DC Breaker Question

rake1 Solar Expert Posts: 173 ✭✭
Just a quick question I am at my camp and setting up my Fm60 and was putting the Dc breaker between the Battery and the Fm60 and I just scratched my head. I assume it makes no difference which way I hook up this breaker,  I an assuming the breaker is generic so if I put the wire from Fm60 on the top of breaker or the bottom of the breaker it makes no difference.Please clarify this for me just to be safe


  • Vic
    Vic Solar Expert Posts: 3,207 ✭✭✭✭

    Hi rake1,

    It can matter,   what connects to which breaker terminal.

    What is the brand and model number of the breaker?

    Thanks,   Vic

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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Sometimes DC breakers have a terminal marked LOAD.   Getting this correct is important, because a DC breaker has an ARC CHUTE that disperses the arc that is generated. otherwise its possible to have the arc not quench and current keep flowing
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    doesn't have anything on it I do see a small + on the top of the switch
  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    I looked closer at the switch and it does have a small + Just above the switch, So if that is the case then the power should enter at the top correct. Charge controller in the top +, and battery on the bottom. Array into the top + and charge controller out the bottom. Am I correct? Not sure if you can see the plus in this PIC.
  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    edited April 2018 #8
    I does indicate the + is at the top of the breaker, Found this explanation here on the forum, not your breaker, but should be wired the same.

    The MNEPV din rail breakers do have a polarity. The + on the bottom side of the breaker means it wants to be hooked up to the highest potential. That will be the PV+ in a combiner or to the battery + when connected to the output of the controller. Now you may think that the output of the controller is at a higher potential than the battery plus terminal. Wrong! When a controller fails it shorts battery + to battery -. The battery+ terminal is the real highest potential when the controller fails. That condition is when you need the breaker to trip. I have found that unless you are at the top end of the voltage rating and at very high current, these din rail breakers trip just fine even hooked up backwards. Do it right though. It doesn't cost any more."

    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    So what you are saying is put the source with the highest possible voltage to the + side of the breaker, as you mentioned Battery on + side controller on the other, and array on the + side controller on the other. Correct? You know I have got so many different answers to this question I am confused. Some say they are polarized and can only go in one direction some say they are not Polarized. Just wondering if maybe BB would chime in on this on also. Raj174 thanks for your input.
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    The side with the highest potential energy, not voltage, the battery can produce far more energy in a short circuit condition than the charge controller, which is limited to its maximum output current, the battery on the other hand can provide hundreds if not thousands of amps, depending on its capacity. So the battery would be attached to the + or terminal 1, the controller on terminal 2. 
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    Thanks Mcgivor, my concern here is do we know for sure that these breakers can let current through in both directions. Hooking it up as you say would be fine, but the charge controller is sending current to the battery constantly can it still do that with the positive on the battery side. and will it trip if the charge controller malfunctions or sends to many amps through the breaker.
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    It will function normally (pass operating current from the CC to bank) with the + terminal on the bank positive.

    If/when the controller fails, a common failure mode is apparently a short, in which case the battery is the current source, not the controller. Unless you're really massively overpanelled on the controller, there's no other source of current comparable to what the bank can produce into a dead short. This is why you want to orient the breaker as above.
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    edited April 2018 #13
    Thank you Estragon, so the same with the Array then Positive on the array side correct? found this in the meantime thanks Estragon confirms what you said.