Circuit Breaker as a Switch

drraptor
drraptor Solar Expert Posts: 218 ✭✭
Can I use Circuit breaker as a PV disconnect switch ? Now this is silly question but what is difference btw a AC circuit breaker and DC circuit breaker ?

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Circuit Breaker as a Switch

    Yes you can.

    AC circuit breakers have an "easier time" of stopping an Arc. DC arcs are actually quite a bit more stable.

    So AC breakers are usually either rated for DC, but at less voltage and current interupt levels... Or the DC breaker are larger/heavier contacts, use a magnet to "blow away" the arc, etc. (more or less, DC arcs will sustain at voltages >~12 volts).

    As long as the breaker is rated for the working voltage (AC or DC as appropriate) and current levels (amps interrupt current), they will work just fine.

    Breakers will probably wear out sooner if used daily/multiple times a day as a switch--But for random switching operations, they are fine, and are (many times) cheaper than a switch + fuse/breaker.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Circuit Breaker as a Switch

    Yes you can use a circuit breaker as a DC disconnect. Providing it has the proper ratings for current, Voltage, and current type.

    This is why there is a difference between AC and DC ratings: it is 'easier' to interrupt AC because the nature of it is a Voltage waveform which crosses zero Volts 120 times per second. In essence AC turns itself off, so the disconnect is more a matter of 'keeping it off'. DC does not have this rise and fall of Voltage, which makes it easier to sustain an arc across contacts as they open.

    In the case of the Square D QO (Quick Open if you were wondering) they are rated for up to 48 VDC. Do not confuse this with being able to work properly on a 48 Volt system, because the actual Voltages on such a system can be much higher than that (60 Volts on the battery side is not uncommon and 70 Vmp on the array or more).
  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    Re: Circuit Breaker as a Switch

    It is fairly common for circuit breakers to act as light switches in warehouses, stores, and commercial environments. It is OK to use a circuit breaker as a switch if the following ratings are listed on the breaker.

    HID This rating indicates a breaker can be used to switch fluorescent lights on a regular basis
    SWD This rating indicates a breaker can be used to switch HID and fluorescent lights on a regular basis

    Yes, breakers are commonly used for PV disconnects, but they have to be rated for it and DC voltage ratings are generally much lower than AC ratings. I think the highest DC ratings for breakers I've seen are 150Vdc. For arrays higher than that, you have to go to pull-out fuses. Another trick I've seen for DC disconnects is to use a multiple throw switch and put more than one switch contact in series.
  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    Re: Circuit Breaker as a Switch

    I want to use it as cheap alternative to DC switch, it will also allow me to disconnect the PV array during battery swtich over (I have spare 150AH FLA laying around) .

    this factory is using the circuit breaker to protect the CC.

    CLincAK.jpg


    Their system setup

    P4Q6AqC.jpg

    They also sell SolarWorld panels
    pTxQbWk.jpg

    How do you mount these panels ? there are only 4 mounting holes on this large 250W Polycrystalline panels
    CnNsbsB.jpg
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Circuit Breaker as a Switch
    solarix wrote: »
    ...Another trick I've seen for DC disconnects is to use a multiple throw switch and put more than one switch contact in series.
    That would be a multiple pole switch. :)
    And the DC breakers available through Midnite Solar are, I believe, rated for a DC voltage higher than 150V. The problem with the original ones they offered (and maybe the current ones) is that they are polarized and so cannot be installed for both disconnecting under load and safely breaking reverse fault current from the batteries. :(
    SMA SB 3000, old BP panels.
  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    Re: Circuit Breaker as a Switch
    inetdog wrote: »
    That would be a multiple pole switch. :)
    (
    any pictures of that multi pole switch ?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Circuit Breaker as a Switch
    drraptor wrote: »
    any pictures of that multi pole switch ?

    A multi-pole switch is like two or more single-pole switches ganged together to work simultaneously.
    Multi-throw (usually double-throw) refers to the switch have more than just on/off function (as in normally open and normally closed contacts).

    Sometimes double-pole switches are wired in series to increase Voltage handling (the gap of two contacts open will resist higher Voltage arcing). This is done with varying degrees of success and code compliance.

    You can have a lot of fun with switch acronyms: SPST, SPDT, DPST, DPDT ....
  • nsaspook
    nsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Circuit Breaker as a Switch
    drraptor wrote: »
    any pictures of that multi pole switch ?

    I use an old three pole heavy-duty 30hp motor disconnect series wired for my solar feed disconnect but a proper switch
    would be something like this.
    https://www.platt.com/CutSheets/Eaton/SafetySwitches-Solar-DCGSeries-CutSheet.pdf
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Circuit Breaker as a Switch
    inetdog wrote: »
    That would be a multiple pole switch. :)
    And the DC breakers available through Midnite Solar are, I believe, rated for a DC voltage higher than 150V. The problem with the original ones they offered (and maybe the current ones) is that they are polarized and so cannot be installed for both disconnecting under load and safely breaking reverse fault current from the batteries. :(

    The 300 volt Midnite breakers are double wide because they are two 150 volt breakers, in series, ganged together somehow.

    I wonder if you could make a 150 volt non polarized breaker by ganging two of them together, in series, with opposite polarity.

    btw, the polarized Midnite breakers are their din rail breakers. Their panel mount breakers are NOT polarized.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i