MC4 cable size

[swbrains]

As part of my research for setting up a simple solar panel (just a single 100W panel to (re)charge a single AGM battery), I have been doing lots of calculations online for the size of the wire needed between the panel and the charge controller/battery. In my case, I will be forced to have the panel on the back of the house, but the battery and charge controller would be in my garage at the front, at least 75-85 "cable" feet away accounting for vertical wire travel and some slack in the attic.

After using some online calculators to determine wire sizes, I always seem to come up with needing some very large wire sizes -- around 6 AWG to 4 AWG -- depending on how much voltage loss I want to tolerate. If I played with slightly higher losses and the shortest possible cable length, I could get it to produce an 8 AWG cable size requirement, but no calculator produced a 10 AWG cable size for these parameters.

So while doing some online research, I came across a couple of companies selling various solar components (panels, controllers, and cables, etc.). A couple of them had MC4 extension cables like this one: https://www.civicsolar.com/product/m...-pv-wire-150ft

I'm confused by this. Why would a company make/sell a 10 AWG cable with MC4 connectors (so it theoretically was designed to be used as one long length) to be connected to a solar panel if the voltage losses over 75 to 85 feet seem to demand #6 or #4 wire to keep the losses at an acceptable level? I'm sure I'm not understanding something about wire sizes used to connect a panel to the controller, but this confused me based on what I've been seeing in various wire size calculators.

Thanks for any clarification anyone can provide.

[sensij]

Typically, long MC4 extension cables could be used when several panels are wired in series, raising the circuit voltage to a high enough level that the voltage drop is small. In other words, the same 0.5 V drop is a big deal on a 12 V circuit, not a big deal on a 48 V circuit. The heavier wire requirement you are running into is a consequence of using a 12 V panel (17 Vmp, or perhaps 15 V on a PWM controller) as opposed to a larger 20 V (60 cell, 29 Vmp) or 24 V (72 cell, 35 Vmp) panel.

[bcroe]

I'm confused by this. Why would a company make/sell a 10 AWG cable with MC4 connectors (so it theoretically was designed to be used as one long length) to be connected to a solar panel if the voltage losses over 75 to 85 feet seem to demand #6 or #4 wire to keep the losses at an acceptable level? I'm sure I'm not understanding something about wire sizes used to connect a panel to the controller, but this confused me based on what I've been seeing in various wire size calculators.

If a pair of those extensions caused a loss of 4V, it would be a big hit to a 12V system. But I have similar
wire runs out to strings of 12 series panels, running at 400V. My system can afford that 1% lose, that might
be 33% for you. Bruce Roe

[swbrains]

Ah, now it makes sense. I was totally not thinking about a higher voltage with multiple panels. Thanks!

[frankiek3]

They are also cut in roughly half with so the ends with female and male MC4 connectors go to the panel.