Load vs Line side of Circuit Breaker

gkerlin
gkerlin Solar Expert Posts: 27 ✭
in General Solar Power Topics #1
Ok. this might seem like a really dumb question but.... This is an install on my Motorhome. I've got some dc breakers to install on either side of my controller. The connections on the breaker are marked "load" and "Line"

In a house - its easy - the line is the street side. On my Motorhome the house battery bank is the line side.

So - the DC Breaker between the house batteries and the controller has the line side connected to the batteries, and the load side to the controller. At least that's how I see it.

The PV side is a bit more confusing. I have several breakers on that side of the controller as well. Is the PV array side of the breaker the line or load side of the breaker? On one hand I see the PV side as line since it supplies the current. But if I had a malfunction and the batteries started pushing current thru the controller to the panels there is more potential for damage in that direction.

What is the accepted norm? Am I over thinking it?
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #2
    gkerlin wrote: »
    So - the DC Breaker between the house batteries and the controller has the line side connected to the batteries, and the load side to the controller. At least that's how I see it.

    that is correct.
    gkerlin wrote: »
    The PV side is a bit more confusing. I have several breakers on that side of the controller as well. Is the PV array side of the breaker the line or load side of the breaker? On one hand I see the PV side as line since it supplies the current. But if I had a malfunction and the batteries started pushing current thru the controller to the panels there is more potential for damage in that direction.

    Correct again... the line side goes toward the controller and the battery. This breaker is sized large enough that your panels can never trip the breaker. If it trips, it's battery current that trips it.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #3
    On the PV side the panels are a current source, so are considered a 'line' side if you re using POLARIZED breakers...at the CC the line side is to the battery... There are new MidNite DC breakers now that are non polarized, and can be installed in either direction.

    hth
     
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #4
    vtmaps wrote: »

    that is correct.



    Correct again... the line side goes toward the controller and the battery. This breaker is sized large enough that your panels can never trip the breaker. If it trips, it's battery current that trips it.

    --vtMaps
    That is correct if you have installed the CB for protection only. If you are also going to use it as a switch to disconnect the panels while they are producing current, then the breaker may not survive very many cycles. The ability to have one breaker properly rated for both purposes is one reason that Midnite made an effort to find non-polarized breakers.

    PS: The reason many DC breakers are polarized is that they use a permanent magnet and an arc chute to interrupt the DC arc across the contacts as they open. If the current is in the wrong direction the arc moves back into the breaker mechanism instead of into the arc chute.

    The actual trip mechanism is usually not polarity sensitive, so the breaker would open at about the same current in either case. The question is what happens to the poor breaker once it trips. :-)
    SMA SB 3000, old BP panels.
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #5
    And if they are labelled load and line they are most like carling breakers (which are pretty much all non polarity sensitve). Line/load labelling just to stop people asking which is which.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #6
    inetdog wrote: »
    That is correct if you have installed the CB for protection only. If you are also going to use it as a switch to disconnect the panels while they are producing current, then the breaker may not survive very many cycles.

    In many cases it makes sense to wire the breaker as a switch and not worry about battery current tripping it. There is already a breaker between the battery and controller, and as long as that breaker is sized to protect BOTH the battery-controller cable and the combiner-controller cable, you shouldn't need over-current protection in the combiner-controller cable.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • davemac
    davemac Registered Users Posts: 39 ✭✭
    #7
    ...and does it follow for the fused disconnect between the battery and inverter that the line is battery side and load on the inverter side?
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
    davemac said:
    ...and does it follow for the fused disconnect between the battery and inverter that the line is battery side and load on the inverter side?
    Yes, the inverter is the load.  --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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