AC vs DC Breakers

[ChrisUSA]

I am trying to find out a clear difference between AC circuit breakers and DC circuit breakers. I am working with low voltage applications. I have been searching online and some people say they are interchangeable (using 120VAC breakers in a 12VDC application)and some say they aren’t; but nobody gives reasons to back up there statements. If anyone has any theory on this it would be greatly appreciated!! Thanks

 

[davidbeach]

AC goes through a natural current zero every half cycle; DC never does. AC is much easier to interrupt therefore than DC. Every breaker includes listed ratings, if it has a DC rating it has been evaluated for use on DC, if not it hasn't and should not be used for DC. Any breaker with an electronic trip unit will not have a DC rating as the current transformers used won't measure the DC current.

 

[MacRae]

Further explanation concerning AC being easier to interuupt than DC. DC switches and breakers must pull the contacts further apart when breaking the circuit. This is because DC does not pass through zero, full current will be flowing at any instantainious moment. Due to basic inductive principles current at rest tends to stay at rest and the opposite is also true. So, in this case, when the breaker, er, breaks; current will try to keep flowing and arc across the contacts. Subsequently, welding the contacts together eventually, if not immediately. This is why most AC/DC rated devices have a lower voltage rating at DC verses AC.

Ian Rines
Harris Corporation
Palm Bay,FL