MPP LV6548 AC Wiring Question

[jasonhc73]

I am not an electrician, and your setup may be different, but I believe only one ground bond should be used at the main. Subpanels are not bonded. Please check your local NEC code.

Subpanels are never bonded because you should make a new ground at the sub-panel. The shortest path back to the sub panel (if the neutral is lost) is the new ground near the sub-panel back to the sub panel.

 

[eabyrd]

I have a question about the panel being fed by the inverters. Is it not treated the same way you treat one fed from a transformer as a new source of power? If so the panel it feeds would then have the neutrals and grounds bonded. the reason I ask is that I'm building system using the same inverters. I saw in the videos posted that this has been an issue for the MPP lv6548.

I am also not an electrician so my terminology may be rough / wrong, but I think @Sanwizard is correct in his statement that there should only be a single bonded location per power source.

When the LV6548 is taking power form the grid the bond is made at the service entrance or main panel.
Based on the tests I have run with my LV6548 when in bypass mode, i can confirm it does not create an internal bond in this state. When the LV6548 is in "inverter" mode however it creates an internal bond, and disconnects the AC Input neutral. It maintains connectivity along the AC Neutral Ground. This way earthing remains, but a ground loop / neutral loop is avoided.

Therefore, my sub-panel's neutral is isolated from it's ground.

Hope this helps. The best solution if you are unsure is to hire someone qualified

 

[eabyrd]

Subpanels are never bonded because you should make a new ground at the sub-panel. The shortest path back to the sub panel (if the neutral is lost) is the new ground near the sub-panel back to the sub panel.

Why would you want to give lightning a pathway through your entire electrical system by sticking two ground rods into the earth, and running a wire between them and then to all your expensive electrical appliances?

 

[raurre]

I am also not an electrician so my terminology may be rough / wrong, but I think @Sanwizard is correct in his statement that there should only be a single bonded location per power source.

When the LV6548 is taking power form the grid the bond is made at the service entrance or main panel.
Based on the tests I have run with my LV6548 when in bypass mode, i can confirm it does not create an internal bond in this state. When the LV6548 is in "inverter" mode however it creates an internal bond, and disconnects the AC Input neutral. It maintains connectivity along the AC Neutral Ground. This way earthing remains, but a ground loop / neutral loop is avoided.

Therefore, my sub-panel's neutral is isolated from it's ground.

Hope this helps. The best solution if you are unsure is to hire someone qualified

That was the answer I was looking for. That makes it a different circumstance than a Transformer that never changes state. I am an industrial electrician by trade but could not find any documentation that described how the bypass function of these inverters worked. If they operate as you have described then you would want to keep the panel they feed as a sub if you are using the AC input.

 

[Sanwizard]

Why would you want to give lightning a pathway through your entire electrical system by sticking two ground rods into the earth, and running a wire between them and then to all your expensive electrical appliances?

My DC side is grounded by the solar panels using a seperate ground rod ONLY for the DC side, and only for the panels, mounts, and combiner box.

 

[raurre]

My DC side is grounded by the solar panels using a seperate ground rod ONLY for the DC side, and only for the panels, mounts, and combiner box.

That is how I plan to connect my DC side as well. I had noticed a few people seeming to have a problem with how to connect the first panel after the inverter AC output. I apricate the information from someone who has one in operation.

 

[eabyrd]

My DC side is grounded by the solar panels using a seperate ground rod ONLY for the DC side, and only for the panels, mounts, and combiner box.

My panels frames are earthed, but not the wiring. The DC wiring is earthed through the main panel ground using the battery negative.

my panels are earthed using a dedicated wire, but the same spike as the rest of the structure

 

[Sanwizard]

That is how I plan to connect my DC side as well. I had noticed a few people seeming to have a problem with how to connect the first panel after the inverter AC output. I apricate the information from someone who has one in operation.

My MPP inverters are "non-Isolated", whatever that means (I assume no transformer), so the manual indicated the panels should not be grounded. I did a panel ground anyway, including lightning protection, and all is working fine.
I do need to update the lightning protection from the cheapo Delta to Midnight Solar though.

 

[eabyrd]

My MPP inverters are "non-Isolated", whatever that means (I assume no transformer), so the manual indicated the panels should not be grounded. I did a panel ground anyway, including lightning protection, and all is working fine.
I do need to update the lightning protection from the cheapo Delta to Midnight Solar though.

Agreed, the “panels” themselves should be grounded

thisis from the LV6548 manual

WARNING: Because this inverter is non-isolated, only three types of PV modules are acceptable:
single crystalline, poly crystalline with class A-rated and CIGS modules. To avoid any malfunction, do not connect any PV modules with possible current leakage to the inverter. For example, grounded PV modules will cause current leakage to the inverter. When using CIGS modules, please be sure NO grounding.

 

[Sanwizard]

Agreed, the “panels” themselves should be grounded

Do a search under resources on grounding for some excellent info.

Grounding details for specific make/model of inverters​

 

[eabyrd]

Do a search under resources on grounding for some excellent info.

Grounding details for specific make/model of inverters​

Know it well

 

[raurre]

My panels frames are earthed, but not the wiring. The DC wiring is earthed through the main panel ground using the battery negative.

my panels are earthed using a dedicated wire, but the same spike as the rest of the structure

I like the term earthed it makes it much easier to understand for most people. What you have describe is exactly what i was looking for. Thanks for your help. How large off a load are you putting on your system on average? I have a 4500 watt average in the summer when the AC is running. That is almost continuous since they are inverter based units that run on very long cycles. I was wondering how the units will hold up to the work. my system will be 608 AH Lifepo4 battery bank, 2 lv6548 inverters and 32 Sunpower 435w panels.

 

[eabyrd]

I like the term earthed it makes it much easier to understand for most people. What you have describe is exactly what i was looking for. Thanks for your help. How large off a load are you putting on your system on average? I have a 4500 watt average in the summer when the AC is running. That is almost continuous since they are inverter based units that run on very long cycles. I was wondering how the units will hold up to the work. my system will be 608 AH Lifepo4 battery bank, 2 lv6548 inverters and 32 Sunpower 435w panels.

Since October 17 the average load is about 800 watts in line mode, a bit less in battery (luck of the draw thus far). I have battery discharge current limited to 90 Amps just cause I do. I have them set to run from 54 to 51 volts daily then kick back to the grid. I only allow solar charging by default so they recharge during the day. I only have 2000 watts of panels so some days they don't make it all the way back to 54 volts. When that happens I manually allow grid charging at up to 30 Amps. I have 51 volts as the low-end cutoff so that if the grid does go out I have some power left. 51 volts is about 25 to 30 percent SOC with my batteries. I also have 100 AH of lead I can bring online if shit gets really desperate (it is still good, why throw it out)

My critical loads include:
1. both air handlers, but not the AC compressors. this allows me to have heat (gas) in the winter, in the summer if the grid goes away the fan would move air.
2. Living areas which are all LED lit, and have ceiling fans to aid in cooling as needed. With LEDs living spaces use precious little power
3. Kitchen outlets (one of 2 20-amp circuits)
4. Microwave outlet
5. Bathroom GFIs (2 of 2 20-amp circuits).
6. Hot water heater (showers), and both fridges (food, beer).

Highest real world draw I have seen was about 4800 watts when the microwave, toaster oven, coffee pot, and both air handlers were running at supper time in Nov1. Nov-2 we came close over breakfast. I ran a test the day I hooked it up by running around and flipping on basically everything I could think of (wife was out at time which is why I was moving all my loads then [the secret of a happy marriage] so nobody saw me do this thankfully) and the draw was 5300 watts or about 82%. I think that's a fair margin of safety.

View attachment 71192

​

 

[jasonhc73]

Why would you want to give lightning a pathway through your entire electrical system by sticking two ground rods into the earth, and running a wire between them and then to all your expensive electrical appliances?

CALL THE NFPA and ask them.

Contact NFPA

NFPA is headquartered at 1 Batterymarch Park, Quincy, Massachusetts, 02169, USA. We are a global nonprofit organization, established in 1896, devoted to eliminating death, injury, property and economic loss due to fire, electrical and related hazards.

www.nfpa.org

 

[eabyrd]

CALL THE NFPA and ask them.

Contact NFPA

NFPA is headquartered at 1 Batterymarch Park, Quincy, Massachusetts, 02169, USA. We are a global nonprofit organization, established in 1896, devoted to eliminating death, injury, property and economic loss due to fire, electrical and related hazards.

www.nfpa.org

your job, and I am not an electrician. I will only refer you to my sources which say that with few exceptions for truly separate systems multiple electrodes are “unnecessary and possibly dangerous”

Auxiliary grounding electrode for an array

I know nothing of PV systems. But was wondering if you do decide to have an auxiliary grounding electrode. Do you have to have a bonding jumper to terminate in the intersystem bonding connection device like cable/comms/satillite does Or does it being connected the the EGC suffice for bonding...

forums.mikeholt.com

best of luck

 

[jasonhc73]

your job, and I am not an electrician. I will only refer you to my sources which say that with few exceptions for truly separate systems multiple electrodes are “unnecessary and possibly dangerous”

Auxiliary grounding electrode for an array

I know nothing of PV systems. But was wondering if you do decide to have an auxiliary grounding electrode. Do you have to have a bonding jumper to terminate in the intersystem bonding connection device like cable/comms/satillite does Or does it being connected the the EGC suffice for bonding...

forums.mikeholt.com

best of luck

You asked.

You want to do something contrary to their code. Have at it.

 

[eabyrd]

NEC serves me well, and only requires one. In fact, while you didn't say what code you're trying to follow auxiliary electrodes have been removed from the 2017 and 2020 NEC

 

[Blueprint24]

I am also not an electrician so my terminology may be rough / wrong, but I think @Sanwizard is correct in his statement that there should only be a single bonded location per power source.

When the LV6548 is taking power form the grid the bond is made at the service entrance or main panel.
Based on the tests I have run with my LV6548 when in bypass mode, i can confirm it does not create an internal bond in this state. When the LV6548 is in "inverter" mode however it creates an internal bond, and disconnects the AC Input neutral. It maintains connectivity along the AC Neutral Ground. This way earthing remains, but a ground loop / neutral loop is avoided.

Therefore, my sub-panel's neutral is isolated from it's ground.

Hope this helps. The best solution if you are unsure is to hire someone qualified

WOW, very good explanation and exactly what I've been looking for. Thank you. Thank you ALL really Sanwizard, DanF, eabyrd, everyone. I'm wiring up the AC side of my build now, I'll post some photos once I finish LV6548 x2 split with 280ah x16 lifepo4. Here is a diagram of what I'm doing if anyone is bored.... sub panel has NO bonded neutral/ground. Main is bonded, only. I sent this diagram to MPP also and it took me a few (hence #3) lol

 

[raurre]

WOW, very good explanation and exactly what I've been looking for. Thank you. Thank you ALL really Sanwizard, DanF, eabyrd, everyone. I'm wiring up the AC side of my build now, I'll post some photos once I finish LV6548 x2 split with 280ah x16 lifepo4. Here is a diagram of what I'm doing if anyone is bored.... sub panel has NO bonded neutral/ground. Main is bonded, only. I sent this diagram to MPP also and it took me a few (hence #3) lol

Looking forward to seeing pictures of your system design. I just started my build posted a few pictures in the show and tell. If i can get all of my parts in I'll be able to do some testing.

 

[eabyrd]

WOW, very good explanation and exactly what I've been looking for. Thank you. Thank you ALL really Sanwizard, DanF, eabyrd, everyone. I'm wiring up the AC side of my build now, I'll post some photos once I finish LV6548 x2 split with 280ah x16 lifepo4. Here is a diagram of what I'm doing if anyone is bored.... sub panel has NO bonded neutral/ground. Main is bonded, only. I sent this diagram to MPP also and it took me a few (hence #3) lol

Your picture has a ground loop. Lose the green EGC from the junction box to the 3-pole double throw switch. The EGC running through the inverter circuit will do