Wire Size from panels to SCC?

[offroad]

Just finished mounting a pair of 395w panels to the roof of my RV, and want to make sure I get the wiring correct to the SCC.
Panels will be wired in parallel to a Victron 100/50 SCC.

49.5 Voc
41.4 Vmp
10.23 Isc
9.55 Imp
Max Series Fuse 20A

Planning on using wire sizes below.
Panels have 5ft 12ga leads, then 6ft to combiner box - 10ga.
Combiner box to breakers then SCC about 15ft - 8ga.
SCC to breakers then main battery bus bars about 5ft - 6ga.

Will be using DC breakers just before and just after the SCC (basement storage), both are 500v 32a coming into SCC, and 63a coming out.
With the breakers do I still need a fuse for each panel on the roof, and if so should the fuses be 20a?

My DC bus bar negative is grounded to the frame of the RV is that enough for panel ground, or should I have a third wire attached to the frame of the panels and if so what size?
Can I use a short wire from the panels to the combiner box ground connection?

Thanks for all advice

 

[HRTKD]

On an RV, most solar panels are not grounded to the frame. Right or wrong, that's how most of them are.

A fuse is not necessary between the two panels since it's only two panels. If it was three, you would need a fuse.

Given the voltage, amperage and lengths you provided, your wire size is well within acceptable limits. Probably around 1% to 1.2% voltage drop, not taking into account the connections.

A combiner box isn't necessary. You could simply use a Y cable with MC4 connectors on it.

 

[offroad]

A fuse is not necessary between the two panels since it's only two panels. If it was three, you would need a fuse.

A combiner box isn't necessary. You could simply use a Y cable with MC4 connectors on it.

Thanks for the tip on the Y cable, that will be easier.

Can you expand on why a fuse isn't needed for two panels but would be for three?
With a 32a DC breaker on the input side to the SCC (due to the 8ga wire), I'm concerned about 12ga wires on the roof having issues before the breaker trips.

 

[HRTKD]

Each panel is rated for a certain amount of amperage. The feedback from one panel to another won't exceed that. But if you have two panels with issues, their feedback into a third panel would exceed the limit. At least that's my understanding. It's not the greatest explanation, sorry.

Your 12 gauge wires occur before the two panels are combined into a parallel configuration. There is double the amps after the Y connection, so the wire after the Y connection needs to be able to handle that doubling.

Note that we recommend a dual pole breaker upstream of the solar charge controller. You want to break both sides of the circuit. A single pole breaker downstream of the solar charge controller on the positive side is acceptable.

 

[HighTechLab]

Solar panels in a short-circuit condition are a limited current source - limited to the ISC (short circuit current rating).

Most solar panels have 12AWG wire for their MC4 connectors. 12AWG in this scenario has an ampacity of 20 amps. Most solar panels have a short circuit current of around 8-9A. Two panels driving a short only run 16-18A which is within the rating of the wire so no fire. Three panels in parallel increases the short circuit current to 24-26A, which exceeds the current rating of the wire, likely leading to a fire. Adding a fuse properly sized for the wire stops the flow of short-circuit currents above the rating of the wire.

 

[offroad]

Solar panels in a short-circuit condition are a limited current source - limited to the ISC (short circuit current rating).

Most solar panels have 12AWG wire for their MC4 connectors. 12AWG in this scenario has an ampacity of 20 amps. Most solar panels have a short circuit current of around 8-9A. Two panels driving a short only run 16-18A which is within the rating of the wire so no fire. Three panels in parallel increases the short circuit current to 24-26A, which exceeds the current rating of the wire, likely leading to a fire. Adding a fuse properly sized for the wire stops the flow of short-circuit currents above the rating of the wire.

I have two large panels with an ISC of 10.23a each (2x in parallel = 20.46a) and on the sticker the max fuse rating is 20a.
They have 12ga leads, would you recommend a 20a fuse on each panel?

 

[HighTechLab]

I have two large panels with an ISC of 10.23a each (2x in parallel = 20.46a) and on the sticker the max fuse rating is 20a.
They have 12ga leads, would you recommend a 20a fuse on each panel?

Technically, yes...but being this close I wouldn't worry about it. If you were to fuse I would put a 15a per panel. Since you are so close to the max voltage of the controller, you can't go to a series configuration.