Am I required to use a fused/breaker combiner box and where can I put it?

[RevMikeB]

I'm running 3 DC strings from the house roof and 1 DC string from the exterior garage to the inverter at ground level. I cannot combine any of the strings because the Amps exceed specs. So, my question is whether or not I need and am required to run my strings into some kind of fused/breaker box before going into the inverter? And since I cannot combine strings, why would the box have to go on the roof? Couldn't it go next to the inverter at ground level or is that not allowed?

Also, I'm going to be grounding the rails with #6 bare copper wire that will run to its own grounding rod. (All panels will then be grounded due to the web fasteners.) Would it be ok to attach a green braded grounding wire to that copper wire on the roof and run it in the same metal conduit to the inverter, grounding the case and grounding bar? Is it wrong to run a bare wire with the DC cables in metal conduit to the inverter?

 

[RevMikeB]

So, why is the maximum output of watts exactly half of what the maximum input of watts is on the inverter specs?

 

[MisterSandals]

I cannot combine any of the strings because the Amps exceed specs.

How about explaining your panels (watts, Voc), SCC (max input volts) and overall situation to see if there is a way to make this work?

 

[timselectric]

Since I only see two general questions. I will just answer them , generally.
You can locate a combiner box, anywhere it's convenient.
A bare ground wire in a conduit with DC wiring, is completely acceptable.

Edit: oops, I missed the main question.
No, a combiner box is not a requirement. It's a convenience.

 

[RevMikeB]

Since I only see two general questions. I will just answer them , generally.
You can locate a combiner box, anywhere it's convenient.
A bare ground wire in a conduit with DC wiring, is completely acceptable.

Edit: oops, I missed the main question.
No, a combiner box is not a requirement. It's a convenience.

But does the combiner box provide an extra level of security? Or would an inline fuse do the same and much cheaper at that????

 

[MisterSandals]

But does the combiner box provide an extra level of security? Or would an inline fuse do the same and much cheaper at that????

I really have no idea what you are trying to do.

A combiner box performs a different function than an inline fuse.

 

[timselectric]

But does the combiner box provide an extra level of security? Or would an inline fuse do the same and much cheaper at that????

I only use inline fuses. Not wasting money on a combiner box.

 

[RevMikeB]

How about explaining your panels (watts, Voc), SCC (max input volts) and overall situation to see if there is a way to make this work?

On grid system, 335W per panel, 13-16 panels per string, 4 strings, 9 amps each panel, the max amp input per string is 13.5A. Since I am running DC current from roof to inverter, I just wanted to know if some kind of combiner box with breakers or fuses would be required by the electric company/building inspector for an ON GRID system? And if it were required for the breakers or fuses, I was wondering why one would put it on the roof in a location that is hard to get to if I wasn't going to be combining strings?

 

[MisterSandals]

the max amp input per string is 13.5

This seems unusually low. What SCC do you have?

Any SCC that takes what sounds like hundreds of volts, i would think, handle more than 13.5A.


335W / 9A = 37.2V
37.2V x 16 = 595V

If you have a 600V max input SCC, then you better take into account any temperature compensations for voltage should the panels be in weather below where they are rated, 25C (77F).

 

[RevMikeB]

This seems unusually low. What SCC do you have?

Any SCC that takes what sounds like hundreds of volts, i would think, handle more than 13.5A.


335W / 9A = 37.2V
37.2V x 16 = 595V

If you have a 600V max input SCC, then you better take into account any temperature compensations for voltage should the panels be in weather below where they are rated, 25C (77F).

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[RevMikeB]

This seems unusually low. What SCC do you have?

Any SCC that takes what sounds like hundreds of volts, i would think, handle more than 13.5A.


335W / 9A = 37.2V
37.2V x 16 = 595V

If you have a 600V max input SCC, then you better take into account any temperature compensations for voltage should the panels be in weather below where they are rated, 25C (77F).

I live in central North Carolina. How do I know what temperature compensations to use? Besides, if I push the envelope, I will find out faster than anyone when there is a solar flare!!! BRHAHAHAHA I'm going to use the max 8 AWG wire for DC input and 6 AWG wire for AC output, so at least the wire should handle things. 65 foot runs with wire at most.

 

[MisterSandals]

I live in central North Carolina. How do I know what temperature compensations to use?

People generally use the record low for your area.
It looks like the MPPT (optimised) range is only to 550V so I would shoot for just below that.

Assuming 37.2 is Voc… (not Vmp)
550 / 37.2V = 14.78 panels
I would strongly consider a max of 14 in series (based on 37.2 being Voc)

 

[timselectric]

I agree, stay well below the 600v.
That's boom boom Voltage.
14 panels is a perfect fit.

 

[MisterSandals]

Let’s run some temp compensation numbers for 0 deg C (32F)
Guessing your panel temp coefficient is .35%


37.2V x .0035 x 25 deg drop = 3.255V gain per panel

(37.2V + 3.255V) x 14 panels = 566V.

REALLY need to use Voc for these calcs.

 

[RevMikeB]

People generally use the record low for your area.
It looks like the MPPT (optimised) range is only to 550V so I would shoot for just below that.

Assuming 37.2 is Voc… (not Vmp)
550 / 37.2V = 14.78 panels
I would strongly consider a max of 14 in series (based on 37.2 being Voc)

46.81 VOC per panel

 

[MisterSandals]

46.81 VOC per panel

BIG difference!

Let me redo the numbers…

 

[RevMikeB]

I agree, stay well below the 600v.
That's boom boom Voltage.
14 panels is a perfect fit.

So, you think 13 panels on one string, 14 panels on another, 14 panels on a third, and 16 panels on the last string would be too much?

 

[timselectric]

Pre-emptive ouch.

 

[timselectric]

It's looking more like 11 or 12 panels. With that VOC and temperature compensation.

 

[MisterSandals]

So, you think 13 panels on one string, 14 panels on another, 14 panels on a third, and 16 panels on the last string would be too much?

Since we are cutting it close, what is the lowest temp you want your SCC to handle? (As in survive)