the upper circuit breaker to operate normally, and even affect other equipment.

Power stagnation in a normal circuit can expand the area of influence or even cause the device to stop working.

To prevent these accidents, be sure to select a circuit breaker with an operating characteristic curve that is suitable for both "protection function" and "load".

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