Proper Grounding for Sunny Boy 6048 Inverter?

kris25 · August 2022

I'm currently working on setting up a SMA 6048 inverter. The DC inputs accept up to 3/0 gauge +, - and ground. Is a #6 ground acceptable? Running a 2/0 ground to match my + and - seems like way too much.

This is what's set up on it:
(1) SMA 6048 single phase, 120V
(2) Banks of 4 Renogy Sealed Gel Batteries (12V 200AH each)
30' Romex 6/2 wire from inverter to electrical box

This set-up is off grid with a generator to charge the batteries. Also, on top of the correct ground size can I run this to it's own grounding pole? The electrical box is on the other side of the cabin about 30' away.

BB. · August 2022

Welcome to the forum Kris25,

Ideally, you should refer to the NEC (National Electric Code in much of USA) or similar for exact requirements.

As a simplified example, the size of current carrying conductors vs equipment/panel grounding conductors (note copper vs aluminum--AL needs heavier cable for "same" copper current ratings):

https://learnmetrics.com/ground-wire-size-chart-nec-grounding-conductor-size-chart/

Size Of Copper Wire (AWG or kcmil):	Copper Grounding Electrode Conductor Size (AWG or kcmil)
8 AWG Copper Wire	8 AWG Copper Ground Wire
6 AWG Copper Wire	8 AWG Copper Ground Wire
4 AWG Copper Wire	8 AWG Copper Ground Wire
3 AWG Copper Wire	8 AWG Copper Ground Wire
2 AWG Copper Wire	8 AWG Copper Ground Wire
1 AWG Copper Wire	6 AWG Copper Ground Wire
0 (1/0) AWG Copper Wire	6 AWG Copper Ground Wire
00 (2/0) AWG Copper Wire	4 AWG Copper Ground Wire
000 (3/0) AWG Copper Wire	4 AWG Copper Ground Wire
0000 (4/0) AWG Copper Wire	2 AWG Copper Ground Wire

The SMA manual should list the wiring requirements... But a quick math check:

6,000 Watts * 1/0.85 AC inverter eff * 1/42 VDC battery cutoff voltage = 168 Amps max current

And another simplified NEC AWG vs Insulation vs AWG current rating chart:

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

3/0 is certainly heavy enough cable (higher insulation temperature ratings, smaller AWG can be used).

Another issue to watch out for is cable resistance... ~!68 amps is a lot of current--And "too long" or "too small of AWG" cable can increase voltage drop and cause battery cutoff.

For example... 168 amps @ 3/0 cable @ 46.00 Batt voltage - 42.00 batt cutoff @ xxx feet?

https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=6&necconduit=steel&necpf=1.&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=46&phase=dc&noofconductor=1&distance=48&distanceunit=feet&amperes=168&x=0&y=0&ctype=nec

Result for 48 feet of 3/0 cable @ 168 amps

Voltage drop: 4.03
Voltage drop percentage: 8.76%
Voltage at the end: 41.97

Similar calculations for AC side...

6,000 Watts * 1/115 VAC nominal = 52 Amps max current

Look for 3% max drop on your 115 VAC line...

Note that a 48 volt @ 400 AH is a relatively small battery bank for a 6,000 Watt inverter... GEL batteries do have better high/surge current than flooded cell lead acid batteries.... Typically for a 6 kWatt inverter, would be suggesting a 600 AH@ 48 VDC battery bank minimum.

But the full answer also needs to know your planned loads (Watt*Hours per day, max surge WH, etc.).

Another possible issue--Look at the specifications for your GEL batteries. Max charging and discharging currents can be an issue... If these are your batteries:

https://www.renogy.com/deep-cycle-hybrid-gel-battery-12-volt-200ah/

CHARGING PARAMETERS

Charge Voltage: 13.6V~13.8V
Maximum Continuous Charging Current: 60A
Maximum Continuous Discharging Current: 20A
opc:
Standard Operation Temperature: 77°F±9°F（25°C±5°C）
Storage Temperature: -4~140°F/ -20°C~60°C

Then 60 amps max charge rate per string (actually pretty high charge rate for GEL batteries) and 20 amp max continuous drain (pretty low for GEL batteries)--Almost looks like the battery charge/discharge spects have been reversed(???).

https://www.renogy.com/content/RBT200GEL12-G1/GEL200-Datasheet.pdf

The PDF (above link) has very different specifications (20 amp charging or 10%; discharging... Upwards of 3C or 600 amps discharge current).

Watch charging voltage (and current). In general GEL batteries do not like to be "over charged".

-Bill

kris25 · August 2022

Thanks for all of the info! So I should run a DC ground and AC (main panel) ground to one single location?

What is confusing me the most is that there is currently no ground that I can see in the panel. There is a ground wire in the "generator room" outside the house but it's just coiled behind the breaker boxes and doesn't go to anything. A generator was always the only source of power. Does that explain why the coiled wire was never grounded to anything?

kris25 · August 2022

"Generator Room"

Image: https://us.v-cdn.net/6024911/uploads/editor/xu/wm94tx4c69lj.jpg

Coiled ground going to nothing

Image: https://us.v-cdn.net/6024911/uploads/editor/vk/hqfhe9hfejum.jpg

8/3 Romex that runs from generator room to main panel (before I ran 6/2 from Inverter)

Image: https://us.v-cdn.net/6024911/uploads/editor/kr/blzudme1emr2.jpg

Inverter and batteries (30' from main panel)

Image: https://us.v-cdn.net/6024911/uploads/editor/e7/a20vkxhwazk4.jpg

BB. · August 2022

Kris can you tell us a bit more about the Genset?

120 or 120/240 VAC?

Is your home 120 VAC only or do you have (or plan to use) 240 VAC applicants/well pumps too?

It looks like your main panel is wired for 120/240 VAC and the inverter you have is 120 VAC only...

Questions about Genset/inverter transfer switch?

Bill

kris25 · August 2022

I have a 9000 watt Champion generator that can run either 240 or 120 and I also just got a Honda EU3000is. The Honda is enough to run everything but the shallow well pump. I believe the Honda is only 120 but all I needed was an adapter to the large cord in the first pic.

I only plan on using 120VAC. This is a weekend type cabin. I installed a 120V shallow well pump, have a propane stove, small electric water heater no washer/dryer no AC etc... Just a real simple power usage. The biggest draw (excluding the pump) is probably the refrigerator which is about half the size of a normal fridge.

Proper Grounding for Sunny Boy 6048 Inverter?

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Result for 48 feet of 3/0 cable @ 168 amps

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