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logic28 avatar image
logic28 asked

Multiplus II Grounding

There is a slight confusion in my mind, I hear that the ground cable must be at least one size down from the battery cables and that the same applies to the inverter ground cable.

Victron Wiring Unlimited clearly specifies that the Grounding cable must be able to carry at least the same current as the battery fuse rating (I’m compliant with that) but does not specify the size of the inverter ground cable. Also, the inverter ground connection does not offer many options over a certain size because it only carries a 6mm stud/nut hence not indicating the need for large lugs/wire

Multiplus-II
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2 Answers
Alexandra avatar image
Alexandra answered ·

@Logic28

It is confusing. And it also depends on what you are grounding and from where and is the install mobile or fixed. And then of course local regulations.

If you are grounding the MP case to the AC ground, then use larger than the AC gauge you are using so it can carry full current. But also don't forget you are grounding through the normal wiring which is also usually the same size gauge as incoming. This may not be sufficient.

So really more details about your install would be helpful here.

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logic28 avatar image logic28 commented ·

Thank you for the reply, this is my setup (off-grid/grid assisted only for charging):

1 x 6.2kWh ground mount PV 20m away from solar shed

1 x 2.1kWh PV over the solar shed roof

1 x Solar shed containing Batteries, Power in, Distributor, Linx Shunt, I x Multi II inverter, 2 x MPPTs Distributor and Generator.

The grid assist comes from the house and I'll only be using it for emergency battery charging.

Hope this explains better.


Victron Wiring Unlimited clearly states that AC and DC are in isolation so I would assume that the YouTuber was incorrect in instructing to install the same gauge ground for both the battery and the inverter.

My feelings were leading toward using the same gauge of the incoming grid power or perhaps a step more as you rightly said.

But that leads to the next very important question posted here

https://community.victronenergy.com/questions/218447/grounding-of-grid-grid-assisted.html


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Alexandra avatar image Alexandra ♦ logic28 commented ·

You should be ok then. If you have used big gauge wiring then upsizing or adding extra for the grounding is probably not necessary.

Battery grounding for BMS batteries is usually just for the electronics in there, for stability and people protection. Not fault current from the battery. That should blow DC fuses.

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ejrossouw avatar image ejrossouw logic28 commented ·
While you check the latest regs, note that UK regulations now require systems that can operate in island mode to have a dedicated ground rod for the system installed given in e.g. a TNCS installation the E & N are combined in a single conductor to your property and were it to be severed, you would lose the E.
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mvas avatar image
mvas answered ·

Your local electrical codes dictate the size of the wires. Not Victron. There is no confusion.

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logic28 avatar image logic28 commented ·

Thanks,

This system is not going to be subject to inspections but I will still check the British Standard 7671 however, I doubt that it will tell me anything about the internal wiring of an Off Grid system of this nature.

All the wiring from and to the garage (where the energy will be used) is well above the local requirements as I always tend to overengineer everything I build


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Alexandra avatar image Alexandra ♦ logic28 commented ·
Battery grounding has different needs. Most times it is just a small wire and that is usually grounding for the bms.


If you look at Pylontec kits online you will see the size there. Most battery manuals give a recommendation though. And it will be grounded to the AC side anyway.

Grounding the negative terminal of the battery is a different subject. We don't usually do that for fixed installs there is a whole debate/discussion over that.


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