AC vs DC Panels and Breakers

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Can standard AC panels and breakers be used in the DC side of the system? Or are there special DC panels and breakers?
Basically is a 20 Amp 120v AC breaker good for 20Amp 12v DC circuit?

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: AC vs DC Panels and Breakers

    The answer is "maybe"... You need to find the DC ratings of the breakers and panel. DC is actually much more difficult to "break" with a switch as it tends to sustain arcing much better than AC.

    So DC switches/breakers are either usually physically larger or have much lower ratings than their AC equivalents.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
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    Re: AC vs DC Panels and Breakers

    The only commonly available AC breakers that I know of that also are DC rated are the Square D QO series and they are only rated for 48 volts. I have used them on the DC side of 24 volt PV systems.
  • marks
    marks Registered Users Posts: 17
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    Re: AC vs DC Panels and Breakers

    In my system the AC and DC breakers are distinctively different, and not interchangeable.
  • System2
    System2 Posts: 6,290 admin
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    Re: AC vs DC Panels and Breakers

    As Mikeo mentioned, the Square D model QO breakers are commonly available 120 Volt AC breakers, which are ALSO rated for use in DC circuits up to a max of 48 volts. Very few if any other AC breakers are rated for DC use. So if you don't use Square D QO breakers, you will end up with different breakers for AC, from what you will use for the DC side of things.
    Cheers
    Wayne
  • System2
    System2 Posts: 6,290 admin
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    Re: AC vs DC Panels and Breakers

    Link to Square D QO breaker info direct from Square D.

    http://www.squared.com/us/misc/faqInternet.nsf/2a7a2a67c5b079a085256a9900703521/d9a8871665a8120685256c1b0062f150?OpenDocument

    Cheers
  • adas
    adas Solar Expert Posts: 136 ✭✭✭✭✭
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    Re: AC vs DC Panels and Breakers

    Aloha, the local PV techie says the DC breakers have a knife inside to help break the more durable arc.
    frank
  • jnh
    jnh Registered Users Posts: 8
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    QOT tandem breakers OK for DC?

    Are the "tandem" QOT breakers (for fitting two single-pole circuits in one panel space) also rated for DC to up 48V?

    I'm considering a small QO panel to replace the rather messy homemade fusebox on my 12V system, and QOT's would be very helpful for fitting everything in.

    Searching around on Square D's site, I wasn't able to turn up any definitive answer...

    Also, is it a problem to use these breakers with stranded (rather than solid) wire?

    thanks,
  • Robin Gudgel
    Robin Gudgel Registered Users, Solar Expert Posts: 58 ✭✭
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    Re: AC vs DC Panels and Breakers

    The RE industry has been using CBI QY series Dc breakers for 8 years now, These are the standard for DC breakers. The breakers MidNite Solar offers have been upgraded to 150VDC and come in current ratings up to 63 amps. NAWS stocks them as well as the Baby boxes to put them in. CBI breakers are made in South Africa and are the only breaker in existence that does the job. Take a look on our website for an eye opening write up on how we got that 150VDC listing. These breakers are amazing. We also now have in stock some UL listed 250VDC breakers. These are in anticipation of the release of the Classic. It looks like we will need to go back to ETL to get these breakers listed for 300 VDC as 250 will not be high enough for this controller. This high voltage DC stuff gets scary. Take a look at the wrie up. http://www.midnitesolar.com/pdfs/MidNite_165vdc_ETLtest.pdf
    Thanks,
    Robin
  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
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    Re: QOT tandem breakers OK for DC?
    jnh wrote: »
    Are the "tandem" QOT breakers (for fitting two single-pole circuits in one panel space) also rated for DC to up 48V?

    I'm considering a small QO panel to replace the rather messy homemade fusebox on my 12V system, and QOT's would be very helpful for fitting everything in.

    Searching around on Square D's site, I wasn't able to turn up any definitive answer...

    Also, is it a problem to use these breakers with stranded (rather than solid) wire?

    thanks,
    All the QO breakers up to 70 amps are rated to 48VDC. They are also ok with stranded wire.
    I am using 2 of the 100 amp panels with out any problems.
  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
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    Re: AC vs DC Panels and Breakers

    remember it may be a technicality but a qo series breaker is rated for 48 volt max so these wouldn't be rated to work on a 48 volt battery bank. As robin said with the breakers midnite and others sell i wouldn't mess with the qo stuff
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
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    Re: AC vs DC Panels and Breakers

    Square D QO circuit breakers are readily available and they are relatively inexpensive. The QO breakers are indeed rated for 48 VDC, and their AIR is 5,000 A. I would urge caution in their use.

    See: http://ecatalog.squared.com/pubs/Circuit%20Protection/Miniature%20Circuit%20Breakers/QO-QOB%20Circuit%20Breakers/0730CT9801R108.pdf

    and: http://ecatalog.squared.com/pubs/Circuit%20Protection/Molded%20Case%20Circuit%20Breakers/Thermal%20Magnetic%20Molded%20Case%20Circuit%20Breakers/0601DB0401.pdf

    They are probably best suited for combining “12 V” modules (i.e., STC Voc = ~22 V) in parallel to create a “12 V” array, or even for combining “18 V” modules (i.e., Evergreen) in parallel. However, the STC Voc of a “24 V” module is in the 44 V range (i.e., SolarWorld SW165).The Voc will approach/exceed 48 V once the ambient temperature drops below ~50 F, so the QO breaker is technically not suitable for “24 V” modules in cool-to-cold climates.

    The QO circuit breaker’s AIR (Amps Interrupting Rating) of 5,000 A DC is fairly low for use as a battery breaker/disconnect. A shorted battery could easily supply 5,000 A or more, which means that the circuit breaker could be destroyed, or, even worse, short closed. In comparison, the big DC breakers used by MidNite, OutBack, and others are rated for 25,000 A to 50,000 AIR.

    I did use QO breakers early on when my starter system was all 12 V array and 12 V battery bank. But, once I went to a 24 V / 12 V system, then a 36 V / 24 V system, and finally to a 48 V / 24 V system, all DC breakers were replaced with CBI's and Carlingswitch's from OutBack and MidNite.

    HTH,
    Jim / crewzer
  • System2
    System2 Posts: 6,290 admin
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    Re: AC vs DC Panels and Breakers

    I just found this thread in my google searches, perhaps someone can help me. I recently got a number of Kaneka panels and 5A DC CBI front-mounting breakers. I am trying to find a box for them but not having much luck. I need at least 9 knockouts, preferably 12 or 15. Do the outback front mounting boxes correspond in size?

    Any help is much appreciated.
    Nitai
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: AC vs DC Panels and Breakers

    Our host offers various combiner boxes... (if the search link works correctly).

    Otherwise, Midnite Solar makes some cost effective solutions.

    About the limits of my knowledge.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset