Help me make sure I understand running DC high voltage wires buried in conduit back to inverter from remote (125ft) array

[hwy17]

You actually don't need to fuse or breaker a single string, since the fuse would have to be over the array's maximum current there's no point, even if it shorted the fuse wouldn't blow.

You can run each string back to the charge controller on it's own wires, instead of any paralleling.

As with voltage drop, I find this another fun way that DC solar circuits break the typical electrical rules that we are used to.

Schneider says you need DC breakers if paralleling 3 strings or more, but not for 2. I don't know how true that is. A lot of people say you need breakers for any parallel.

 

[timselectric]

Solar panels are limited by their output rating.
A single string doesn't require any OCP (Over Current Protection), because the panels are rated for the total output, even if shorted.
Two parallel strings (if the same), also don't require OCP. Because if one string gets shorted. The other string can't provide any more power than the shorted string is capable of handling.
But if you have three strings in parallel. A shorted string will now be forced to take the output of the other two strings. Which is twice as much as the shorted string can handle. And would start a fire in the shorted string.
This is why we have to individually protect three or more parallel strings.

 

[Hedges]

You last folks talk about breakers and 75c ratings and such. But for a DC HV feed to an array of panels, its not clear to me we are talking the same applications.

It would indeed seem relevant to have a DC fuse in a HV DC circuit. No one that I know of has proper DC "breakers" -- lots on eBay and amazon that get miserable reviews.

Midnight rebrands CBI breakers rated 150VDC per pole. Several ganged poles in series give you 300V, 450V, 600V.
Non-polarized is preferred in many instances, but we still see mostly polarized.

Outback has some too. Also Schneider.

I would rather have a small supply of fuses for the DC circuits. A DC circuit of known amps etc will seldom overload. You don't need to have breaker you can reset again and again. The fuse will melt with a reliable degree of accuracy to protect stuff. Inform me why the talk about a "breaker".

Agreed quality fuses are more reliable, and often have higher interrupt capability.

For PV, breaker can be a convenient disconnect. If rated for the voltage and polarity it has to interrupt.

As for Vmax and Vmin etc. I will try and find the itty bitty details pertaining to temperature. Do I really need to question the rated volts and watts that much of a PV panel? Perhaps so?? I don't really give a hoot about Vmin. I assume panel ratings are based on some arbitrary ambient temp. Say 20c/72f -- so they would actually produce LESS when hotter

Yes, hotter means lower voltage. Vmp of panel is at 25C. Panel may be at 65C, reducing voltage. You still want it over minimum MPPT. If any shadows on some panels, you want extra voltage headroom so still above minimum MPPT.

More important, Voc adjusted higher for record coldest temperature of your location must never exceed Vmax of MPPT, to avoid damage.

Under oddball conditions of extra light coming from clouds, panels can exceed rated Imp & Isc. For this reason fuses or breakers should be oversized more. Rath than just the usual 1.25x continuous current, NEC calls for 1.56x

(this is what I think I know).... And since bright sun at the proper angle is practically never going to occur, especially in cooler months, just why do I need to fuss over this detail?????

Illumination and temperature vary. So you want array to remain within MPPT limits under all conditions. Although, OK to overpanel in terms of amps and watts; MPPT will just ignore the extra on those rare occasions.