AC and DC MCBs

[goldyvb]

Hi all,

I am just curious of the effects of using AC MCB circuit breakers for DC applications (i.e. using a 4 Amp C-Curve AC MCB to protect a 24VDC control circuit). I am aware of the arc extinguishing problems at the high end of the scale but am curious (mainly because of the price difference) for this type of application.

Thanks

 

[dpc]

Your circuit breaker must be tested and listed for dc operation. The dc current ratings will be much lower than for ac. But if it not listed for use on dc systems, I would not assume it would work at all.

 

[goldyvb]

Thanks for that DPC. As a little experiment, and to settle my curiosity, I decided to put some AC breakers to the test. I put a 4A AC MCB breaker in series with a multimeter in my battery circuit in my car (12VDC). As it turned out, the breaker does operate, and the times correspond to the standard C-curve for the associated current. I tried currents below, equal to and above the rated current (through combinations of indicators, lights and high beams). Each time, the breaker tripped or didn't trip as expected. The same experiment was repeated with the 2A AC breaker with similar results. So as I see it, the breakers work on 12VDC as expected, although I would still not be sure about their operation for different load sizes and voltages, and any further feedback would be appreciated.....

 

[waross]

Hi dpc;

The dc current ratings will be much lower than for ac.

Did you mean to say "The dc VOLTAGE ratings will be much lower than for ac.
I think the current ratings are the same, but the voltage ratings are much lower.
respectfully

 

[dpc]

I was trying to say that the interrupting rating for dc will be lower than for ac. Continuous current (rms) would be the same.

Although in looking through an old GE publication, I find that although the dc interrupting levels are lower than for ac, the levels are not as much lower as I remembered. It varies quite a bit depending on the breaker and if it is one pole or two pole.