Hey Guys,

I currently have 8 545W panels connected in a 4P2S setup, this then runs into a single 6mm positive and 6mm negative solar cable via a MC4 4in1 Y connector to the inverter via the breaker box.

Question I have is, should I rather run two 6mm cables and connect 4 panels to each cable.

Just wondering if the cable may be limiting the current I am getting from the panels?

Thanks.

OMG, 4 new panels thru a single 6mm2 cable? How much amps is that - 60A?

MC4 connector are rated for 30A. Are they hot and melting already or still nice and cool?

Based on the length of cable, there will be some voltage drop. For example, 60Amps over 20m of 6mm2 cable loop is a drop of almost 4Volts. That is 240W of loss which goes in the heat.

By rewiring you can make a bit more energy, but only during peak hours. In the low-light (low amps) the yield will be the same. But the most important would be safety improvement.

BTW: there should be DC fuses whenever you parallel more than 2 strings together. Amp rating of the fuse should be higher than Isc, but lower than 2x Isc. Reason is: if one of the paralleled strings will be shorted, other 3 strings will start pushing Isc into it....and this might start a fire. With the proper fuses, the fuse will blow immediatelly.

My question? What Scc or inverter are you using to accommodate 2S4P dc input current? The 545w JA solar panel has a ISC of 13.93A and IMP of 13.04A that equate to 55.72A and 52.16A respectively. As mentioned on previous post from @Youda with that much current there is safety concerns.

Each solar panel should have a series fuse. Below some guidance for safely wiring of solar arrays.

Hey @TaliaB and @Youda ,

Thank you for the replies.

On that information, I have reconfigured the system.

See attached wiring diagram.

Thanks.

This is better, but IMHO there's still a couple of space for improvements:

• Those 25A fuses might blow from time to time, since you have 26A (2x 13.9A) on each fuse.

• Each series of panels should have it's own fuse. AFAIK, paralleling two strings and then fusing both of them together, and then paralleling all of this again is not a recommended solution.

Looking at components you have, I would suggest rewiring like this:

String1

• 2 panels i series

• 1x 20A fuse
  

String2

• 2 panels i series

• 1x 20A fuse

String3

• 2 panels i series

• 1x 20A fuse

String4

• 2 panels i series

• 1x 20A fuse

Combine string1+string2 in parallel, go thru 2-pole disconnect A.

Combine string3+string4 in parallel, go thru 2-pole disconnect B.

Combine outputs from disconnect A + disconnect B in parallel, put into Surge Arrestor.

Connect output from Surge Arrestor directly to the inverter MPPT input (no need for disconnect between the Surge Arrestor and MPPT input).

But let's wait what more experienced engineers will say....

Edited July 8, 20251 yr by Youda

Thank you Youda, lets see what others have to say and take it from there.

2 hours ago, Youda said:

This is better, but IMHO there's still a couple of space for improvements:

• Those 25A fuses might blow from time to time, since you have 26A (2x 13.9A) on each fuse.

• Each series of panels should have it's own fuse. AFAIK, paralleling two strings and then fusing both of them together, and then paralleling all of this again is not a recommended solution.

Looking at components you have, I would suggest rewiring like this:

String1

• 2 panels i series

• 1x 20A fuse
  

String2

• 2 panels i series

• 1x 20A fuse

String3

• 2 panels i series

• 1x 20A fuse

String4

• 2 panels i series

• 1x 20A fuse

Combine string1+string2 in parallel, go thru 2-pole disconnect A.

Combine string3+string4 in parallel, go thru 2-pole disconnect B.

Combine outputs from disconnect A + disconnect B in parallel, put into Surge Arrestor.

Connect output from Surge Arrestor directly to the inverter MPPT input (no need for disconnect between the Surge Arrestor and MPPT input).

But let's wait what more experienced engineers will say....

Your suggested rewire is solid. Each string is fused independently, so no risk of excessive backfeed.

Two levels of combination allow better fault isolation and easier maintenance.

Disconnects between parallel strings are essential for safe serviceability.

Hmmm, but that would mean I would need to run 6mm for each string before paralleling them in the box.

A fair amount more to spend in on cable In that case.

Normally, they use "pv combiner box" for this. Located near the panels, loaded with fuses. It combines the strings, allowing you to run just one pair of thick cables plus grounding to run further down.

Has pros but cons too...

Example:

Another option, when fusing only the positive pole of each series, is to connect negative poles and run just one negative wire further down.

For your case, it would be 4 separate positive wires + 2 negative wires.

So, ideally, my wiring should look similar to this?

Wouldn't running two strings into 1 neg have the same effect of running my old setup? i.e. too many amps through the cable?

This will work OK.

It will be 28Amps at Isc, which is okay for 6mm2. (I can calculate voltage drop and power drop at various loads, if you want to know)

If you could, that would be greatly appreciated.

Or let me know what the formula is and I can do it myself.

28A going thru 20m loop of 6mm2 copper cable will create voltage drop of 1.7V and power loss of 47W.

At 14A load, outside the peak-hours, its 24W.

So the power loss will be less than 100W for all your panels combined....and only during peak hours.

Will work ok, you will not even notice.

BTW: Use ElectroDoc Pro mobile phone app for the calculations. It has all the resistance tables for various metals built-in, together with proper formulas.

Edited July 9, 20251 yr by Youda