Please check my string calculations. EG4 18kpv, 60 300w panels.

[glandpuck]

This is incorrect:

MPPT 1 -25 amp limit
string 1
11 panels -
432v
511v @-35c
9.77a
string 2
11 panels -
432v
511v @-35c
9.77a
2 strings into parallel at combiner box equaling-
511v and 19.5a which is under the 600v limit, wont go over 500v mppt limit unless its record cold temps and under 25a limit.

DO NOT PARALLEL THE STRINGS FOR MPPT 1

If you do, you will double the amperage into the controller. Now, it is a 25 amp controller, if you parallel them at the combiner box, you will need a 25 -30 amp double pole breaker, 600 volts DC, you will need to increase your Dc disconnect from a 30 amp switch to a more common 60 amp capacity and same for the fuses, increase to 25 amps. The only benefit of parallel is less wire, but I would rather have the lower amps and use both MPPT inputs, A and B of MPPT 1. This is even more beneficial for future service of panels, changes, etc. Who knows, maybe in 4 years you connect a wind mill to the B side of MPPT 1.

 

[TheFlumph]

This is incorrect:

MPPT 1 -25 amp limit
string 1
11 panels -
432v
511v @-35c
9.77a
string 2
11 panels -
432v
511v @-35c
9.77a
2 strings into parallel at combiner box equaling-
511v and 19.5a which is under the 600v limit, wont go over 500v mppt limit unless its record cold temps and under 25a limit.

DO NOT PARALLEL THE STRINGS FOR MPPT 1

If you do, you will double the amperage into the controller. Now, it is a 25 amp controller, if you parallel them at the combiner box, you will need a 25 -30 amp double pole breaker, 600 volts DC, you will need to increase your Dc disconnect from a 30 amp switch to a more common 60 amp capacity and same for the fuses, increase to 25 amps. The only benefit of parallel is less wire, but I would rather have the lower amps and use both MPPT inputs, A and B of MPPT 1. This is even more beneficial for future service of panels, changes, etc. Who knows, maybe in 4 years you connect a wind mill to the B side of MPPT 1.

That’s a good point. If I end up doing three strings on mppt1 I’ll need to combine them anyway though.
But for two your way makes much more sense.

It would be cheaper to run three sets of smaller cable for mppt1 all the way to near the inverter and combine them there rather than running 6awg after combining at the array. is there a reason not to do that?

 

[FilterGuy]

Thanks, so to make it crystal clear and simple for op and I, there should be no problem with op using 12s strings, correct?

That is correct for the panels we are discussing. Two cautions

1) If the panels ever produce at full rated capacity, the MPPT will likely clip.
2) If 3 strings are put onto MPPT 1, the strings must be fused.

 

[TheFlumph]

That is correct for the panels we are discussing. Two cautions

1) If the panels ever produce at full rated capacity, the MPPT will likely clip.
2) If 3 strings are put onto MPPT 1, the strings must be fused.

Fuse or breaker correct?

If I run the separate series strings all the way inside near the inverter and combine them there, the fuses/breaker needs to be between the combiner box and inverter?
And the single series strings before the combiner are fine without breakers?

More 12awg wires are cheaper than fewer 6awg wires for me.

 

[FilterGuy]

• Either fuses or breakers are allowed for the string Over Current Protection Devices. Most (not all) combiner boxes use fuses. (If you decide to use breakers, make sure they are not directional)
• For one or two strings in parallel, OCPDs are not needed. For 3 or more strings in parallel, OCPDs are needed
• The strings are fused before they are combined.
• The breaker box can be close to the inverter or at the panels.
• To be to code, there must be an accessible disconnect. (Accessible means outside and accessible to first responders).
• The disconnect and the OCPD can not be the same device.

 

[FilterGuy]

This is incorrect:

What is incorrect?

 

[FilterGuy]

BTW: Please review this document.

EDIT: Changed link to show the correct resource

Fusing & Wire Sizing guidelines for solar panels

To get the paper, click on the orange'' button at the top of the screen. This resource is intended to help the user understand when they need to add Over Current Protection Devices (OCPDs - Fuses or Breakers) to the solar panel array and what...

diysolarforum.com

It is important to understand the current calculations for selecting fuse rating and disconnect rating.

 

[FilterGuy]

One more thing.... just to be sure we are all on the same page.

On the 18Kpv, there are 3 MPPTs and 4 inputs. Inputs 1 & 2 are internally paralleled before going to the MPPT.

 

[glandpuck]

What is incorrect?

If using MPPT 1, do not parallel the strings at the combiner box. Run 2 sets of wires directly into MPPT1 and connect the A and B terminals. As said above, this will parallel them for you. But the array must be facing in the same direction.

 

[FilterGuy]

If using MPPT 1, do not parallel the strings at the combiner box. Run 2 sets of wires directly into MPPT1 and connect the A and B terminals. As said above, this will parallel them for you. But the array must be facing in the same direction.

You can parallel either at a combiner box or in the inverter. Both are allowed. But it must be done correctly.

1) If there are two strings there is a choice.

1. Parallel the strings and connect the combined output to one or both of inputs 1 & 2.
2. Run the two strings to the inverter and connect them separately to inputs 1 & 2.

Note: OCPDs are not required, but a readily accessible disconnect is required. The disconnect can either disconnect all 4 wires before they are combined or disconnect both of the wires after they are combined (assuming they are combined outside the inverter).​

2) If there are three strings there is no choice

• The strings must be parallel outside the inverter. The combined output can go to one or both of inputs 1 & 2.
• The strings must have OCPDs
• There must be a readily accessible disconnect. The disconnect can either disconnect all 6 wires before they are combined or can disconnect both of the wires after they are combined.
• The OCPDs and the Disconnect must be separate devices.

As mentioned above, please review the document about fusing solar panels.

 

[FilterGuy]

One more note about disconnects and the 18Kpv.
The 18Kpv has built-in PV disconnects. If the unit is mounted outside in an accessible location, the integrated disconnect should be accepted by the inspectors, but not all jurisdictions do. If the unit is mounted inside, there will need to be an outside disconnect to satisfy the inspectors.

 

[FilterGuy]

All three of the following are allowable layouts as long as the arrays meet the Voc, Isc and Imp requirements.

 

[BKY2003]

Delete

 

[Quattrohead]

If the unit is mounted inside, there will need to be an outside disconnect to satisfy the inspectors.

Does the built in RSD system also satisfy this requirement if used ?

 

[BKY2003]

Deleted

 

[FilterGuy]

Between the combiner box through the disconnect and to MPPT. 8AWG wire? ISC 28.71 AMP.

The NEC requires special calculations for current on the PV array. The wires need to be sized for 1.56 X Array ISC = 1.56 X 28.71 = 44.78A

 

[FilterGuy]

Does the built in RSD system also satisfy this requirement if used ?

Unfortunately not.

 

[BKY2003]

.

 

[Quattrohead]

Unfortunately not.

I have stamped approved plans that say's it does.
EG4 18kpv, 3x Powerpro batteries and Tigo TS4-A-F/2F on the panels. Remote RSD switch installed outside.

 

[Quattrohead]

So 6awg. 4awg was a beast getting it in. Had to put the positive in the 1st slot and had to put the negative in the 4th slot negative. Thanks

If I am doing anything wrong please tell me.

Why are you using such thick cables ? 6AWG is the largest it will take, you can use 14AWG as long as the current from the panel is less than 12A and it is protected by a fuse or breaker.