diy solar

diy solar

Should I earth ground this system?

Code or not, for a ground array, I personally would definitely run an independent isolated ground as to NOT provide an easy path for the lightning energy back into the house(no ground wire between array and building). I’d have surge arrestors close to the array/structure that ties into the array’s ground and fast blow fuses in the same box. Then back at the house, I’d have another surge arrestor, but this arrestor would grounded to the building system ground because once it makes it there you don’t want any voltage potential difference within the structure. If you do run a ground wire between the building and remote array AND your array’s footing is metal in concrete or earth or you also added a ground rod at the array, you do create a ground loop. Does it matter? Sometimes. Disclaimer; do what your code tells you to.
 
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Thanks for the replies. Something like this you'd think would be simple. It's not like I don't know anything about electrical issues, I did work in the electronics industry for 30 years but none of it is really applicable here.

For safety sake, like if the positive panel voltage shorts to the frame, you would want that ultimately directed thru the ground wire back to the earth ground at the service pole panel, correct? So, wouldn't it be better to run it directly to that panel instead of back to the inverter's ground? Or does it really matter?

I understand you probably need surge arrestors at the array and at the inverter for lightning strikes. Any suggestions/recommendations for these? Could one type do the job for both locations?
 
In the case where PV negative is already connected to chassis by some path (e.g. negative through charge controller goes to negative of battery and that is grounded),
If PV positive shorts to frame, the frame would become high voltage relative to earth. If PV frame had separate ground rod, the dirt right at the rod would be same voltage but some distance away would be lower. The resistance of grounding to earth is required to be under 25 ohms for U.S. residential installations, which is not a dead short. If you touch somewhere on the array frame while standing on the dirt, you could get a shock.
This is the reason for a wire back from array frame to chassis of inverter/charge controller.

Many systems have PV floating, but there is internal coupling to AC. A couple people here have reported getting a shock and measuring voltage from PV frame or metal roof on a second building relative to a metal ladder. Wire back to all equipment including inverter and utility entrance panel keeps those at same voltage.

With all metal bonded together, there is low enough resistance to short out the voltage, keep them at the same voltage.
Maybe the would be higher than earth, so a ground rod (that 25 ohms or less) holds the voltage down to same as the dirt you're standing on. No current to speak of, so good enough. One ground rod at service entrance takes care of that.

With AC wires run to two buildings, like my house and garage 100' away, code requires a rod for each. It is also bonded to pipes, foundation steel, etc. I think that is so if I touch chassis at other building, which provides a wire back to ground rod at first building, there could be some voltage drop (current through wires x resistance) so hold dirt at same potential.

Mike Holt doesn't like an additional ground rod because lightning strike nearby would use rod, wire, rod as lower resistance path to spread out across the ground, through your system. It is just the ground wire, but running parallel to PV+/-, it would induce common-mode current in them (inductively). Voltage bounce will also induce (capacitively). But by having not electrocuted yourself you will be able to buy new equipment to replace whatever is damaged.

Probably no lightning arrestor at array. If lightning hits face of panel with PV cells, there will be a hole burned in them. Assume it hits metal frame or structure, follows ground wire and/or footings into earth. For a lightning prone area, consider lightning rods above array, wire draped between them, insulated from array frame and grounded separately.

Back at the inverter or where ever PV wires enter, a lighting arrestor between PV+/PV-, PV+/ground, PV-/ground would clamp the voltages low enough that hopefully electronics doesn't see too much. Some of my PV inverters from SMA have MOV between those wires.


Midnight has a good unit with MOV between the wires, also LED showing their protection is present, or they have blow and need replacement. Various models for different DC and AC voltages (Surges on utility grid are a normal occurrence and you want protection there as well.)


My inverters are spec'd to operate up to 600VDC. The MOV supplied by SMA clamp to about 800 ~ 1000V (higher for high current surge.) That is OK because equipment can take brief transients; Midnight mentions about 2500V spikes as part of compliance testing. I ended up buying a surplus industrial surge suppressor which clamps at 200V, detailed in same thread. That will protect better but trigger more often and wear out sooner.

Lightning is more of a problem in some parts of the country. Utility line surges are normal, from switching of loads and utility company transformers & capacitors. There can also be lightning strikes to power lines.

Don't bother with Delta lightning arrestors. They may be useful for extreme events at higher voltages, but neither Midnight nor I (nor the lab Midnight went to) could get them to fire in the low kV range.

 
In the case where PV negative is already connected to chassis by some path (e.g. negative through charge controller goes to negative of battery and that is grounded),
If PV positive shorts to frame, the frame would become high voltage relative to earth. If PV frame had separate ground rod, the dirt right at the rod would be same voltage but some distance away would be lower. The resistance of grounding to earth is required to be under 25 ohms for U.S. residential installations, which is not a dead short. If you touch somewhere on the array frame while standing on the dirt, you could get a shock.
This is the reason for a wire back from array frame to chassis of inverter/charge controller.

Many systems have PV floating, but there is internal coupling to AC. A couple people here have reported getting a shock and measuring voltage from PV frame or metal roof on a second building relative to a metal ladder. Wire back to all equipment including inverter and utility entrance panel keeps those at same voltage.

With all metal bonded together, there is low enough resistance to short out the voltage, keep them at the same voltage.
Maybe the would be higher than earth, so a ground rod (that 25 ohms or less) holds the voltage down to same as the dirt you're standing on. No current to speak of, so good enough. One ground rod at service entrance takes care of that.

With AC wires run to two buildings, like my house and garage 100' away, code requires a rod for each. It is also bonded to pipes, foundation steel, etc. I think that is so if I touch chassis at other building, which provides a wire back to ground rod at first building, there could be some voltage drop (current through wires x resistance) so hold dirt at same potential.

Mike Holt doesn't like an additional ground rod because lightning strike nearby would use rod, wire, rod as lower resistance path to spread out across the ground, through your system. It is just the ground wire, but running parallel to PV+/-, it would induce common-mode current in them (inductively). Voltage bounce will also induce (capacitively). But by having not electrocuted yourself you will be able to buy new equipment to replace whatever is damaged.

Probably no lightning arrestor at array. If lightning hits face of panel with PV cells, there will be a hole burned in them. Assume it hits metal frame or structure, follows ground wire and/or footings into earth. For a lightning prone area, consider lightning rods above array, wire draped between them, insulated from array frame and grounded separately.

Back at the inverter or where ever PV wires enter, a lighting arrestor between PV+/PV-, PV+/ground, PV-/ground would clamp the voltages low enough that hopefully electronics doesn't see too much. Some of my PV inverters from SMA have MOV between those wires.


Midnight has a good unit with MOV between the wires, also LED showing their protection is present, or they have blow and need replacement. Various models for different DC and AC voltages (Surges on utility grid are a normal occurrence and you want protection there as well.)


My inverters are spec'd to operate up to 600VDC. The MOV supplied by SMA clamp to about 800 ~ 1000V (higher for high current surge.) That is OK because equipment can take brief transients; Midnight mentions about 2500V spikes as part of compliance testing. I ended up buying a surplus industrial surge suppressor which clamps at 200V, detailed in same thread. That will protect better but trigger more often and wear out sooner.

Lightning is more of a problem in some parts of the country. Utility line surges are normal, from switching of loads and utility company transformers & capacitors. There can also be lightning strikes to power lines.

Don't bother with Delta lightning arrestors. They may be useful for extreme events at higher voltages, but neither Midnight nor I (nor the lab Midnight went to) could get them to fire in the low kV range.

Thanks for the detailed reply. That's certainly a lot to digest, but I need to understand it before I proceed.

I read thru a bit of your MOV tests using a hypot. I am very familiar with hypot testing, as I did that while I was a tester at at&t, and later as a qualification tech with Tyco Electronics.

Those Midnite arrestors look familiar, I've seen them on various YouTube DIY vids.
 
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The PV negative is attached to the inverter chassis ground? Huh? Something I never looked at. I do know that if the inverter is on and running you don’t want to touch anything connected to the PV + input even if there’s no panel connected. Don’t ask.
 
Generally you don't mess with PV- or PV+, just wire to MPPT inputs.
The SCC or inverter can ground PV- (or PV+) internally if it wants to. In some of my Sunny Boy that is through a 1A fuse, part of ground-fault protection. I have negative grounded, positive grounded, and non-grounded inverters.
The non-grounded are transformerless, typically carry a voltage above peak of grid AC to below negative peak, as a DC bias (more or less depending on Vmp and buck/boost design.) On 3-phase, also carries common-mode AC (about 60Vrms for 120/208Y and 138Vrms for 277/480Y)
Sometimes battery negative is grounded; that may be code requirement. That would likely ground PV- in a DC coupled system.

Yes, some people have reported backfeed of DC or AC to PV inputs, got a shock without PV panels connected. Also found AC on PV array frame or RV chassis (high impedance, but needs grounding to eliminate voltage.)
Shut things off and confirm zero volts (both AC and DC scales) before touching anything.
 
In the case where PV negative is already connected to chassis by some path (e.g. negative through charge controller goes to negative of battery and that is grounded),
If PV positive shorts to frame, the frame would become high voltage relative to earth. If PV frame had separate ground rod, the dirt right at the rod would be same voltage but some distance away would be lower. The resistance of grounding to earth is required to be under 25 ohms for U.S. residential installations, which is not a dead short. If you touch somewhere on the array frame while standing on the dirt, you could get a shock.
This is the reason for a wire back from array frame to chassis of inverter/charge controller.

Many systems have PV floating, but there is internal coupling to AC. A couple people here have reported getting a shock and measuring voltage from PV frame or metal roof on a second building relative to a metal ladder. Wire back to all equipment including inverter and utility entrance panel keeps those at same voltage.

With all metal bonded together, there is low enough resistance to short out the voltage, keep them at the same voltage.
Maybe the would be higher than earth, so a ground rod (that 25 ohms or less) holds the voltage down to same as the dirt you're standing on. No current to speak of, so good enough. One ground rod at service entrance takes care of that.

With AC wires run to two buildings, like my house and garage 100' away, code requires a rod for each. It is also bonded to pipes, foundation steel, etc. I think that is so if I touch chassis at other building, which provides a wire back to ground rod at first building, there could be some voltage drop (current through wires x resistance) so hold dirt at same potential.

Mike Holt doesn't like an additional ground rod because lightning strike nearby would use rod, wire, rod as lower resistance path to spread out across the ground, through your system. It is just the ground wire, but running parallel to PV+/-, it would induce common-mode current in them (inductively). Voltage bounce will also induce (capacitively). But by having not electrocuted yourself you will be able to buy new equipment to replace whatever is damaged.

Probably no lightning arrestor at array. If lightning hits face of panel with PV cells, there will be a hole burned in them. Assume it hits metal frame or structure, follows ground wire and/or footings into earth. For a lightning prone area, consider lightning rods above array, wire draped between them, insulated from array frame and grounded separately.

Back at the inverter or where ever PV wires enter, a lighting arrestor between PV+/PV-, PV+/ground, PV-/ground would clamp the voltages low enough that hopefully electronics doesn't see too much. Some of my PV inverters from SMA have MOV between those wires.


Midnight has a good unit with MOV between the wires, also LED showing their protection is present, or they have blow and need replacement. Various models for different DC and AC voltages (Surges on utility grid are a normal occurrence and you want protection there as well.)


My inverters are spec'd to operate up to 600VDC. The MOV supplied by SMA clamp to about 800 ~ 1000V (higher for high current surge.) That is OK because equipment can take brief transients; Midnight mentions about 2500V spikes as part of compliance testing. I ended up buying a surplus industrial surge suppressor which clamps at 200V, detailed in same thread. That will protect better but trigger more often and wear out sooner.

Lightning is more of a problem in some parts of the country. Utility line surges are normal, from switching of loads and utility company transformers & capacitors. There can also be lightning strikes to power lines.

Don't bother with Delta lightning arrestors. They may be useful for extreme events at higher voltages, but neither Midnight nor I (nor the lab Midnight went to) could get them to fire in the low kV range.

At the recommendation of @FilterGuy in the ex6500 thread, I was going to run hot, neutral and ground from the service panel (via a 60A breaker) to the inverter AC input. From the inverter AC output just a hot and neutral would run back to the crit load panel. From there, I would run a ground wire back to the house subpanel ground bar. So, since the output ground connection of the inverter isn't being used here, could I run the ground wire from the array and hook into the output ground? Also, what gauge should the ground wire be between the panel frames, and then back to the inverter? Something like a bare 6 gauge wire on the frames, and 10ga THHN back to the inverter?

So, regarding the Midnite arrestor, I would connect it at the inverter, with the MOV's connected between PV+/PV-, PV+/ground, and PV-/ground? Which model would I need? Since this would be to protect the PV (DC) inputs, would it be the MNSPD-600-DC device? The max VoC rating of the PV inputs is 500V.

Regarding lightning here, we are on the side of a hill, slightly exposed, but we really don't have a lot of lightning strikes here. We are about 300ft below the hilltop behind our house, and about 100-150ft above the valley floor.
 
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service panel ... inverter ... crit load panel ... house subpanel ground bar

Will ground conductor connect all these? Or did you mean two separate ground networks connected only by dirt?
there should be copper connecting all of them together.

Ground wires for AC circuits are smaller than current-carrying conductors because only needs to carry fault current long enough to trip breaker.

Ground wire to PV panel frames has to carry fully current continuously since likely no breaker ever trips.
All wires (current carrying and ground) should have ampacity 1.56 x Isc. PV strings would use Isc of the single string, but if combined in one wire that would be Isc of the array, and ground would be Isc of the array.

Lightning arrestor at the MPPT input, or at a combiner box. The Midnight have multiple wires and internally the MOV are wired in delta configuration. So you just connect one each to PV+, PV-, ground. Voltage rating of device needs to be equal or greater than max Voc, so if Voc can reach 500V then yes the 600V model. If never reaches 300V, then the 300V model would provide more protection.

Maybe lightning isn't a big deal for you, won't be close. It can inductively couple something, I don't know how much.
 
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