shutoff switch between panels and charge controller (2000W 24V offgrid)

[joe luser]

Hi,
Beginner here and my first question. I'm building essentially the "classic 2000W 24V system" with ground mount panels for an off-grid cabin. It *seems* like there should be a shutoff switch between the panels (located 30 feet outside the cabin) and the charge controller (located inside the cabin).

The blueprints do not specify any such thing. And it's not clear to me what I would use if I were to want to install a switch. I'm wiring the 4 100W/6A panels in series-parallel and using #6 wire for the run between pv and cabin, so there will be no danger of exceeding the ampacity of the wire, if that matters.

What's the consensus and/or electric code say about disconnect switches or breakers?

Thanks!
joe

 

[Fred S]

You should have a disconnect of some kind, often it's a breaker. A DC breaker in that voltage and amp range is pretty inexpensive.

 

[Popuptoaster]

I have an automotive battery isolator switch in the positive feed from the panels on my boat, seems to work OK, dunno if it's an "approved" method though, I'm a beginner too!

 

[joe luser]

Thanks! I had looked at that battery isolator switch, and it seems cheap and effective. Is there any reason to want to disconnect *both* positive and negative? Like, say, if the 12VDC from the panel was +-6VDC referenced to ground, then the negative wire would still be hot at the charge controller. Or i may just may be confused about DC?

 

[joe luser]

Or no. Thinking out loud .. please correct me if this is wrong .. the negative post of the charge controller is connected to the negative post on the battery which in turn will be connected via thick copper grounding wire to earth. So there should be no need to disconnect the negative wire from the panel?

 

[Craig]

I always disconnect both as it is what I have seen in most SCC manuals I have looked at.

 

[sunshine]

series-parallel

Is that 2x2?? Most likely that would be under 48volts and possibly not subject to any code. You will need to check for your particular locality.
If outside any regulations why bother? The amperage is limited to the panels output and the cable rating should be well above this.
Safely route your cable and mount charge controller on fire proof substrate.

 

[Popuptoaster]

Wills parts pages list 60amp RC model battery connectors that he puts on his wires so he can just unplug the panels from the CC, i did get a bag of them when i got my parts but even though I only have 2 250W panels I used the quite chunky solar panel wire you see on houses so the plugs were a bit small which is why i fitted the switch, I had it laying around and it's way over spec for my panels.

 

[SolarQueen]

@Fred S has the correct answer. Although overcurrent protection probably isn't required for 2 strings, a disconnect is. Use a breaker on the positive between the panels and the charge controller for both over current protection and a disconnect. The Isc of each string is probably around 5.75 x 2 strings x 1.56 (over irradiance and 25% oversize requirements) = 18A, round up to 20A breaker. Do not disconnect the negative.

 

[MichaelK]

I use Midnight controllers, so I don't feel guilty pirating their controller wiring diagram. I followed this for wiring together my own systems. Looking at the diagram, there's a series of two sets of breakers between the panels and the controller. The first set of breakers is at the combiner box (#11) which has a breaker for each solar "string". Each string could be switched off individually, for maintenence for example. The second breaker (#16) shuts off ALL the solar strings.

They sell a box designed to hold all the breakers and wiring. It's called an E-panel, or sometimes power center. I have them for both my systems. It's the second pic below. They make the installation much safer and more professional looking. Note that they make brand specific power centers. So, a power center designed to work with Outback products, won't look the same as a power center designed to hook up a Schneider unit.

 

[Pacer]

@Fred S has the correct answer. Although overcurrent protection probably isn't required for 2 strings, a disconnect is. Use a breaker on the positive between the panels and the charge controller for both over current protection and a disconnect. The Isc of each string is probably around 5.75 x 2 strings x 1.56 (over irradiance and 25% oversize requirements) = 18A, round up to 20A breaker. Do not disconnect the negative.

Great info- why not disconnect the negative? Thanks!

 

[SolarQueen]

In a grounded system, the negative is connected tot the ground. If you disconnect the negative, you disconnect its path to ground.

 

[Pacer]

Thank you for the clarification!