DC Disconnect for 4 sub-arrays

[robomartin]

I spent an hour with a very helpful electrical plan checker at the LA County Building and Safety office. They want a DC disconnect switch right at my ground mount array due to the fact that you can't see the inverters from the array. I get it and, frankly, I want the disconnect myself.

Here's the problem: I need 8 poles (8 switches) in order to be able to disconnect the four 10-panel sub arrays I am installing. The disconnects I keep finding are all three pole.

Hopefully someone has visited this territory before me. Any recommendations?

It has to be UL listed and outdoor rated.

Another desired feature is that the entire thing be compact. I want to mount it on the back of an 8 x 8 inch pole and ideally not have it stick out the sides too much.


Thanks,

-Martin

[sensij]

Make sure that anything you are looking at is rated for 600 V DC. They tend to be more expensive than the AC disconnects you find in the box stores.

Check out Midnite Solar's disconnecting combiners. This one is intended for your 4 string application, but you might want to go with a pair of 2 channel disconnects if it fits the space better.

http://www.midnitesolar.com/productPhoto.php?product_ID=582&productCatName=Combiners%20-%20Disconnecting&productCat_ID=26&sortOrder=5&act=p

[robomartin]

Make sure that anything you are looking at is rated for 600 V DC. They tend to be more expensive than the AC disconnects you find in the box stores.

Check out Midnite Solar's disconnecting combiners. This one is intended for your 4 string application, but you might want to go with a pair of 2 channel disconnects if it fits the space better.

http://www.midnitesolar.com/productP...tOrder=5&act=p

I'll take a look, thanks. I don't need combiners. The SMA inverters I am using have three input channels each. I am wiring each of four sub-arrays directly to the inverters and need switches in between.

[sensij]

I'll take a look, thanks. I don't need combiners. The SMA inverters I am using have three input channels each. I am wiring each of four sub-arrays directly to the inverters and need switches in between.

Yes, the model I linked would work for two of your four strings, there is no combiner in that one (that is just the category on their site in which it is listed). You'd need two of those. They have other (bigger) models that would handle all 4 of your strings.

[DanS26]

Maybe, if you are handy enough, you could build your own.

Find a NEMA 3R rated enclosure with a lockable door. Install a DIN rail and eight touch less fuse disconnects on the rail inside along with a separate ground bar.

You want a lockable door to keep out anyone unauthorized from disconnecting your strings under load. Not a good thing with DC power. Just make sure your design passes muster with AHJ.

Yes it is not readily accessible but your transformer-less inverter should switch both positive and negative at the inverter which is readily accessible.

[robomartin]

Maybe, if you are handy enough, you could build your own.

Find a NEMA 3R rated enclosure with a lockable door. Install a DIN rail and eight touch less fuse disconnects on the rail inside along with a separate ground bar.

You want a lockable door to keep out anyone unauthorized from disconnecting your strings under load. Not a good thing with DC power. Just make sure your design passes muster with AHJ.

Yes it is not readily accessible but your transformer-less inverter should switch both positive and negative at the inverter which is readily accessible.

I have access to a machine shop so this would not be a problem. I need to check with the county to see if this DIY approach would be acceptable to them. Thanks.

[ButchDeal]

If you have not (damn forum rules that block any post by an Apple product with an appostrafi) purchased the inverter you might consider going with solaredge which would reduce the strings by using longer optimized steings

you can also eliminate the switch by using the remote firefighter button that would trigger the inverters built in rapid shutdown

[DanS26]

Oh, and by the way, if you DIY it will be significantly less cost...........

[bcroe]

I spent an hour with a very helpful electrical plan checker at the LA County Building and Safety office. They want a DC disconnect switch right at my ground mount array due to the fact that you can't see the inverters from the array.

Here's the problem: I need 8 poles (8 switches) in order to be able to disconnect the four 10-panel sub arrays
I am installing. The disconnects I keep finding are all three pole.

It has to be UL listed and outdoor rated. -Martin

Seems to me, you should consider a combiner box at the array, with a single disconnect switch
next to it. I am using 2 poles of 3 pole 600 VDC switches here. Came in handy when one
burned out, just moved the wires over to the unused pole. Expensive, but mine appear on
Evil Bay at affordable prices. Bruce Roe

[Mike90250]

Maybe, if you are handy enough, you could build your own.

Find a NEMA 3R rated enclosure with a lockable door. Install a DIN rail and eight touch less fuse disconnects on the rail inside along with a separate ground bar.
You want a lockable door to keep out anyone unauthorized from disconnecting your strings under load. Not a good thing with DC power. Just make sure your design passes muster with AHJ.
Yes it is not readily accessible but your transformer-less inverter should switch both positive and negative at the inverter which is readily accessible.

But ya gotta be sure it's all DC rated. By the time you spend $$ for the touch less fuses & disconnects, would ganging breakers do the same thing for less ?

[DanS26]

But ya gotta be sure it's all DC rated. By the time you spend $$ for the touch less fuses & disconnects, would ganging breakers do the same thing for less ?

Here is the fuse holder I would recommend......

https://cdn.allfuses.com/media/documents/Ferraz%20USM%20Fuse%20Holders.pdf

Rated for both AC and DC. Cost as low as $6.98 per holder.....it doesn't get any better.

[bcroe]

Here is the fuse holder I would recommend......

https://cdn.allfuses.com/media/docum...%20Holders.pdf

Rated for both AC and DC. Cost as low as $6.98 per holder.....it doesn't get any better.

I see on the sheet, NO-LOAD DISCONNECT. I think these (which are used here at 400VDC)
are capable of opening a HV DC circuit by blowing a fuse, getting the fuse replaced, and closing
the circuit again. I think they SHOULD NOT be used to disconnect a full power circuit, not sure
if it would even work, or just start arcing. Bruce Roe

[DanS26]

As I said earlier....you do not open these fuse holders under load unless it is an emergency.....then you are really not concerned about arcing because you have bigger problems at hand.

[Mike90250]

As I said earlier....you do not open these fuse holders under load unless it is an emergency.....then you are really not concerned about arcing because you have bigger problems at hand.

That is a super BAD engineering practice and I hope the building department is able to catch it. The big problem is - what if the arc does not quench ? Well, it might when the inverter starts to glitch and drops the load, but you still have the expense of buying fuses for the holders. 600V rated DC fuses may not come in midget sizes. Always nice to do it properly.

I love the idea of the remote fireman's disconnect switch wired in.

[DanS26]

Midget DC fuses come in both 600V and 1000V sizes in a good range of amps. I have used both. I have never blown a DC fuse while disconnecting....of course I have never tried to disconnect under load.

Even the string inverter manufacturers recommend to not operate their built in DC switches under load. But then again what makes sense and common practice among electricians is completely oblivious to the general public. Then again the general public gets to pay the repair bills.