Circuit breaker sizing for DC loads
Circuit breaker sizing for DC loads
(OP)
How do you properly size a circuit breaker to operate at 24VDC? We are now using 24VDC control circuit voltages and I want to be sure circuit protection is correct.
Thanks
Thanks





RE: Circuit breaker sizing for DC loads
You'll find more than enough information and vendors of such equipment in the search results.
RE: Circuit breaker sizing for DC loads
Sorry I should have mentioned this is an Industrial Application. My concern goes more to properly rating an AC breaker for DC use, assuming my supplier does not make an industrial DC breaker. As an example the system I am currently following up is using standard industrial DIN rail mounted breakers rated at 277V 6A, which if we don't think about AC for a moment, is about 1662 watts. The relay contacts that are being protected by the CB are rated at 24VDC @ 6A or 144 watts. The question I have posed to the vendor is do we need to derate the CB, my gut says yes, thus I would need about a .5A 277 volt relay. I need some other opinions to get a warm fuzzy feeling.
RE: Circuit breaker sizing for DC loads
RE: Circuit breaker sizing for DC loads
Not expert here and always wanting to learn.
Why you are considering the circuit breaker as protection for the relay? I have always considered the circuit breaker as protection against overheating due to overcurrent and have always considered this to involve mainly the wire. Circuit breakers can do this job very well but I have always thought that relay protection is not predictable, which is why UL requires actual testing for group use listing (breakers and contactors).
ant to consider breakers designed for the aerospace industry. Many are DC rated.
PUMPDESIGNER
RE: Circuit breaker sizing for DC loads
Many AC breakers are listed for DC use (of course different current /voltage than AC). As TWW indicated search and ask Square D, GE, Cutler Hammer etc.
RE: Circuit breaker sizing for DC loads
The manufactures provide more information. There are four pole circuit breakers that have recommended two and two contact connections in series to be used for DC applications.
RE: Circuit breaker sizing for DC loads
PUMPDESIGNER
I am protecting relay contacts rated at 6A, so the relay contacts end up being the 'weak link' in terms of current capacity. In the past when using a typical control relay the rating was 10 A. We are now using Safety Relays which have an 8A fast blow rating and a 6A slow blow rating and we are now using 24VDC for our control voltage.
RE: Circuit breaker sizing for DC loads
http://www.ferret.com.au/articles/2c/0c019b2c.asp
for DC Circuit Breakers, 3 and 6ADC
http://www.ferret.com.au/articles/3b/0c00de3b.asp
for DIN - T series miniature Circuit Breakers