Circuit Breakers, Fuses, Disconnects Oh My

micahvmicahv Registered Users Posts: 17
First question,
Square D QO series that I find in Home Depot, are they DC rated? They don't state DC on the actual breaker, but I reading the square D specs it sounds like they are 48V up 70A for 1-2Pole and 60A for 3 pole? If this is the case this would be convenient to have a local source.

Next is the different types of mounting options? DIN, Panel Mount, others? If I buy some square D circuit box at Home Deport will I run into issue trying to use say a DC breaker I buy from W&S? Why such a wide price range in similarly rated breakers?

Third, Can I use a breaker anywhere I can a Fuse? Is price the main issue? Seems so much simpler to just use a breaker cause then I have a disconnect and a breaker? I guess also fuses can tolerate more hostile environments like on a roof for a combiner box?

Fourth, poles? I guess I want 1 pole if I'm running a small stand alone system? When I was looking at Home Depot today I saw some Square D breakers that had two breakers in one body. DIN mount that snapped in with a common conductor at the top and 2 in the bottom. The cirucit box I was looking at only seem to work with this kind of breaker. It looked like the breaker would trip independently...and I thought 2 pole tripped together?

Any good recommended online sources for learning more about this stuff?

Thanks for some clarification,

Micah

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    First, you seem to be blending AC & DC. Only DC rated fuses and breakers should be used with DC. It's much more difficult to make a 'clean' disconnection with DC - it wants to 'jump the gap'. This has to be allowed for in designing the device in question.

    Yes, breakers can be used in most places where a fuse can be. As you said, there's the added advantage of built-in disconnect. But they are less "climate hardy", and what's the point of using a more expensive device where you only need circuit protection such as up on the room in an array combiner?

    As for AC, the breaker mountings tend to be proprietary to the manufacturer. "Can't put a square peg in a round hole" sort of thing. Almost all AC boxes alternate the input side of the breaker from 'Pole 1' to 'Pole 2', so that a double pole (240 V) breaker can plug into two adjoining spaces. This type of breaker has one 'double' switch in it which trips both side simultaneously. There are "dual" breakers which are just two 120 V units in one case. There are also GFI brekaers and Arc-fault breakers ... and Lions and Tigers and Bears! :p

    It is confusing, isn't it?
  • micahvmicahv Registered Users Posts: 17
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    Thanks for the reply, and yes it is confusing :) As for the AC vs. DC I am aware AC/DC breakers are not interchangeable. I had heard from someone that the Square D QO could be used with DC. I then looked up the QO series spec sheet, http://tinyurl.com/y97am3c and it has QO rated for 48V? It makes a sense that since the issue with DC is the spark jumping a wider gap that an AC rated breaker could safely handle lower voltage DC?

    As for poles, I'm still confused as to the breaker I mentioned 2 in one body sharing a common conductor at the top with two conductors coming out the bottom. These will both trip simultaneously? If so if I manually throw one breaker does the other one go?

    Thanks
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    According to that link, these breakers are rated for DC (except the 10A?). Always trust the manufacturer over "some guy" - even if that guy is me. Especially if it's me! :p

    If the breaker has ONE input, TWO 'trip bars' and TWO outlets it's a single pole double breaker. They won't be common trip. The 240 V breakers have two inputs (one for each pole) a 'double trip bar' (like two singles joined together - some have only one 'switch') and two outlets.

    When in doubt as to its design/function, get the model number off it and 'Google' it. :D
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    48 VAC is not the same as 48 VDC. So even though the breaker is rated for 48v, that doesn't mean it can properly handle DC. Always check the specs.

    Sometimes, you want a fuse instead of a breaker - usually if you have a need for a "fast blow", "slow blow" or "time delay". You can get breakers that do that, but they aren't just more expensive, they are a LOT more expensive.

    http://en.wikipedia.org/wiki/Fuse_%28electrical%29

    As for poles, I'm still confused as to the breaker I mentioned 2 in one body sharing a common conductor at the top with two conductors coming out the bottom. These will both trip simultaneously? If so if I manually throw one breaker does the other one go?

    That type will NOT both trip at once. They are commonly known as a "split" breaker. Two separate breakers in one body. Most are the width of a standard breaker, and are used to squeeze more breakers into a full panel. They don't need to be tied together, since both breakers take their feed from the same phase - so they can't be used as 220 breakers.


    A dual (220v) breaker that is designed to trip both legs will have the handles "tied" together by some mechanical means - such as a peg which goes into both handles and has a bump in the middle so it can't slide out, or a clip which fits over both handles to tie them together.

    There are also dual breakers with just one handle. These are internally tied and so when either leg trips, both will shut off (if the breaker is working properly).

    I have seen installers make a dual breaker in a pinch by taking two single-phase breakers, installing them next to each other, then running a long 6/32 screw through the holes in the handles to tie them together into a single 220 breaker.
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    Dc breakers are a different animal I highly recommend you stick with stuff like the panels from www.Midnitesolar.com or other manufacturers. Also the big difference between fuses and breakers is voltage a fuse can handle 6-700 volts where a typical breaker would have a limit of 150 volts although Midnite did just get listing on there 300 volt dc breakers.
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My
    micahv wrote: »
    Thanks for the reply, and yes it is confusing :) As for the AC vs. DC I am aware AC/DC breakers are not interchangeable. I had heard from someone that the Square D QO could be used with DC. I then looked up the QO series spec sheet, http://tinyurl.com/y97am3c and it has QO rated for 48V? It makes a sense that since the issue with DC is the spark jumping a wider gap that an AC rated breaker could safely handle lower voltage DC?
    Thanks

    The QOU breakers are DC rated to 48 volts. The QO breakers - which is what 99% of all hardware stores carry - are not.

    However, for any current installation we recommend the Midnite Solar/Outback Power type DIN rail breakers for most DC applications. As a general rule, breakers for off grid battery based systems and fuses for grid tie high voltage systems.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    More on QO breakers and DC applications:

    See: http://www.squared.com/us/misc/faqInter ... light=0,DC

    and: http://www.squared.com/us/misc/faqInter ... light=0,DC

    and: http://www.squared.com/us/misc/faqInter ... light=0,DC

    and: http://www.squared.com/us/misc/faqInter ... light=0,DC

    and: http://www.squared.com/us/misc/faqInter ... ight=0,QOU

    There are nonetheless some concerns to address. One is that the breaker’s DC ratings are not typically included with the breakers. For example, the ones in my "inventory" carry only AC rating info. An inspector might reject a CB without marked DC ratings. The breakers can be ordered from Square D with DC rating labels.

    Note that the DC voltage ratings are absolute. IOW, a designer must consider actual system and/or NEC calculated voltages, and not just “nominal” voltages.

    Another concern is that these breakers’ AIR (Amps Interrupt Rating) is usually reduced from 10 kA to 5 kA for DC applications. This reduced rating is probably OK for PV array combiner applications. However, it’s way too low IMHO for applications where the breaker is connected directly to the battery, as a battery bank could easily supply >5 kA during a short.

    The Carlingswitch F-Series DC-rated circuit breaker is often used for a main battery CB. Its AIR is 50 kA.

    HTH,
    Jim / crewzer
  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    S
    Square D QO series that I find in Home Depot, are they DC rated? They don't state DC on the actual breaker, but I reading the square D specs it sounds like they are 48V up 70A for 1-2Pole and 60A for 3 pole? If this is the case this would be convenient to have a local source.
    It is my understanding that the Square D QO series are rated at 48 Volts DC which makes them suitable for a 24 volt DC system. I use them along with the 6 breaker QO series panel for both a combiner box and for DC and AC distribution panels. Use a different box for the AC distribution. Also the QOO series is rated as a switch as well as a fused breaker. You will need higher rated breakers for both the battery and inverter disconnects.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My
    It is my understanding that the Square D QO series are rated at 48 Volts DC which makes them suitable for a 24 volt DC system. I use them along with the 6 breaker QO series panel for both a combiner box and for DC and AC distribution panels.
    I don’t agree with much of this statement.

    As noted above, the reduced AIR spec (typically 5kA) is too low IMHO for a battery breaker. A battery bank can easily supply >5kA if shorted to ground, and this fault could melt the insides of such a breaker. Such a failure could continue to conduct current rather than interrupt it.

    Another issue with “48 VDC” breakers and a “24 V” system is that such systems typically use PV array rated at “24 V” nominal or higher. However, the STC Voc of a “24 V” module (usually 72 cells in series) is typically ~44 V, and a temperature correction factor of just 110% will push such a module’s Voc to over 48 V.

    The 2008 NEC 690 alternate TCF of 110% applies to locations with a record low temp of 40F or lower. This excludes most of the U.S. from using a "24 V" module with a CB rated for 48 VDC.

    In summary, the QO breakers are probably OK for use in a combiner box for a PV array with a temperature corrected Voc of 48 V or less. This will typically mean single modules with a nominal voltage of less than ~"22" V, or an STC Voc of less than ~40 V. However, even 40 Voc STC may be too high for really cold locations (i.e., -40 F).

    Small "cabin" and RV applications come to mind. A specific example would be to use "60 cell" Canadian Solar PV modules (in parallel), QO circuit breakers, and an MPPT charge controller to charge a 12 V battery bank.

    Other "odd" voltage modules with <40 Voc STC to consider include:

    Kyocera 180 (48 cells)
    Kyocera 205 (54 cells)
    Mitsubishi (50 cells)
    Sharp 216 (60 cells)

    As previously stated, the safe and reliable approach is to use correctly spec’d DC breakers available from OutBack, MidNite, or similar. They're typically manufactured by CBI. Their ratings are typically in the 125 VDC to 150 VDC range, and a few go higher.

    HTH,
    Jim / crewzer
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    Previous post updated.

    HTH,
    Jim / crewzer
  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    Here is a link to Homepower with John Wiles take on the QO series breakers for a DC application
    http://www.nmsu.edu/~tdi/pdf-resources/cc21.pdf
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    Things have changed a bit in the RE industry since that article was published over 18 years ago in 1991.

    High-voltage DC breakers were not readily available then. Now, OutBack, MidNite, and others make these UL-listed DC-rated OCPD's readily available through their distribution and retail channels. NAWS' store, for example, is an excellent source.

    The NEC has also changed over the years. Article 690.7 is very specific about the definition and calculation of "Maximum Circuit Voltage".

    And, Wiles has updated his perspectives on using the QO breaker. See page 99 (the second sheet) of this 1998/99 article: http://www.nmsu.edu/~tdi/pdf-resources/cc68.pdf

    Regards,
    Jim / crewzer
  • bobdogbobdog Solar Expert Posts: 192 ✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    I hate to ask, but I'm using QO series breakers ina 12 volt system and if I read the thread and assoc. articles right, I'm fine using a CB for my CC to BB circuit which in turn also feeds the cabin cicuits? Did I get it right or am I in serious trouble?

    Tim
  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My
    hate to ask, but I'm using QO series breakers ina 12 volt system and if I read the thread and assoc. articles right, I'm fine using a CB for my CC to BB circuit which in turn also feeds the cabin cicuits? Did I get it right or am I in serious trouble?
    You should be fine in a 12 volt system using the QO breakers for both panel breakers and DC distribution panels. The only place they wouldn't be acceptable is for a battery or inverter disconnects due to their low AIR ratings. It is suggested to add a fuse in addition to the circuit breaker on the CC to battery connection on the battery side in case of catastrophic failure of the breaker. They would also be OK for a 24 volt DC distribution panel. For panel breakers, the Voc can't exceed 40 volts so they may not be suitable for many types of 24 volt panels.
  • System2System2 Posts: 6,290 admin
    dicsonnect load

    Hi all,
    The connectors on my solar panel instruct "do not disconnect under load".
    Does that apply to connection also?

    I'm setting up a submersible pump which connects to a controller which connects to the solar panel. The controller has a level control circuit built-in which shuts off the pump when the water reaches the contacts. Do I need to add a disconnect switch? If so where? (between the pump and controller or between controller and panel?).
    What about covering the panel as mentioned in another thread? or just submersing the leads for the level controller?

    Panel: 150w, Voc:43.6V, Isc: 4.8A.
    Controller: 180w, Vmax:50VDC, Imax: 5A
    Pump: 13-40VDC
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    i would say that would be a yes as it would apply to that too as arcs are not a good idea either way.
  • mike95490mike95490 Solar Expert Posts: 9,571 ✭✭✭✭✭
    Re: dicsonnect load
    kubio wrote: »
    Hi all,
    The connectors on my solar panel instruct "do not disconnect under load".
    Does that apply to connection also?

    I'm setting up a submersible pump which connects to a controller which connects to the solar panel. The controller has a level control circuit built-in which shuts off the pump when the water reaches the contacts. Do I need to add a disconnect switch? If so where? (between the pump and controller or between controller and panel?).
    What about covering the panel as mentioned in another thread? or just submersing the leads for the level controller?

    Panel: 150w, Voc:43.6V, Isc: 4.8A.
    Controller: 180w, Vmax:50VDC, Imax: 5A
    Pump: 13-40VDC

    I believe it means not to make/break the connections on the panels ( MC connectors ) while current is flowing, as they will arc internally, sometimes at 500VDC !
    Using a pump float switch should be fine, as the panels don't actually care.
    Of course, you pump controller/switch needs to be rated for the voltage/amps DC that you are planning to send thru it.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • System2System2 Posts: 6,290 admin
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    the controller/switch is rated for 50VDC, 5 Amps DC. The 150W panel produces 43.5 Volts open circuit and 4.8 Amps short circuit.
    they will arc internally, sometimes at 500VDC !
    With this setup I won't be anywhere near 500v, right? Does that mean I don't have to worry about arcing damage to the contacts?

    thanks
  • BB.BB. Super Moderators, Administrators Posts: 32,606 admin
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    There are several types of "arcs"... Ones that start with high voltage between two potentials--i.e., the "lightning" type where a "large" gap is jumped.

    The second is what happens when a switch opens... There is current and voltage (relatively low) and as the contacts come apart, the current attempts to arc (plasma) between the two contacts...

    That does not take very much voltage at all... 12 VDC with high available current is more then enough to sustain a pretty healthy arc (in the "old days" people would arc weld with one or two car batteries). DC is much better at sustaining an arc vs AC (which "turns off" 120 times a second as the sine wave goes positive and negative).

    So the maximum working voltage/current for a breaker (i.e., 50 VDC or 600 VAC, and maximum interrupt current--typically 5-10,000 amps for a home AC breaker, DC interrupt current is much less) is a combination of requirements--high voltage, AC/DC, Interrupt current, etc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    thanks BB,
    that's a good tip for offroad or emergency welding.
    That does not take very much voltage at all... 12 VDC with high available current is more then enough to sustain a pretty healthy arc (in the "old days" people would arc weld with one or two car batteries). DC is much better at sustaining an arc

    What I'm wondering is how many times I to have to rephrase my question before I get a straight answer ;)
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    how many times do you want us to rephrase the answer?:confused:
  • BB.BB. Super Moderators, Administrators Posts: 32,606 admin
    Re: Circuit Breakers, Fuses, Disconnects Oh My

    Trying again... Need to match the Circuit Breaker to the application.

    If a CB is only rated for AC -- then it cannot be used on DC application of any rating. DC requires much larger contacts and more exentensive construction to "quench arcs" than AC breakers do.

    So, if you have breaker that is DC rated, where it is used must be within those specifications.

    The link to the SquareD catalog (as provided earlier by micahv) does list some of the QO that can be use in a 48 VDC circuit (mostly 10a-70a single pole breakers).

    A point that Jim/Crewzer is bringing up is that single car sized 12 VDC storage battery can output ~4,000 amps into a dead short. Start putting parallel strings of large industrial storage batteries together in parallel at higher voltages, and the instantaneous current will easily exceed the QO breaker interupt rating of 5,000 amps....

    So, for small solar battery systems, and for use as string protection devices in paralleled solar array (more than two parallel strings)--the QO breakers are OK.

    However, if you have a large battery bank, the beaker in the event of a dead short, may not be able to stop the current flow (i.e., big plasma fire).

    For protective devices that sit on the main battery bus--higher interrupt rated fuses or breakers (or may be a large fuse upstream to limit current to below 5kA, and a set of smaller distribution QO breakers to your individual circuits.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,571 ✭✭✭✭✭
    Re: Circuit Breakers, Fuses, Disconnects Oh My
    kubio wrote: »
    What I'm wondering is how many times I to have to rephrase my question before I get a straight answer ;)

    The terminals, cables, and MC4 Connectors on solar panels, are NOT designed to make or break an energized circuit. Switches and circuit breakers are made to do that.

    The switches and cb's need to have a DC rating of the the voltage/amps you are designing the system to use. If you have several panels powering a pump, then the switch needs to be able to handle the max PV voltage and amps that will go thru it.

    Don't use a 12V, 10A switch for a 24V, 30A circuit.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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