Help needed wiring AC Disconnect....

If I understand your questions correctly, the Line side of the disconnect should face the main panel/power meter. And the load side should be towards the GT inverters.

The Neutral should be a straight run from the main panel to the GT Inverter neutral connection (2x GT inverters, 2x Neutral Runs). On a typical 240 VAC GT inverter, the neutral carries next to zero current... Generally just used by the GT inverter as a "qualifying" signal (that Neutral to L1 and/or L2 line voltages are correct--And there is the neutral is not "broken"). There may also be a qualification of safety ground to neutral/L1/L2 (to check that ground connections are good). You still want the metal chassis of the GT inverter(s) to be safety grounded in case there is a Hot to Ground short in the future.

Regarding grounding... Any metal electrical box (such as the Disconnect, GT inverter, etc., that contains AC power (or even DC from array), should be safety grounded (by metal conduit and/or green/bare copper wire--Depending on your local code/installation). You do not want a short from Hot to Metal to energize the metal enclosure and electrocute somebody.

Did I get this right?

-Bill

DR,

I am fine with you keeping this thread open... It is discussing your system and a little history does not hurt.

I think--That "ungrounded" is referring to the solar panel connections... The transformer based GT systems usually (always?) grounded one leg of the solar panels through a fuse/breaker (typically the negative lead) and used a fuse between negative and safety ground. If there was, for example, a short between Array Positive and safety ground, it popped the fuse (or circuit breaker) and shut down the GT inverter (or solar charge controller/etc. in an off grid system).

With transformerless GT inverters (transformer = big, heavy, lots of copper, and expensive), neither the positive or negative array connections are ground referenced. Basically they are referenced to the 240 VAC line (switching/inductors/etc.).

For North American 120/240 VAC split phase power, we have the ground referenced Neutral, and L1/L2 (Lx to neutral=120VAC; L1 to L2 = 240 VAC). So--Even the L1/L2 leads are ground referenced (through the center-tap of the pole transformer)--Just not "at ground" --- Unlike Neutral which is ground bonded back at the main panel/cold water pipe/main home ground rod so always at or very close to ground.

What does that mean for wiring an "ungrounded"/transformerless GT inverter? (Remember, I am no expert at this, and have never had any training by any GT Solar Mfg.)--As I understand... You simply wire as normal.

Green/Bare copper wire from safety ground (in main panel, possibly via metal conduit) that connects all electrical boxes and system chassis (such as the GT inverter) as normal/appropriate. There is simply no internal to the GT inverter connection between Solar +/- to any local ground or fuse or breaker (some GT inverters had an option for  negative or positive grounding--From many years ago when one brand of solar panels needed positive grounding for proper/long term operation).

The green wire "safety ground" is there to ensure that no exposed "metal box/chassis" becomes "hot" and can electrocute somebody--Typically a short circuit to chassis will trip a branch circuit breaker back in the main panel (or sub panel, internal fusing in device, etc.). That is what the safety ground is supposed to do (carry fault current back to the source and trip the breaker).

For grounding of the solar rack mounts and panel frames. Of course, you just follow code as normal. If you do not have lightning in the area, you could run the array ground to the green grounding screw inside the GT inverter (follow the installation instructions and code/inspector requires for your area).

If you have lighting in your area... My suggestion is along the lines of: Run a minimum of 6 AWG copper wire from panels/rack (supposed to be a solid one piece wire, no wire nuts or connections--Although other "permanent" connections like thermal or crimp(?) are allowed) straight down the outside wall to a ground rod at the base of the wall. (Do not bring this lighting ground inside your home/building--Keep outside--And Lightning wants to go to the "perimeter of the building anyway). At the base of the wall/rod, use soft rounded turns... Not right angle (Radio Frequency rules--Right turn make higher "impedance" (complex resistance) and lightning will have a tendency to leave the wire at the right angle and find another path to ground).

I also highly suggest that you connect the "local lightning ground rod" via 6 AWG to the main building ground (cold water pipe, main ground rod, etc.). This is so that if there is a short circuit from array to rack to lightning ground, that the return current will go back to the main panel and trip a circuit breaker--Rather than "energize" the array frames/racking and possibly electrocuting somebody.

The above is a quick suggestion... NEC code has always been a little "weak" on lightning grounding rules. The connection from local ground back to main ground via 6 AWG minimum cabling has not been required in the past--But is really needed for safety. The resistance from a "local ground" back to the building ground can be so high, that the current flow to a local ground short does not allow enough current to flow and trip the branch circuit breaker--Not good. For example, assuming 25 Ohms maximum resistance (limit for NEC as I recall):

• 120 VAC Lx to ground / 25 Ohms = 4.8 Amps current flow (not enough to trip a 15+ Amp breaker)

Does this make sense/answer your questions?

-Bill

To edit your notifications, click on your name and then (perhaps edit account first then) edit preferences:

https://forum.solar-electric.com/profile/preferences/

The menus are sometimes a bit different for me (moderator options)--But the above direct link should work for anyone.

This is from 40 years ago (my last time I helped wire in a main panel)--More or less, the requirement for ground wire from cold water pipe to main panel is 6 AWG bare minimum (up to a 125 or 200 amp panel?). However, at the time, we could also use insulated 8 AWG for ground connection from ground rod to main panel... A big part of the minimum size of the wire was so that "life" (guy with shovel or weed eater) would not break a smaller AWG cable.

Roughly a bare 6 AWG copper wire will "fuse" (burn open) around 600 amps. Enough to trip the main breaker (125 Amps or bigger?) if there is a short.

All wiring and grounding from the main panel through breaker to loads (branch circuits) are based on code for that circuit (i.e., 15 Amp breaker, 14 AWG cable, 20 Amp breaker is 12 AWG, and so on). A simplified chart here:

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

As you can see, material (aluminum or copper) and insulation type affect the current rating of the wire. Also, conduit fill and ambient temperatures affect ratings too (wire in home wall, vs wire in conduit on roof for solar panels).

The actual NEC Code Book has all sorts of tables and deratings based on the above requirements.

The "unbroken" ground wire requirement is from the ground rod/cold water pipe to the ground bus in the main panel. You can use crimp or thermal bonded connections--But cannot use wire nuts or cable clamps. The idea being that "somebody" cannot easily disconnect the ground wire (somewhere in wall/j-box) and easily defeat the safety ground system.

For devices (appliances, etc.) there is a separate safety ground wire connection. And if there is need for additional ground wire connect on a chassis mounted ground stud (for example), the safety ground wire has the first nut and lock washer, and any additional device grounds  are "stacked" on top of the safety ground+nut (again, so that somebody working on the device must physically disconnect the safety ground, and not accidentally disconnect while working on other portions of the device).

I don't believe there is an "unbroken" ground wire requirement for branch circuits... Just run (for example) a ground wire from the main panel ground to the first box/switch box. And then run a second ground wire from that box to the GT inverter's chassis ground, etc....

-Bill

Found copper single hole lugs that could be used for ground connections in a box (I think):

https://www.homedepot.com/s/copper%2520single%2520hole%2520%2520lug?NCNI-5

-Bill

Homedepot also has some other lugs:

https://www.homedepot.com/s/copper%2520lug?NCNI-5

-Bill