Safety Switch?

jACKr

Aloha! I'm hoping to set up a safety switch that cuts power from a small array of 2 REC 320s in series.  Before it gets to a Combiner. This is a temporary scenario while I put on a new roof where my main PV lives, and use the REC320s while the other roof array is off line.
I have a small Breaker Panel that's unused. I'm wondering if anyone has ever used a Breaker as a Switch to cut DC power? If its doable? And, any caveats?
In Advance! Thanks!
jACKr

Photowhit

jACKr said:

I have a small Breaker Panel that's unused. I'm wondering if anyone has ever used a Breaker as a Switch to cut DC power? If its doable? And, any caveats?

Yes, quite common, just be sure to use DC breakers! 

Available here and elsewhere, Some are polarized requiring them to have the flow in a certain direction.

Most common are Midnightt's Din rail breakers;


Midnite Solar MNEPV 150 Volts 15 Amps DC Circuit Breaker | Northern Arizona Wind & Sun (solar-electric.com)

DC breakers are typically magnetized to help interrupt DC's stead flow.

Dave Angelini

For temporary you could use the breaker panel. If they are AC breakers they will work for awhile. You should then discard the breaker you use as DC will ruin an AC breaker over time. For 2 panels in series (about 80vdc guess) you could just use a switch from an auto store for awhile. Look for a Knife switch as a cheap and decent solution.

You really should get away from this and use the correct voltage rated DC voltage circuit breaker. Since the current is low for this solar application, most any amperage of a correctly rated 125 to 150 vdc breaker is what you want. It is just a switch and over current protection is not needed unless you have more than 2 strings of panels. You have one string here.

Alooooh haaaa !

jACKr

Aloha! I abandoned the Breaker option as a Temp safety switch.
There's no DC breakers available for the GE box I have.
I went to a real Safety Switch. But, I'm perplexed by what is hobbling me from success.
My PV array string of 2 REC 320s in series meters to the switch, but not thru the New 30amp fuse. I can meter the 72vdc In, with switch Off. But, not with switch in On position. It's apparently blocked at 30amp fuse? I've repeated it, and its confirmed, the PV voltage does not pass thru switch fuse to downstream wire to MX60, when in On position?
I'm wondering is there's a special fuse (solar?), or does the switch require a chassis ground? My Ground side, bypasses and is bussed at the combiner. 
There's a work around, but I hope not to circumvent the Safety Switch.
Anyone, familiar with this scenario?
Thank You!

BB.

Just to be clear--When you mean "Safety Switch", you are talking about over current protection such as a circuit breaker or fuse?

Typical Fuses and Circuit Breakers are just as they seem. When "on", they pass current (and voltage) across them. When "off" (or tripped), they are an "open circuit" and no current or voltage will pass through them.

Assuming these are your panels:

https://d140hlzzaoq16w.cloudfront.net/media/sparsh/product_attachment/custom/upload/REC-N-Peak-solar-panel-datasheet.pdf

The recommended series fuse/circuit breaker is 25 amps, not 30 amps.

The thing that is "special" about solar fuses/breakers/switches is that they are rated for DC Current/Voltage (and you need them to be rated, at least, for the maximum circuit voltage--Or ~80 VDC minimum in your case).

DC current is much more difficult to "stop" vs AC current... DC current sustains arcs really well, and DC breakers/fuses/switches are usually heavier duty than a similar AC version (i.e., you find that AC voltage rating is typically much higher than the DC rating for the same switch).

https://www.youtube.com/watch?v=Zez2r1RPpWY

When measuring the voltage... Where/how are you measuring? If you are measuring "across" the two terminals of the fuse//breaker, then with the switch open, you should see voltage (if the solar panels are in sunlight), and with the switch closed (turned on), you will not see any voltage... While the measurement is "valid", you may not be using the meter leads correctly(?). You want to measure the voltage across the panel + and - leads (in sunlight).

-Bill

jACKr

Aloha Bill, My Safety Switch has a single purpose. To disconnect the string 72vdc (2 series panels) completely when working at the Outback combiner. I don't really need the fuses the switch uses. The Combiner does that task. I'm likely to bridge where fuses would be. And simply use the disconnect via Switch Handle. That's all I really need. Make sense?
Mahalo, jACKr

BB.

More or less... The combiner boxes come in both Fused and Breaker (aka switching breakers)... You only need "one safety device" (over current for three or more parallel panel strings--Or one "switch" per string (aka a combiner box type) or one switch for all--Your choice). Two safety devices (such as one fuse followed by one breaker) is overkill--And can lead to confusion down the road (was it the fuse or the breaker that opened, etc.).

Having a set of "switches" (one per parallel string) is nice for debugging (i.e., is one string not working... Can switch off one at a time and see if the current goes down; working. Or if the current from the one string having low or zero amps.

Breaker based combiner box:

https://www.solar-electric.com/mnpv3.html

Touch Safe fuse hold type:

https://www.solar-electric.com/misomnsoarco3.html

Note: Do not pop the fuse holder(s) out when the unit is under power... The holders can and will arc if they are popped open under load (see YouTube video above).

-Bill