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Is this 16A PV disconnect a fire hazard?

kolek

kolek

Inventor of the Electron
Joined
Sep 29, 2021
Messages
510
I've already purchased SMSEACE FCY8-63 (16A, 2P, 500V) breaker/disconnects for our PV array.
Explorist solar youtuber says you should buy at least 30A PV disconnects:

Makes me concerned that the 16A rating on these disconnects is too low.

My solar panels are:
LONGI SOLAR HALF-CUT LR4-72HPH-455M, (455W) MODULES - each string will be 7 panels in series

Do I need 30A+ PV disconnects?
 
That video is misleading, he is mixing disconnects and breakers.
You protect the wire size or device with the appropriate fuse/breaker.
A single string of panels do not need this protection but it is good to have anyway.
Your 500v 16a breaker will be fine.
 
Just so I understand, when connecting in series, you take the ISC of the panel, which in this case is 11.66A and you need a breaker that exceeds that?

And if I was doing, say, 4 panels in parallel, I would need a breaker bigger than 4 x 11.66 = 46.64A ?
 
kolek said:
@Quattrohead Ok great thank you.
I think this was the concern:
Click to expand...
This is when wired incorrectly. Most DC breakers for PV use are polarized, meaning that the direction of power flow matters.
So you need to connect them properly (notice the +/- signs, and INPUT / LOAD markings).
 
kolek said:
Just so I understand, when connecting in series, you take the ISC of the panel, which in this case is 11.66A and you need a breaker that exceeds that?

And if I was doing, say, 4 panels in parallel, I would need a breaker bigger than 4 x 11.66 = 46.64A ?
Click to expand...
Yes
 
meetyg said:
Yes
Click to expand...
So @meetyg wouldn't you agree that there should be a bigger buffer than just 14A - 11.66A = 2.34A?
Especially given that these are made in China junk breakers to begin with.
 
Last edited:
meetyg said:
This is when wired incorrectly. Most DC breakers for PV use are polarized, meaning that the direction of power flow matters.
So you need to connect them properly (notice the +/- signs, and INPUT / LOAD markings).
Click to expand...
No i think the example I linked to should take you to the middle of the video, that shows a case where the input amperage is 4X the rating of the breaker and it burns up even tho its polarity is set correctly.
 
Last edited:
Isn’t this why each PV string has a fuse? I like DC breakers for convenience but don’t trust them.
 
Anyone? Don't you need a greater buffer on DC disconnects?
 
Last edited:
Brett V said:
If you’re going to quote me in a post for a response and then edit the post, don’t expect any more help. Do whatever you want, good luck.
Click to expand...
I don't want to derail my own thread starting a discussion on a different topic. Sorry I edited my post. Sorry if you were offended, I meant no offense. I don't want to start adding fuses to my strings, I just want to address this breaker issue by itself. Sorry if you feel that is misguided.
 
MrThisIsME said:
Would never take this guys word as gospel. No real background and in it for the glam / money.
I use to subscribe to him but noticed he deletes comments / discussions that correct his errors.
Not someone to trust in my eyes.
Click to expand...
Right but it makes sense that you'd want 30-50% or more extra ampacity of your disconnects to your panel ISC when connecting in series. Logically, and that's unrelated to the youtube video. No? Feel free to correct me, I'm no expert.
 
Sizing to ISC is invalid. As previously mentioned (and with very few exceptions) breakers and fuses are meant to protect cables, nothing else, and thus sized accordingly to the cable capacity (by voltage, amp, temp, even voltage drop). You can always put a lower amperage breaker / fuse then the cable can sustain, never higher.
 
@MrThisIsME or anyone else that wants to answer.
EXPLORIST (the youtuber) claims that PV breakers are meant to act as disconnects only, not to add protection. Is this correct?
 
kolek said:
@MrThisIsME or anyone else that wants to answer.
EXPLORIST (the youtuber) claims that PV breakers are meant to act as disconnects only, not to add protection. Is this correct?
Click to expand...
Darn! Now you made me watch the video. Not sure what his thought process is for such, but makes no sense to me. Maybe that was the only DC breaker he had??? Or a sponsored video.

So now he built a system with no over-current or blocking in place. What now? Build another box with the correct size breakers or fuses?

Are you aware that you can buy these Chinese boxes off Amazon premade cheaper then he is building here.
 
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