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FAQs

How should I choose a circuit breaker for a high-power DC power supply?

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Product Support FAQ

When using high-power DC or regenerative power supplies, the current rating of the circuit breaker must be greater than the maximum input current of the power supply plus 10%.
For example, the RE650-23 (15 kW, 3-phase 220 V input) of the RE series  of high-power DC power supplies has an input current of up to 68 A (at rated output) and an inrush current of up to 150 A peak. In this case, the breaker's current rating does not need to be higher than 150 A. This is because inrush current, depending on the model, only flows for a few milliseconds when the power is turned on or when the OUTPUT is turned on. The breaker will not react (trip) in this amount of time due to its operating characteristics. There is no problem if you select the rated current of the circuit breaker by adding about 10% of the maximum input current listed on the DC power supply's datasheet.

Circuit breaker | Matsusada Precision
RE series | Matsusada Precision

In the case of RE650-23 (15 kW, 3-phase 220 V input), assuming it is used up to its maximum rated output, it is sufficient to have a circuit breaker with a margin of 68 A input current + 10% or more. In other words, 68A + 10% = 74.8 or more (in this case, a 100A circuit breaker is recommended). In addition, the instruction manual may list the current rating of the Fuse (electrical) or circuit breaker built into the product. For those, please consider the same rated current as that described in the instruction manual.

Please note that if the circuit breaker has high-speed and low-speed operating characteristics, please select the low-speed type. High-speed type may trip due to inrush current.

Note: When using our products via Earth Leakage Circuit Breakers, the breaker may trip due to leakage current from the input filter circuit. (See also: Harmonic Outflow Current Calculation Form)

Circuit Breaker Selection Considerations

Circuit breakers can be classified in various ways based on interrupting type, construction type, voltage class, etc. Circuit breakers for low-voltage applications include the following types:
  • Molded Case Circuit Breaker (MCCB)
  • Motor Protection Circuit Breakers (MPCB)
  • Earth Leakage Circuit Breakers (ELCB)

Connect a common Molded Case Circuit Breaker (MCCB) to the AC power source at the input of the DC power supply

The breakers have characteristics.
  • High-speed type (instantaneous type)
  • Low-speed type

Use a low-speed type breaker connected to the power supply. It is also recommended that the operating range be determined from current and time operating characteristic diagrams.

The physical size and maximum current rating of circuit breakers are expressed in Ampere Frames (AF). Circuit breakers generally come in the following types of ampere frame (AF) and rated current:
  • 30A
  • 50A
  • 60A
  • 100A
  • 125A
  • 150A
  • 250A
  • 400A
  • 600A
  • 800A

*Ampere frame and rated current types vary depending on the manufacturer.

Example of Circuit Breaker Manufacturers.