×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

AC and DC MCBs

AC and DC MCBs

AC and DC MCBs

(OP)
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

RE: AC and DC MCBs

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.  

RE: AC and DC MCBs

(OP)
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.....

RE: AC and DC MCBs

Hi dpc;

Quote:

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

RE: AC and DC MCBs

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.  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources