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MC4 connectors rated for 30a.... but my planned 2s4p is 33.08a? Problem?

IvoryO

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Joined
Mar 24, 2022
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So I'm planning on doing 2s4p of the SanTan 250w panels.
  • Rated Power: 250W
  • Open circuit voltage (VOC): 37.6 V
  • Max power voltage (VMP): 30.3 V
  • Short circuit current (ISC): 8.85 A
  • Max power current: 8.27 A
I'm getting 10 AWG cable, and getting the 1 to 4 solar branch, where I'll combine near the panels and run a single wire to my PIP LV2424 MSD MPPT ( https://watts247.com/product/pip-lv2424-msd/ ) all in one inverter (where they are wired with solar attachments for plugging in, as Will does in his videos.

BUT, the problem is.... it looks like 4p of 8.27a is going to give me 33.08a .... and the MC4 connectors are only rated for 30a.....

Does this mess up all my plans? And now I'll need a combiner box and more complicated system? Along with redoing the connection into the MPPT?

This is my first solar setup, so still trying to navigate it all.... but it seems like it's too much amps for a simple setup?
 
The combined Isc will be 35.4A so you are over the 30A limit even more.

A combiner box is a place to fuse each string (which you need to do) and it eliminates all of the MC4 connectors allowing for whatever amperage you need.

None of this affects the connection to the MPPT. You still run a single pair of wires from the combiner to the PV input of the MPPT.

I've seen reference to 4-to-1 branch connectors that can handle more than 30A. There's no problem with the connections from each string, just the final single pair output which is the only connection that is over 30A. If the connectors for that final pair into the 4-to-1 connector can handle 36A or more then you may not need a combiner box. But don't forget you still need to fuse each parallel string. Inline MC4 fuse connectors can be used for that.

One other option to consider - get a 9th panel and do 3S3P. The Voc is still well below 145V, even down to -40ºC/F and the Isc is only 26.55A. You'll have no trouble with 2250W of solar panels with the 80A SCC.
 
10AWG is only rated for 30 amps, so 33amps could be a fire hazard. I wouldn't try it.

I typically derate wires by 80%. So if using 10AWG, I wouldn't try to push 30 amps continuous, only about 20-24 amps. I also derate it even more if I'm pushing it through conduit.

I suggest #8 or #6AWG THWN from your combiner box all the way into the LV2424 buried in conduit. (You should verify first that it can take a #8 or #6 wire input). This way you should be able to handle close to 50Amps if you need it in the future. For 80amps continuous you'd need something like #3, which is pretty beefy.
 
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10AWG is only rated for 30 amps, so 33amps could be a fire hazard.
10AWG pure copper wire can easily handle 60A or more. But depending on the voltage and wire length, much over 30A can result in too much voltage drop. To be clear, I'm not saying you should push 60A through 10AWG wire. But 10AWG can be fused up to 60A. 33A through 10AWG will not be a fire hazard but you definitely need to consider voltage drop. But in this case we are talking about a Vmp of 60.6V so voltage drop at 33A will be very minimal if the length is under 20 feet (roughly).
 
One other option to consider - get a 9th panel and do 3S3P. The Voc is still well below 145V, even down to -40ºC/F and the Isc is only 26.55A. You'll have no trouble with 2250W of solar panels with the 80A SCC.

That seems like the easiest solution. Then I can go ahead with the typical 10 AWG and mc4 connectors.

BUT, I think trying to order a single used panel would be crazy high shipping. So would I be able to use just any random 250w panel instead to add onto the others?
 
Thanks for the help.

Is it absolutely critical that a 9th panel is there? Or could I do 2 sets of 3.... and then 1 of 2?
All strings should be equal voltage and amperage for it to work well. Trying to do 3 mismatched strings in parallel won't give good results. You'd basically end up with similar results to doing 2S3P (6 panels). Though 2S3P is a viable option. But it is 500W less than your originally planned array.
 
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