Electrical Run - ground wire question

[sodamo]

In the process of taking my cottage off is standalone solar PV electric and hooking in to my main system at the house. You can see the trench work here: http://www.tractorbynet.com/forums/kioti-owning-operating/245828-kb-2375-trench.html

I am running approx 375 ft of #2 copper from my main distribution panel to a sub panel at the cottage. 70AMP breakers, 240 volt. Loss will be just over 3%.

My question is regarding ground wire. Do I need to run 2 separate grounds panel to panel or is a single sufficient. I can buy 3 conductor w/ ground to run in my 2inch conduit. If I need the 2nd ground I suspect I'll have to run 3 separate conductors plus the 2 grounds. Naturally, the 3w/grd would be easier for me to handle. This is not a grd rod issue as there are double rod.

A friend is bringing over a copy of the NEC, but thought I'd tap into the BN brain trust.

David

 

[hr3]

I don't have the book at home but I'm thinking #8 copper for the ground,, and you only need one.. Saying that you will have 3 # 2 copper and 1 #8 copper ground,,
PS don't forget the ground rod and the building,,

Here is a neet chart for you..

electrician2.com Wire Size calculator

 

[trumpeter]

HR3 is right as what he said. The big thing to remember is to seperate the grounds and nuetrals at the cottage and the nuetrals don't get bonded to the panel. They realy do have to be seperate.

 

[sodamo]

Thanks guys, appreciate it.
There are 2 ground rods at cottage from the current solar that will be uninstalled.
So if I understand, my new ground will tie into this ground at the panel. My neutrals will be separate and not bonded to panel.

Another 20 ft of digging and can emplacement the last 50ft of conduit and get a final measure for the cable. At $8/ft, don't want to be short, but don't want too much excess either.

David

 

[John47]

HR3 is right as what he said. The big thing to remember is to seperate the grounds and nuetrals at the cottage and the nuetrals don't get bonded to the panel. They realy do have to be seperate.

Some utilities require the neutral to be grounded at the house service!!
Check your untility to find their requirement!
NEC goes either way.. It's correct to ground the neutral or leave it ungrounded at the house, again, if the utility requires it so will your home insurance company..

 

[sodamo]

Some utilities require the neutral to be grounded at the house service!!
Check your untility to find their requirement!
NEC goes either way.. It's correct to ground the neutral or leave it ungrounded at the house, again, if the utility requires it so will your home insurance company..

Totally, off grid, standalone solar systems - no utility company.

 

[tlbuser]

Totally, off grid, standalone solar systems - no utility company.

Must be one heck of a system. How large of a collector system?

 

[John47]

Totally, off grid, standalone solar systems - no utility company.

Looked like you were saying you were going back on grid from a stand alone solar plant.

My guess then would leave the neutral "floating".

 

[John47]

I'm also putting the parts together to get off grid, I am starting with four 240watt/24 volt panels, one 4Kw Magnum 120/240V stackable Inverter, and four Trojan L16RE-A batteries with a backup wind generator.
All to be upgraded before winter to another 4 solar modules, a second inverter to give us 8Kw and batteries up to three banks of four to give us nearly 1000Ahr capacity.

DON'T forget to ground the negative side of the solar modules and if they don't come with them, add blocking diodes to each module!

 

[sodamo]

Must be one heck of a system. How large of a collector system?

Current house system is 4.5kw, 36x125 panels. 24kw diesel backup gen. This is an exiting system, been online since 2007. Rolls Surrette 1350 amh battery bank, 4 Outback 3048 inverters.

Once I Get the new line hooked up, I'll move the 8 cottage panels (992 watts) to the main and add another 4 panels (560 watts) effectively increasing the system by a third.

 

[tcartwri]

DON'T forget to ground the negative side of the solar modules and if they don't come with them, add blocking diodes to each module!

It depends on the inverter used. In my system the panels are floating with respect to earth ground.

 

[tcartwri]

I am running approx 375 ft of #2 copper from my main distribution panel to a sub panel at the cottage. 70AMP breakers, 240 volt. Loss will be just over 3%.

I would suggest you price aluminum wire for this long of a run. You will be able to go up several wire gauges and still be half the price of the copper.

 

[John47]

I would suggest you price aluminum wire for this long of a run. You will be able to go up several wire gauges and still be half the price of the copper.

That's his statement that confused me thinking he was changing back from solar to grid.
Why on earth not have everything at the house site?? That's an awfully long run of cable.

 

[tcartwri]

That's his statement that confused me thinking he was changing back from solar to grid.
Why on earth not have everything at the house site?? That's an awfully long run of cable.

It's my understanding that is what he is doing. He's moving the small solar array from the cottage up to the existing array on the main house. Then running a feeder line back down to the cottage.

 

[sodamo]

It's my understanding that is what he is doing. He's moving the small solar array from the cottage up to the existing array on the main house. Then running a feeder line back down to the cottage.

That would be correct.

A bit of history: the cottage was built during a series of 2 week visits from shortly after buying the property in 2003 until we moved there in 2005. When we moved in 2005, I built a small solar system. I found a diagram in HomePower magazine, bought panels and some parts via eBay. Worked quite well - as a learning tool. It started with only the 4 sharp 123w panels. My wife lived there while I returned to Ga to finish getting our house to put on the market. Unfortunately, she choose to listen to the neighbors and didn't run the generator nearly enough for the batteries. We nursed about 6 months out of them. We also learned about conservation. I added the 125w panels to improve, changed the charge controller to an Outback MX60, and took much better care of the new batteries. Also replaced the generator with a Honda EU3000i. We lived there until fall of 2007 when our new house was habitable. We sized the house solar with the thought to eventually connect. Last year, I remodeled the cottage, adding a roof to the lanai. Unfortunately, that roof blocks 2-3 hours of morning sun. In April my Honda went on the fritz and estimated 7-800 to repair. So after seriously considering where to relocate my panels, factor in that my batteries are now 6 years old, the loss of my Eu3000i, just seemed time to bite the bullet and consolidate. Yes, it will cost a bit more initially and be more work and take longer, but the long term benefits win out. The panels become part of the main system, I can upgrade my extra charge controller and swap out and have a spare, only one battery bank to maintain, and sell off my freed up inverter and even recover a bit on the extra batteries etc. My main house system was professionally done although I have changed out and improved a couple of minor components this past year. There is also existing room in my combiner box for the 3 new strings of panels. The 4 Outback FX3048 inverters were installed to accommodate the expansion.

I did buy my wire today. 500 ft spools of #2 copper, $749 at HD, minus my military discount. I did briefly consider using larger gauge Alum, but decided to go with the copper, as did my electrician when he ran my other sub panels.

John47 - have you evaluated your wind? My first attempt at expanding my small system was to add an AirX - big mistake for me. I did it based on how windy it was at night and winter. Even though I could see the little light glowing and the needle bounce a bit, I never saw my batteries plus send up in the morning. I often wished I had bought 2 more panels at the time. The L-16s have a mixed reputation around here, then again so do most of the installers. Based on what you have posted, I'd be tempted to suggest just installing a set of golf cart bats and after you have all your generation worked out then install a good set.

 

[John47]

I only need wind as a backup, we are not in a high wind area.
As for batteries, I require high output, and long life, I was considering Nickel Iron at one stage, problem is the very high price, if I was 20 years younger they would be my choice, as they have an infinite life, reasonable output and very light weight together with being a none polluting battery, ie the electrolyte isn't hazardous to the environment. The main drawback is price, and then having to replace the electrolyte every few years.

My main aim is to be off the grid to be as self sufficient as possible, hence having 8 cells giving me around 2Kw of charging power at peak sunlight, plus 400watts of wind power at peak winds.
I also have two auto alternators with good windings I plan to convert to permanent magnet rotors for wind generators.
If I can get 20 plus amps from wind during cloudy days and night periods, I'll be happy, that's 20 amps at 30 plus volts for the 24 volt battery banks.

I have a good open spot for the wind generators on a small hill in one of my fields.