Glossary

Circuit breaker

Unit A · Also Miniature circuit breaker, MCB

What is Circuit breaker?

A resettable protective switch that protects the cable against overload and short circuit. On board it is common as a switching element in switch panels — protection and operation in one component.

What matters about Circuit breaker in practice?

On the AC side, double-pole versions are used, because otherwise the wrong conductor would be disconnected at a reverse-polarity shore socket. On the DC side the polarity is defined, so single-pole is sufficient there.

The rating depends on the cross-section of the protected cable, not on the load. And like every fuse, it belongs as close as possible to the source.

Which rating is right?

The rating depends on the cable being protected: it must be below the cable’s permissible current rating and above the load’s operating current. For motors and pumps with high starting currents there are versions with a slower tripping characteristic.

May household circuit breakers be used in a DC circuit?

Only if they are expressly approved for direct current and the system voltage. Direct current extinguishes the arc less readily than alternating current when switching off, so the DC breaking capacity must be stated in the data sheet.

Where are circuit breakers installed?

  • In the switch panel, where they also serve as switches for the loads.
  • In the sub-distribution close to the source, so that the whole cable is protected.

The page boat fuses gives an overview of fuses and circuit breakers on board.

Related terms

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