Author Topic: DC Disconnect Switch vs Breaker?  (Read 40 times)

ligwyd

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DC Disconnect Switch vs Breaker?
« on: July 02, 2018, 11:55:46 AM »
Hi there,

If have the below Midnite DC disconnect:
http://www.midnitesolar.com/productPhoto.php?product_ID=250&productCatName=Mini%20%20DC%20Disconnect&productCat_ID=8&sortOrder=8&act=p

Has anyone every considered installing a simple on/ off switch in the place of the 250 A breaker? Reason I ask this is that I already have a 250 A breaker in the distribution panel and my 3 battery strings in my bank will all be separately fused. I wonder if there is much of a cost saving in using a switch instead of a breaker in the DC disconnect? If not I can use the 250 amp breaker in the DC disco as an off switch, which is what it was originally planned to be used as,  to neutralize any incoming power from the battery bank if I need to get my hands in t the inverter/ distribution panel. Just throwing it out there to get someones thoughts on this?

Thanks

ClassicCrazy

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Re: DC Disconnect Switch vs Breaker?
« Reply #1 on: July 02, 2018, 12:06:08 PM »
You can use the breaker to switch off the inverter .
I forget what kind of inverter you said you had. On my outback inverter it has contacts that you can put in a remote switch. That does not turn all the power off to the inverter but shuts down the inverter . I have mine with a regular switch and a timer switch in parallel so I could have the inverter shut off automatically after a certain amount of time. You could also use a relay or the contacts on controller to shut off the inverter that way.   Using a breaker to shut off an inverter under load is a bit different but they are designed to be able to handle the DC arc that will happen inside of them if they were shutting off the full 250 amps . You can't replace the breaker with a regular switch because the breaker is designed to cut the power automatically on an overload. A switch does not do that. And considering that there are such large wires going to the inverter and through the breaker there is no way you could connect those to a regular switch. Remember the breaker is there to protect the wire from getting hot and melting or starting a fire on an overload. Switches don't do that function.

Larry WT9M 
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

ClassicCrazy

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Re: DC Disconnect Switch vs Breaker?
« Reply #2 on: July 02, 2018, 12:09:22 PM »
It would help if you could draw out the wiring along with breakers and wire sizes for us to understand how your system is wired up.

Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie