Acceptable wire for solar install

[rubiks1]

Hello everyone
I tried a search but could not locate the answer to my question. Here is the scenario. 24 volt system , I am going to have 14 panels wired in 7 strings of 2 (ISC is 8.21) to a combiner box in breakers etc which gives me a total of 57.47 amps. From there they will be combined onto a 4 ga wire coming down into the charge controller. This is the wire that I am concerned about. Can this be THHN, THHN2 or TWN? Or is there another type of wire that will pass code.

Thanks!

[Sunking]

There are a few you can use but it completely depends on how the wire is used. As of now from your list THHN-2 appears to be the only one you could use. Read this document for a full list and match Insulation type for its use. You selection is based on:

• Temperature. You want 90 degree. That Eliminates THWN, THW, RHW USE, and SE
• Moisture Wet Locations.
• Conduit Raceway
• Sunlight

I will give you a hint. You want anything with -2 which will give you 4 cable types to select from. Now go figure out what -2 means.

[Mike90250]

take the expected cost of your 24V wire, and compare it to the cost of an MPPT controller, and running 3x the voltage (and 1/3 the amps) and see if you save any money with smaller combiner box, fewer breakers (but they are higher voltage) and smaller wires & conduit.

And be sure you are running at least 30Vmaxpower into your PWM controller so it can feed 28V to your batteries on a hot day for a full charge. Be sure your panels are not 26V and you think they will charge a 24v battery, you need more voltage to push power into a battery, than the voltage you take out.

[rubiks1]

Thanks Sunking. HMM what does -2 mean? 90c and wet

There are a few you can use but it completely depends on how the wire is used. As of now from your list THHN-2 appears to be the only one you could use. Read this document for a full list and match Insulation type for its use. You selection is based on:

• Temperature. You want 90 degree. That Eliminates THWN, THW, RHW USE, and SE
• Moisture Wet Locations.
• Conduit Raceway
• Sunlight

I will give you a hint. You want anything with -2 which will give you 4 cable types to select from. Now go figure out what -2 means.

[rubiks1]

Mike90250

I will be running a mppt controller most likely a classic 150 but the jury is not out yet as I am still doing research on that one. Open circuit on these panels are 32.9 and they will be wired in strings of 2 otherwise I will have to buy another panel to make 15
Thanks for all of the help!

take the expected cost of your 24V wire, and compare it to the cost of an MPPT controller, and running 3x the voltage (and 1/3 the amps) and see if you save any money with smaller combiner box, fewer breakers (but they are higher voltage) and smaller wires & conduit.

And be sure you are running at least 30Vmaxpower into your PWM controller so it can feed 28V to your batteries on a hot day for a full charge. Be sure your panels are not 26V and you think they will charge a 24v battery, you need more voltage to push power into a battery, than the voltage you take out.

[Sunking]

Mike90250

I will be running a mppt controller most likely a classic 150 but the jury is not out yet as I am still doing research on that one. Open circuit on these panels are 32.9 and they will be wired in strings of 2 otherwise

Maybe, Maybe not. That will depend on your location and battery voltage.

For example if you live in an area with mild winter temps and a 48 volt battery you can have as many as 4 panels in series. 14 panels is a bit of a restrictive number only leaving you one option. 12, 15, and 16 have a couple of options.

[rubiks1]

Sunking

I am in San Jose CA and the battery bank is 24 volts. On the 15 panels piece I have been considering adding a 15th panel to the array.

Thanks again

Maybe, Maybe not. That will depend on your location and battery voltage.

For example if you live in an area with mild winter temps and a 48 volt battery you can have as many as 4 panels in series. 14 panels is a bit of a restrictive number only leaving you one option. 12, 15, and 16 have a couple of options.

[Sunking]

Sunking

I am in San Jose CA and the battery bank is 24 volts. On the 15 panels piece I have been considering adding a 15th panel to the array.

24 volt battery and 14 or 15 panels? Something is not right here. What wattage are those panels, and how many controllers are you using?.

Here is what I am driving at. The largest controllers out there are 80 amp MPPT controllers. At 24 volt battery the highest panel wattage you can run depending on what manufacture you use is around 2000 watts on the low end for an Outback and up to around 2600 watts on a Midnite Solar controller.

Even if your total wattage is within limits, you have to be pushing the maximum limit. This system SCREAMS 48 VOLT battery. It would save you some money up front in material cost, more efficient, and allow room for growth. I seriously recommend you reconsider battery voltage. At 48 volts depending on controller gives you room to grow up to 4000 to 5020 watts

[rubiks1]

Sunking

Here is all of the details. 5.2 kw grid tie system is what I have currently, 13 panels on the west pitch roof array and 13 panels on the flat south west array. The idea (cause its not done yet so its not a plan ) is to take one panel off of the west facing array and move it to the south west array to make 14 (there is room on the rack). The remaining 12 will stay on the pitch roof and be controlled by my grid tie inverter. The 14 will be connected to a classic 150 charge wired in series to make 7 strings then go to a midnight solar 12 slot combiner box with breakers combined up to a 4 ga wire for the pos and neg and run that to the midnight solar epanel.

Also I have a 940 watt (4 panels) off grid battery system with a Outback FM60 and a Outback GVFX3524 inverter and 8 agm batteries at 24 volts. I built this system because of all of the power outages we were having 2-3 years ago. Looking back now I probably should have gone for the 48 volt outback inverter but its done. So the idea is to move over 2800 watts of panels to the outback. Per your last post you are 100% correct that should be 48 volts. I did talk to midnight solar and it will max out the controller at 24 volts.

Thanks

24 volt battery and 14 or 15 panels? Something is not right here. What wattage are those panels, and how many controllers are you using?.

Here is what I am driving at. The largest controllers out there are 80 amp MPPT controllers. At 24 volt battery the highest panel wattage you can run depending on what manufacture you use is around 2000 watts on the low end for an Outback and up to around 2600 watts on a Midnite Solar controller.

Even if your total wattage is within limits, you have to be pushing the maximum limit. This system SCREAMS 48 VOLT battery. It would save you some money up front in material cost, more efficient, and allow room for growth. I seriously recommend you reconsider battery voltage. At 48 volts depending on controller gives you room to grow up to 4000 to 5020 watts

[inetdog]

Thanks Sunking. HMM what does -2 mean? 90c and wet

The difference between most alphabetic insulation types and the corresponding type with the -2 suffix is indeed that under some circumstances (90C rated terminals at both ends of the wire) you can use the 90C insulation temperature rating to calculate the allowed ampacity of the wire. On a roof with high ambient temperature plus the so called "roof adder" for exposure of the conduit to sunlight, using the 90C rating can be important.
In some cases the -2 indicates that the 90C rating can be used for both wet and dry conditions instead of for dry conditions only.

[Sunking]

Thanks Sunking. HMM what does -2 mean? 90c and wet

Correct.

[rubiks1]

Thanks for that info inetdog. That is one reason I like these forums. You learn stuff
Take care!!

The difference between most alphabetic insulation types and the corresponding type with the -2 suffix is indeed that under some circumstances (90C rated terminals at both ends of the wire) you can use the 90C insulation temperature rating to calculate the allowed ampacity of the wire. On a roof with high ambient temperature plus the so called "roof adder" for exposure of the conduit to sunlight, using the 90C rating can be important.
In some cases the -2 indicates that the 90C rating can be used for both wet and dry conditions instead of for dry conditions only.