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Old 10-07-2021, 08:49 AM   #1
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Inverter ground connection size

I am upsizing the battery bank in my 5er from two to three 100 Ah Battleborn batteries. I also have a Victron Multiplus 3kw hybrid inverter.

I am using 4/0 cable throughout. When I ordered cable, though, I did not account for the ground wire. Should the ground be the same size as the primary wire, or can it be something smaller? My original installation used 2 AWG for the ground, and I have a lot of 1/0 cable available.

Thanks!
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Old 10-07-2021, 08:51 AM   #2
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Quote:
Originally Posted by JHinman View Post
Should the ground be the same size as the primary wire, or can it be something smaller?

Thanks!

In a word, YES. Inverter to negative should be the same gauge as positive.


Those little electrons do make a round trip!
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Old 10-07-2021, 09:02 AM   #3
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Quote:
Originally Posted by JHinman View Post
I am upsizing the battery bank in my 5er from two to three 100 Ah Battleborn batteries. I also have a Victron Multiplus 3kw hybrid inverter.

I am using 4/0 cable throughout. When I ordered cable, though, I did not account for the ground wire. Should the ground be the same size as the primary wire, or can it be something smaller? My original installation used 2 AWG for the ground, and I have a lot of 1/0 cable available.

Thanks!
No. I use the solid bare ground wire that you can get at Home Depot in the electrical department, which is especially designed for panel and service entrance grounds. You need a ground for the output on the AC side but there should be little if any current flowing on the ground wire.
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Old 10-07-2021, 09:05 AM   #4
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Obviously some confusion.


Are you talking about the 12 VDC wire from negative terminal of battery to inverter?


OR


120 VAC ground wire?
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Old 10-07-2021, 09:10 AM   #5
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S/B interesting. I never refer to the Negative lead as a ground, but then, that's me!
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Old 10-07-2021, 09:16 AM   #6
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Perhaps a better way to say this, both the positive and negative ~12v wires going to the inverter and used to provide the 12v input power to the inverter need to be the same wire size. ~CA
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Old 10-07-2021, 09:31 AM   #7
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BTW, to add to my thoughts and change my answer slightly, while you should have both the pos and neg cables of the same size, and while not up to code for most electrical work, you could simply add a second 2awg conductor to the negative side along with the existing 2awg cable as 2 x 2awg cables are able to carry as much current as 1 x 4/0 awg cable and that would work for you perhaps easiest. If you don't have any more 2awg laying around and if the inverter connection can support it, you could also run a section of 1/0 cable on the negative, again assuming you keep the 2awg already there. ~CA
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Old 10-07-2021, 09:31 AM   #8
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Frankly, never seen an inverter ground lug that could take a cable anywhere nearly that big anyway. Xantrex specs say a minimum of #8 for the ground.
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Old 10-07-2021, 09:34 AM   #9
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My Xantrex/Trace 2000 WATT inverter uses the same size cable for + - & ground


When in doubt go the safe route, oversize.
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Old 10-07-2021, 09:35 AM   #10
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Best practice is to follow instructions in the installation manual for your inverter make and model.

The ground connection on the metal box of the inverter is typically frame ground for the 120 volt side. It should be the same gauge as the system ground on the 120 volt output. It trips circuit breaker or blows a fuse when certain wiring malfunctions occur.

However, some inverters are designed to also frame ground the 12 volt side and larger gauge is required.
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Old 10-07-2021, 09:47 AM   #11
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Too bad I didn't invest in copper futures. This is a calculation for a 3000 watt inverter, running at 12.8 volts (fully charged bank.) Roughly 250 amps draw, inverter located 5 feet from the battery bank (5+5 = 10 foot run). as you can see, 4/0 to 2/0 buys .07 volts at peak draw, or .5%. Hardly worth it.
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Old 10-07-2021, 10:07 AM   #12
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Quote:
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Too bad I didn't invest in copper futures. This is a calculation for a 3000 watt inverter, running at 12.8 volts (fully charged bank.) Roughly 250 amps draw, inverter located 5 feet from the battery bank (5+5 = 10 foot run). as you can see, 4/0 to 2/0 buys .07 volts at peak draw, or .5%. Hardly worth it.

Line loss is only one consideration, keep in mind that if you have 250a sustained current that a 2/0 cable is going to run much hotter and in fact hotter than what most 2/0 cables are rated for. I don't have the specifications in front of me, but the 2/0 cable would likely run 225+ degrees or more (very hot) at a sustained 250a where the 4/0 cable would run much cooler (perhaps 75f degrees cooler, although I don't have the specs to check this right now to tell exactly how much cooler, but for sure a lot cooler with the larger conductor). ~CA
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Old 10-07-2021, 10:51 AM   #13
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The ground I refer to connects the aluminum enclosure to the trailer chassis.

The AC lines all have 3-wire connectors.

The Victron manual does not discuss the ground.
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Old 10-07-2021, 10:57 AM   #14
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I suggest a 6 AWG solid copper grounding conductor, as short as possible. Chances are the grounding connection on the inverter would have to be modified to take anything larger than that.

Equipment grounding conductor table
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