DC breaker for AC

fatheadl
fatheadl Solar Expert Posts: 31 ✭✭
in General Solar Power Topics #1
Hi all,
Is it ok to use a 15ADC breaker for a 15AAC application?

Thanks in advance
fatheadl
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: DC breaker for AC
    fatheadl wrote: »
    Is it ok to use a 15ADC breaker for a 15AAC application? l


    ONLY if the breaker carries dual ratings. What might open on a 24V DC circuit, may just arc at 120V. I believe there are some dual rated breakers made.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #3
    Re: DC breaker for AC

    Square D QO series breakers are the only ones that I know of in general use that are approved for DC voltages up to 48vdc. Most general breakers are AC rated.

    Icarus
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  • fatheadl
    fatheadl Solar Expert Posts: 31 ✭✭
    #4
    Re: DC breaker for AC

    Hi all,

    I ordered AC breakers and was sent PV DC breakers. I was told by the store that they should work. I just want to make sure.

    fatheadl
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #5
    Re: DC breaker for AC

    What are they? Brand, mod # etc.

    Icarus
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  • System2
    System2 Posts: 6,290 admin
    #6
    Re: DC breaker for AC

    due to the nature of AC to DC its not recomended to use breakers designed for one operation to another unless specifically noted they can handle those. Usually this is more so true using AC breakers to DC as DC often carries a higher amp at a lower volt and the amps is what causes jumping and shorting from what i understand someone told me.
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  • fatheadl
    fatheadl Solar Expert Posts: 31 ✭✭
    #7
    Re: DC breaker for AC

    Hi Icarus,

    I think they are midnite solar MNEPV15

    fatheadl
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #8
    Re: DC breaker for AC

    The difference is that DC tends to arc when the circuit is opened. As I understand it (which is only a bit!) : DC is "on" 100% of the time, therefore you are breaking the circuit at full load and the current tries to "jump" the gap as the breaker (switch) is opened.

    AC on the other hand cycles "on/off" 60 cycles per second (in N America) From what I was told (I'm not an engineer!) is that because of the phase cycle, as you open the circuit, it is effectively off for ~1/2 the time, and ergo the voltage doesn't have as much chance to arc.

    The problem is then the danger of the arc, ie explosive environments etc, and the switch points tend to get pitted and can weld themselves open (or shut) defeating the breaker or switch.

    My hunch is that in low voltage/low amperage system using a DC rated breaker would do no harm. Higher currents I would err on the side of using the proper rated device.

    I'm sure the real genius's here will correct my crude description.

    Icarus
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #9
    Re: DC breaker for AC

    Fatheadl,

    Midnite's DC breakers are manufactured by CBI. You might try looking around their website for more information. The CBI part number is printed on the white label on the side of the breaker. It seems to me that the "QY" are rated for DC applications, but carry no AC specs.

    See: http://www.cbibreakers.com/

    HTH,
    Jim / crewzer
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  • fatheadl
    fatheadl Solar Expert Posts: 31 ✭✭
    #10
    Re: DC breaker for AC

    Hi all,

    I have contacted the store that sold the breakers, and is now being told that they do not sell AC breakers, so whenever AC breakers are ordered, they ship the DC breakers instead. If they do not sell AC breakers, why would they display AC breaker listing on their web site? Is this a right way to do business? To get a refund, it is gong to cost me shipping to send them back.

    fatheadl
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #11
    Re: DC breaker for AC

    Based on the scenario you've described, I would take a different tact. In my view, the breakers that were shipped were not the ones you ordered, so you have no obligation to pay for them. If the vendor can't supply what they advertised, then they can send a pre-paid shipping label to you to return the breakers, and they can also credit your payment.

    HTH,
    Jim / crewzer
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  • kc8adu
    kc8adu Solar Expert Posts: 50 ✭✭✭
    #12
    Re: DC breaker for AC

    a dc rated breaker in most cases will be fine in a ac circut.
    the problem is that it may not pass inspection and if you have a fire your insurance may use the part being unrated for ac service as basis for denying a claim.
    not worth it.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #13
    Re: DC breaker for AC

    Be careful about the DC rated breakers--it is not easy to say whether or not that DC breaker would be safe you your application... The typical AC breaker is rated for ~600 VAC of breakdown voltage and is tested to something like 1,800 VAC (line to ground)...

    A 60 VDC rated breaker is probably not tested to 1/10'th that voltage. Can be damaged/fail due to surges/lightning strikes if you are using this on a standard 120/240 VAC distribution system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    #14
    Re: DC breaker for AC

    Do you know which AC breaker you actually ordered? If you ordered it online I can look it up with an order number.
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