AC Circuit Breaker
In North America, the grid alternates at 60 Hz or 60 cycles per second; hence the name “Alternating Current”. The voltage alternates between +V and –V, 60 times a second.
That means there is a point at which the voltage is 0v, 120 times per second, zero every half cycle. It is at this 0v point that the AC breaker will “break” the connection, extinguish the arc, and protect the wiring from too much current.
DC Circuit Breaker
In contrast, a DC circuit does NOT alternate. It stays at a constant voltage. Since there is no 0v point, the AC breaker design will NOT work in a DC circuit.
The DC Circuit breaker uses a magnet to attract the arc, pulling it from the air gap, and extinguishes it. The AC breaker is NOT equipped with a magnet, and cannot extinguish a DC arc.
By and large, DC application is much more rigorous than AC. The main reason, in the case of AC, is zero crosses over at the end of each half-cycle. This helps in the cessation of current automatically.
AC device in DC applications, require the derating of both voltage and current. The extent of derating is normally furnished by the manufacturer. Another factor to be considered is the inductance in the load to be disconnected.
Normally expressed as PF in AC and time constant in case of DC loads. More the dominance of inductance, arc quenching becomes more rigorous. A DC device is always more elaborate and bulky. Clearing the arc in an AC application for a DC device may not be a limitation.
But the suitability of the coil and associated other safety devices are to be ascertained.
The short circuit and overload mechanism for the DC and AC Circuit breakers are the same because RMS AC is equivalent to DC. Circuit breakers are manufactured on the basis of the current so if the current rating of AC circuit equals the current rating of DC then it can be utilized.
The other compatibility of these circuit breakers is the power handling capacity that is also equally significant.
But there is a difference is ‘arc quenching’ methods.
AC current crosses zero in a cycle so AC arc is easier to quench than DC. This makes DC breakers different than AC.
Why arc quenching?
In the case of a short circuit, when contacts separate physically, the current can still flow through arc or plasma that forms in between the contacts. This lengthens the current breaking period. Short circuit current must be interrupted as early as possible so as to prevent further damage.
As for the DC circuit breaker, the ones Cohomer sells can be used DC current and are rated for 400 or 600 volts far more than what most people ever need for solar. using automotive fuses breaker in most 12v and 24v solar circuits system.