What’s your thoughts on wire size

[markmissouri]

I’m putting in a 7400 kw solar system , it has micro inverters that converted to 220 volts at the ground mount array which is 75 foot away from the disconnect, what size wire should I use ? I was thinking #6 direct bury.

 

[wyliesdiesels]

what country are you in?

220v is not used in the US

 

[mm08822]

I doubt you are putting in a 7400kw array. How about 7400w?

Get the cut sheets for the micro inverters you intend to use. There is a max ocp requirement on the ac side of the inverter.

For example enphase iq7 and iq7+ require max of 20a. So you would need 2 circuits for your 7400w array.

#12's would be fine for each circuit.

 

[dcg9381]

I’m putting in a 7400 kw solar system , it has micro inverters that converted to 220 volts at the ground mount array which is 75 foot away from the disconnect, what size wire should I use ? I was thinking #6 direct bury.

I have a 6KW system (6000 watts). I have an inverter, not micro-inverters and I have not setup or installed a combiner for micro-inverters.

Best guesses on this based on what you posted, subject to new information:
7400 watts / 220v = 33.6A

if you're actually doing:
7400 watts / 240v = 30.8A

So the rough math is that you want to a breaker at 120% this (double check your inverter manual), it's most likely a 40A dual-pole breaker on the grid side. For 75 feet, at 3% drop, it looks like #8 copper to me. #6 would certainly work, but appears to be unnecessary.

 

[markmissouri]

Thanks dcg9381

 

[markmissouri]

Looks like I have to go with #6 as the micro inverter kicks off with a 2% drop

 

[dcg9381]

Mark, can you post a reference to your microinverter?
I'm not sure you're thinking about it right. The big inverters that I deal with are really "converters/inverters" - meaning that they can hit whatever output voltage they want. They have to in order to account for grid variations.

I might, off cuff, consider the microinverter to be the source.. But I don't know how these things are coupled.

Reading another microinverter manual (Enphase):
"But PV systems with inverters generate electricity instead of consume electricity, so voltage actually rises at the AC terminals of inverters. "

Most of the manuals that I've read have some indication on wire selection..

 

[mike93lx]

Thanks dcg9381

You would be wise to not ignore the first couple posters... They are electricians.

 

[mm08822]

Looks like I have to go with #6 as the micro inverter kicks off with a 2% drop

Where did you get the 2% value from? Typical default range for micro inverter output is 211-264vac. I’ve looked at several specs and not seen “%” rating. (Not going to Easter egg hunt either.)

If you were using enphase iq7/7+ inverters and it had to raise the output voltage to a worst case of 264 vac to backfeed into the grid, the vd @16a per ckt would be:
#12 => 1.58% vd = 4.17v. The grid voltage could be as high as 259.8 vac.
#10 => 0.95% vd = 2.6v. The grid voltage could be as high as 261 vac.
#8 => 0.63% vd = 1.7v. The grid voltage could be as high as 262.3 vac.

This assumes you have the 20A limit on the ac side of the inverters and run 2 ckts back to the main panel. I haven’t seen a micro inverter that permits a 40 a ckt.

What are the voltage swings on your grid?

What is the buss ampacity of the main panel and the main cb rating?

Not sure why the inverter choice is such a secret. You want real answers….provide some real info. If you don’t know what you will be using say so. You can get some design inputs here.

And the panel specs.

 

[dcg9381]

Thanks dcg9381

FYI - it wasn't meant as a complete answer to your question. I'm trying to fill in the gaps that you're leaving. There are some guys here that are *much* better than me. Provide full specs, you'll get the best answer possible.

 

[markmissouri]

So what kind of jerk asks what country your from.

 

[mike93lx]

So what kind of jerk asks what country your from.

You won't do well here.

The kind of jerk that cares what code needs to be followed

 

[wyliesdiesels]

So what kind of jerk asks what country your from.

Ummm we get a number of members who are outside the US and ask code questions.

I only know US NEC code. The US doesnt use 220v...

You said 220v and had no location listed in your profile so for all i know, you could be overseas in a country that does use 220v.

Thus any help i give you could be wrong...

Some food for thought...

 

[jeepxj]

I doubt you are putting in a 7400kw array. How about 7400w?

Get the cut sheets for the micro inverters you intend to use. There is a max ocp requirement on the ac side of the inverter.

For example enphase iq7 and iq7+ require max of 20a. So you would need 2 circuits for your 7400w array.

#12's would be fine for each circuit.

7400kw is only 25 acres of panels if my napkin math is right. i don't think a #6 is gona cut it unless you're transforming it up to 125kv.

 

[mm08822]

The bigger q is what kind of jerk starts a thread, goes MIA, but comes back to antagonize people who are trying to help him. ...and completely ignores logical requests for details???

Looks like another thread with no further replies coming to help the OP.