DC voltage rating on molded case breaker

[PhaseShift]

I was looking a a 480V molded case breaker and noticed that it had a 250V maximum rating for DC voltage. Why does a breaker have a lower voltage rating for DC voltage as opposed to AC?

 

[Jraef]

I was looking a a 480V molded case breaker and noticed that it had a 250V maximum rating for DC voltage. Why does a breaker have a lower voltage rating for DC voltage as opposed to AC?

It takes more separation to interrupt a DC arc as the contacts open and that problem increases with voltage, so generally a DC voltage rating on a breaker will be lower than the AC rating. But there are some breakers that have been tested and listed by UL for higher DC voltages by using series connections of the 3 or 4 pole breakers.

 

[Besoeker]

I was looking a a 480V molded case breaker and noticed that it had a 250V maximum rating for DC voltage. Why does a breaker have a lower voltage rating for DC voltage as opposed to AC?

AC has natural zeros so it is easier to break the current than with DC which does not.
Thus, as Jraef say, you need greater contact separation.

 

[LarryFine]

Thus, as Jraef say, you need greater contact separation.

It takes more separation to interrupt a DC arc as the contacts open and that problem increases with voltage, so generally a DC voltage rating on a breaker will be lower than the AC rating. But there are some breakers that have been tested and listed by UL for higher DC voltages by using series connections of the 3 or 4 pole breakers.

Actually, it's faster contact separation, which is effectively the effect (sorry) of placing several contact sets in series.