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Help picking right lightning protection, fuses, and breakers for each of four strings

RevMikeB

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Feb 27, 2022
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So, as many of you know, I'm running 3 strings from the house and 1 string from an extended garage that will each carry a lot of DC current. All four strings will be running separately with 8AWG right up close to the inverter. I'd like to install a box next to the inverter with 4 inputs for the strings and each of them to have their own outputs (4 total) to run to the inverter. I will have two insulated green ground wire running to the box also, one from the roof top of the house connected to the rails and one from the roof top of the garage, likewise connected to the rails. I'd like each string to have its own dedicated breaker, fuse, and lightning protection in the box before each of the four strings are separately run into to the inverter. Each string will be caring the DC current a little under the inverter specs:
  • Max. Input Power per MPPT [W]: 5700
  • Max. Input Voltage per MPPT [V]: 600
  • Max. Input Current per MPPT [A]: 13.5
Can anyone please give me an idea what I need to purchase to put into the box (links appreciated)?? Most every combiner box is made to combine strings together to have less outputs than inputs, which is NOT what I want to do. I want to keep them separate while getting the protection from fuses and breakers. Any help would be appreciated. The inverter has its own built in DC disconnect, so that is NOT needed.
 
So, as many of you know, I'm running 3 strings from the house and 1 string from an extended garage that will each carry a lot of DC current. All four strings will be running separately with 8AWG right up close to the inverter. I'd like to install a box next to the inverter with 4 inputs for the strings and each of them to have their own outputs (4 total) to run to the inverter. I will have two insulated green ground wire running to the box also, one from the roof top of the house connected to the rails and one from the roof top of the garage, likewise connected to the rails. I'd like each string to have its own dedicated breaker, fuse, and lightning protection in the box before each of the four strings are separately run into to the inverter. Each string will be caring the DC current a little under the inverter specs:
  • Max. Input Power per MPPT [W]: 5700
  • Max. Input Voltage per MPPT [V]: 600
  • Max. Input Current per MPPT [A]: 13.5
Can anyone please give me an idea what I need to purchase to put into the box (links appreciated)?? Most every combiner box is made to combine strings together to have less outputs than inputs, which is NOT what I want to do. I want to keep them separate while getting the protection from fuses and breakers. Any help would be appreciated. The inverter has its own built in DC disconnect, so that is NOT needed.
I'm in the process of redoing my entire system.
This is how I am building my solar control box. It will be located directly above my inverter. (With room for future expansion) links will follow.
 

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Links for what I bought.
Voltage Surge Arrester Device, 2P Surge Protective Device DC Photovoltaic Lightning Protector Low-Voltage Arrester 3.0KV (2P40KA) https://www.amazon.com/dp/B07PFVQBL2/ref=cm_sw_r_cp_apan_i_PSHBK08B0CC08WZ1KKZ8?_encoding=UTF8&psc=1

DC Miniature Circuit Breaker, 2 Pole 1000V 25 Amp Isolator for Solar PV System, Thermal Magnetic Trip, DIN Rail Mount, Chtaixi DC Disconnect Switch C25 https://www.amazon.com/dp/B09BQR289J/ref=cm_sw_r_cp_apan_i_39GAW7NBY7ABSRF206NW?psc=1

smseace Circuit Breaker Box Distribution Protection Box, ABS Plastic Transparent Cover Waterproof Distribution Box IP65, for Indoor Wall Circuit Breaker (18 Way ) https://www.amazon.com/dp/B09G338V82/ref=cm_sw_r_cp_apan_i_SRGG4107GM9C4H5BYNKX
 
I'm in the process of redoing my entire system.
This is how I am building my solar control box. It will be located directly above my inverter. (With room for future expansion) links will follow.
That looks good. Can that box be mounted outside, or is that for inside only? I like the look of it.
Links for what I bought.
Voltage Surge Arrester Device, 2P Surge Protective Device DC Photovoltaic Lightning Protector Low-Voltage Arrester 3.0KV (2P40KA) https://www.amazon.com/dp/B07PFVQBL2/ref=cm_sw_r_cp_apan_i_PSHBK08B0CC08WZ1KKZ8?_encoding=UTF8&psc=1

DC Miniature Circuit Breaker, 2 Pole 1000V 25 Amp Isolator for Solar PV System, Thermal Magnetic Trip, DIN Rail Mount, Chtaixi DC Disconnect Switch C25 https://www.amazon.com/dp/B09BQR289J/ref=cm_sw_r_cp_apan_i_39GAW7NBY7ABSRF206NW?psc=1

smseace Circuit Breaker Box Distribution Protection Box, ABS Plastic Transparent Cover Waterproof Distribution Box IP65, for Indoor Wall Circuit Breaker (18 Way ) https://www.amazon.com/dp/B09G338V82/ref=cm_sw_r_cp_apan_i_SRGG4107GM9C4H5BYNKX
It looks like all of that would work for me, if I'm not correct, please say. However, the box doesn't look rated for outside, which is what I'd like. Do the surge protectors have fuses in them?
 
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That looks good. Can that box be mounted outside, or is that for inside only? I like the look of it.

I thought that the breaker for DC was ONLY supposed cover one side (positive) and not the negative. Am I wrong about that? Is a dual breaker ok?
You can go either way. I prefer to disconnect both wires. And, the NEC requires it. If the solar is not a grounded system. (As in the negative side is bonded to ground) some inverters bond the negative, but that's after my disconnect. So, I prefer to disconnect both.

Edit: yes, that box is weather proof.
 
PS: I just realized that I hastily snapped in the wrong breakers for that picture. Those are AC breakers, for my grid power box. The DC breakers I linked to, will be the ones installed when used.
 
PS: I just realized that I hastily snapped in the wrong breakers for that picture. Those are AC breakers, for my grid power box. The DC breakers I linked to, will be the ones installed when used.
I think I'd need/go with a metal box for outside with some kind of grounding bar inside.
 
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This is another one I am using. It comes with a ground bar installed.

QILIPSU IP65 Clear Cover 12 Way Power Distribution Box with Bus Bars and DIN Rail for Miniature Circuit Breaker, PC Plastic (12 Way) https://www.amazon.com/dp/B08HCXHDC9/ref=cm_sw_r_cp_apan_i_V102NF4TDZFNRBTEAQR1?psc=1
Ok, so I'd need four of those DC breakers and four surge protectors. To wire, I bring the first string from the PV (+ & -) into the top of the breaker. The + & - are run out of the bottom of the breaker directly to line 1 (+ & -) DC input in the inverter. The surge protector is installed directly next to the breaker. I run a second thicker 6-gauge red wire and a second thicker 6-gauge black wire out of the bottom of the breaker from both + & - and loop it around to the top of the + & - of the surge protector. Out of the bottom of the surge protector, I run a thick green/yellow wire to the ground bar. Does this all sound correct, since the inverter has its own integrated DC shut off switch? I will do the same for each of the four strings to keep them independent of one another, since I want to keep everything in series and don't want anything run in parallel to double the current, which would overload the inverter. Since the four breakers and four surge protectors are dual, will they all fit in the box of the link above? I heard that the breakers have to have built in over charge protection in them for the surge protectors to work, so it appears that is the case if I'm reading it correctly, and they are not simply disconnects.
 
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My big question is if 1000V breakers and surge protectors for each string are too much given that each string is NOT supposed to be more than the following:
  • Max. Input Power per MPPT [W]: 5700
  • Max. Input Voltage per MPPT [V]: 600
  • Max. Input Current per MPPT [A]: 13.5
 
I would connect the surge protectors to the tops/inputs of the breakers. This way, they are also protecting the breakers. This also simplifies the wiring. Install them in sets. (Breaker #1 then suppressor #1, then breaker #2 then suppressor #2, and so on) 4 breakers and 4 suppressors will require 16 spaces in the panel box.
You'll need this one.

QILIPSU IP65 Clear Cover 18 Way Power Distribution Box with Bus Bars and DIN Rail for Miniature Circuit Breaker, PC Plastic (18 Way) https://www.amazon.com/dp/B09HXLRVTN/ref=cm_sw_r_cp_apan_i_Q8PJ492RW778SJ8R3D39?psc=1
 
My big question is if 1000V breakers and surge protectors for each string are too much given that each string is NOT supposed to be more than the following:
  • Max. Input Power per MPPT [W]: 5700
  • Max. Input Voltage per MPPT [V]: 600
  • Max. Input Current per MPPT [A]: 13.5
The 25 amp breakers that I linked are fine for these circuits. You could step down to 20 amp, if you wanted to. 15 amp would be to small. Since OCP should be sized for 125% of the expected load.
13.5 x 1.25 = 16.875
 
Wouldn't this one be better, since its 600Volts?

The 25 amp breakers that I linked are fine for these circuits. You could step down to 20 amp, if you wanted to. 15 amp would be to small. Since OCP should be sized for 125% of the expected load.
13.5 x 1.25 = 16.875
So the amps are more important consideration than the volts?
 
The panels have 8.97 max current in Amps, and I will be running all strings in series. The inverter max is 13.5A per string
 
No, I'm running all strings in series. The volts will be between 500l-600 volts per string. Amps will be 9 amps per string.
I think that you mean parallel.
In series, the voltage adds up.
I'm obviously new at this, so forgive my ignorance, but if each string has under 600 volts or 9 amps, it sounds like a 1000V breaker on each string is too much, unless it is the amp rating that I should focus upon.
 
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