question

taddy avatar image
taddy asked

Earthing and power feed on this system...?

Intention…

My plan is to have a solar system with pylon Li batteries supplying 6 lower powered circuits in the house - lights and some socket ring circuits - with the grid charging batteries when needed. The grid will also permanently supply my higher-powered circuits such as the shower and electric cooker (the solar system will not be involved here).

Equipment

I have 3x 3.5kW pylon batteries, Multiplus II 5kw, 9 x 455W panels in 3 paralleled strings of 3 panels, 250/100 smart soar MPPT , lynx distributer and cerbo gx.

I have attached my wiring diagWiring plus poss consumer unit layout 2.pdfram for the solar system (p1) and for the consumer unit (p2). I need to get an electrician to check and wire this but just have a few questions for you guys if you can help…

Questions…

1.Is the grounding/earthing safe and correct?

2.With this set up is there any way in which I might be putting power back into the grid or is it just one way? If I am not putting anything into the grid do I still need to fill out the G98/99 applications?

3.How long could my cable runs be consumer unit to the inverter charger? I am still unsure as to whether to have the solar gear in the garage or a different room in the house or even in the loft…

Apologies if some of these questions are very basic!

wiring
wiring-plus-poss-consumer-unit-layout-2.pdf (145.2 KiB)
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4 Answers
sharpener avatar image
sharpener answered ·

1. You don't seem to have an independent earth connection to the cases of the Pylontechs, otherwise it seems OK to me. It is allowable to connect your earth electrode to the incoming PME earth as you have done but there are also some advantages to converting your system to TT earthing and not using it (the PME earth). Too complex to discuss here, maybe Wiring Unlimited has further guidance, it is certainly worth reading anyway.

2. Yes, as discussed in your earlier thread https://community.victronenergy.com/questions/156610/ac-on-the-inverter-charger-post-rcd.html, with this setup the Multi can export (and at more than the 16A limit), even if you don't intend to, so because of this you will need to make an application to the DNO, who may impose restrictions e.g. 3.68kW max export and 3.68kW max inverter power.

3. Any reasonable length, you need to size the cable for voltage drop and check that the various impedance limits for fault protection are not exceeded. If you regard it as a power device then 5% voltage drop is permissible but IMHO it would be better to size the cables for 3% or less, in line with the limits for PV panel cables and lighting circuits and remembering that the voltage drop % is also a % efficiency loss.

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taddy avatar image taddy commented ·
Thanks again Sharpener. WRT q2 can you explain the path by which the multi feeds power back into the grid as atm I can't quite see it. Is it via the AC IN on the multi?
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ponzoa avatar image ponzoa taddy commented ·
Correct, via ACIn.
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ponzoa avatar image
ponzoa answered ·

Don't forget you also need to earth the AC in and AC Out connections in the inverter, apart from the batteries as previously mentioned. You won't be able to double your cables from the batteries to the Lynx but 3 US3000C on a single cable set is fine and you won't have issues. If you do want to double your cables, you'll have to run the batteries individually to the Lynx or get a fourth battery and run the batteries in pairs to the Lynx. You'll need an extra Lynx distributor for that as they have 4 fused connects per Lynx Distributor.


Note: Unless you install can ET112 meter at the feed in from the grid, your shower, cooker and sock16/20 won't be powered by your solar and baterías. If you do install that meter, you can use your solar and batteries for the entire load although you'll only protect the other half of your switchboard in case of a power outage.

The ET112 is connected to the Cerbo GX USB connecter.

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sharpener avatar image sharpener commented ·
I think the OP's intention is not to power the high current loads from the batteries. But if the Multi is configured in ESS to allow export from the DC side the solar PV will nonetheless help with these loads even without the ET112 (except as you say in a power cut).


If limited to 3.7kW this should prove acceptable to the DNO and is only slightly less than the 4kW continuous rating of the Multi anyway.


BTW @Taddy I have got a full-size cooker behind my Multi 5k and it hasn't ever tripped the 50A breaker - but I wouldn't like to have an electric shower as well. So you might get away with having the cooker on the AC-Out side, then you could cook (at least up to 4.4kW total) in a power cut.


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daza avatar image daza sharpener commented ·
Now this is a mind field diversity calculations I’ve given up and think a clamp is a better indicator of the amps you use, but yes an electric shower and cooker will probably run together at some point. When I started to work mine out my cooker only used 19.8amps Max and that’s only at the point of heating the elements.


for the Earth thing are you talking about the relayed earth? I just saw this as a mind field as you still need your own so might as well just have the rod all the time.

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taddy avatar image taddy sharpener commented ·
That is great news. I'll prob shift the cooker over to the solar supplied side then. I was thinking about getting a lower-powered and more efficient cooker anyway.


So from what you guys are saying, if the batteries are full and the inverter is satisfying any load demands on the AC OUT, if there is still any excess power coming in off the PVs then that will be fed into the grid via the ACIN cabling (and this is ESS mode)....? Presumably if it doesn do that then the excess would have to dissipate as heat and that is not healthy for anything.
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taddy avatar image taddy sharpener commented ·

Finally getting close to actually putting this thing together and just going over a few things and went back to this post. Is there any advantage in having an ET112 in my set up? [My proposed set up is having lower power loads on the AC-OUT of the multi and higher ones on the AC-IN side].

On p4 of Victron's ESS Design and Installation Manual it says...

"For a full or partial grid-parallel installation an Energy Meter can be installed in the main distribution panel between the grid and the installation.
A grid meter is not required where there are no AC renewable-energy source(s) and also no AC load(s) present on the
the input side of the Multi/Quattro system (i.e. where all such sources and loads are on the output side of the Multi/Quattro
system).
If there is any AC renewable energy source or any AC load between the grid connection point and the input side of the Multi/ Quattro system, incorrect results will be calculated and recorded by the GX unless a grid meter is installed and enabled.
In particular, without a grid meter:
• When renewable energy is being provided on the input side, the grid value will be wrong (too low/negative); and
• The AC Load value shown will be too low (and will show zero where there is a surplus of renewable energy).
Both issues are resolved by installing a grid meter. "

So I read this as: if I don't have the ET112 then the readings on the GX will be incorrect. [But in theory everything would actually still work in terms of excess PV power or battery power (when in self-consumption) going to loads on the AC-IN side?

Thanks for all your help so far!

Tom


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taddy avatar image taddy commented ·
Thanks for the answer. It's strange because the company that supplied me this kit checked my diagram which originally only had one positive and one negative cable from the batteries to the lynx and they said I needed to double up (apparently two cable-battery sets are in the kit for this purpose but I haven't received these or the batteries yet). The mutliplus documentation seems to recommend 70mm2 for the 48/5000/70 which is even bigger than 2x25mm2 pylon cables! Is it that 2 lugs wouldn't fit on the lynx terminals?

Also I thought that with the multiplus I thought the chassis ground is continuous with the ACIN and ACOUT ground so wouldn't earth cables on ACIN and OUT just be going to the same place anyway? Sorry, if my questions are very basic!


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sharpener avatar image sharpener taddy commented ·
Yes, one earth cable is sufficient.


Can't help much with the battery cables as my Pylon Force L2 has only a single cable from the BMS for up to 4 x 3.55kWh modules (I have two). This cable is rated at 100A (AFAIR this is limited by the temperature rating of the plug-in connectors). The cable gets slightly warm to the touch with 74A so I would guess it's good for 100A which is the max o/p from your MPPT anyway.


There are 2 x 2kW inverters between my panels and the AC-Out if that is what you were querying. So they work in a power cut, the neat bit is if they are generating too much for the Multi to cope with it shuts them down by raising the system frequency slightly, then it runs off battery for 5 mins and tries again.

Have at last found the notes I was looking for about ovens:

The smallest I have been able to find that claims to take a 10in pizza is this, https://www.amazon.co.uk/dp/B09HKBKL4P 1400 W (presumably 700W grill only), there is a slightly larger one in black also 1400W which one reviewer says is what you actually need for a 10in pizza. Air frying capability as well would be good to have but they are bigger and use even more power. So no good answer.

The smallest overall is this https://www.amazon.co.uk/dp/B09J4G35X9, only 650W, it will do fish and chips or one ready meal or maybe two slices of pizza. The reviews are a bit mixed (though better than the equivalent Netta or Belaco product) so might be worth a punt at £40! That would buy 120kWh at peak rate even at present prices, so saving say 500W x 1/2 hour will pay for itself in 480 meals(!)
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ponzoa avatar image ponzoa taddy commented ·
For up to 3 batteries, the supplied cables by Pylontech are fine. If you get more batteries, you'll have to run more of these cables to your lynx distributor where you fuse your battery runs. From the Lynx to the Multi you can use the larger cables so you have room to grow your battery bank. Your MPPT should also go to your Lynx. If you need more than 4 connections to your Lynx, you can add another one so make sure that when you install the lynx distributor, you leave room to add another one.


Good luck.

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taddy avatar image taddy commented ·
Hi Ponzoa, Just about to install my system and coming back to the battery wiring on the pylons. My supplier is saying that I must double the cables from the bank of 3 pylons to the Lynx. I'm thinking they mean that you could have one positive from battery 1 (the master/top battery in the stack) and one positive from battery 3 (the bottom one in the stack), and the same with the negative. Would that work?
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ponzoa avatar image ponzoa taddy commented ·
No don't do that. Positive on one side and negative on the other please. Well, only if you like balanced trouble free batteries.


The pylontech cables are rated at 130A so 130A @ 48V is some 6240W which is more that what your inverter charger si arted at. One set of batteries os fine. If you get more batteries, then get more cables. 3 x US3000C is fine on one set (the limit actually).

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ahtrimble avatar image
ahtrimble answered ·

Do you have the DC negative grounded? My battery manufacturer said not to.

Also, I ground my PVs separately for lightening strikes. 3x8' rods, 10' apart, bonded with 6AWG that is also buried.

And here our earth is very dry, somewhat rocky. I have 3 x 8' ground rods, 10' apart, bonded with 6AWG bare copper (also buried).

Does your Gerbo need to also have an equipment ground?

I notice your battery cases are not equipment grounded.

I didn't see a AC ground wire on your inverter. My Quattro has a ground right next to the AC out.

Are you bonding ground and neutral in the inverter or at the main breaker panel?

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taddy avatar image taddy commented ·
Not sure about grounding the negative on the battery. I don't believe it is desirable but I can't remember the reasoning!
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ahtrimble avatar image ahtrimble taddy commented ·
Yeah, I've seen different opinions on this. So I went straight to the battery manufacturer and they do not ground the negative side of the battery at any point in the system. Good enough reasoning for me :)
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taddy avatar image taddy ahtrimble commented ·
Thanks dude- I'll think I'll do the same and check with the battery supplier
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taddy avatar image taddy commented ·

Hi. Yes I've modified the plan a bit since the original post. So apparently the pylon battery cases need to be grounded and the MPPT. Not sure about the Cerbo - I'll have to check that one! There is a ground connection on the Multiplus but I'm also going to have the grounds on the AC in and AC out which wasn't in the original diagram.

WRT this question... "Are you bonding ground and neutral in the inverter or at the main breaker panel?"... victron inverter chargers have an internal ground relay (see p59-60 in Wiring Unlimited) so when in charger mode the grid AC power supply provides the ground-neutral link (MEN link). When its in inverter mode, the multi makes the link. So I think I shouldn't make an additional MEN link as this will confuse that system. Please anyone correct me if I have this wrong.

WRT grounding the PV array the solar electrician who is helping me advised against it.

We don't get very much lightning in the this part of the world.


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ahtrimble avatar image ahtrimble taddy commented ·

Ground/neutral bond should be as close to the production source as possible. In my case I am not grid tied, I do run a genset (on AC1 in or completly by-passing the entire solar system side) occasionally...like 1 - 2 times per year. The genset floats so I do the ground/neutral bond at the main breaker panel. Yes, I unchecked the "ground relay" setting in my Quattros.

I have never heard of not grounding the PV array, but that doesn't mean I am right. I would want any surge against the panels or stray voltage to go directly to earth ground...and utilize a SPD as well. Also, code here requires it...if that means anything. Also, my close friend who has been doing solar for 30 years, his own company and a licensed electrician, made sure I had grounded my PV array correctly. But, I have been found guilty of over-engineering before :)


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taddy avatar image taddy ahtrimble commented ·
Yeah, it's weird. I haven't been in this very long but I've noticed some radically different opinions on various issues. The guy who advised me not to ground the panels has also been doing it for years and has all the qualifications.
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ahtrimble avatar image ahtrimble taddy commented ·
So what does he say about surges/strikes/CME's and even stray voltage...as in what happens to all that energy?

I would be interested in what he has to say.


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taddy avatar image taddy ahtrimble commented ·
I'll ask him next time I see him but just looking at all the houses in the street that have solar panels and none seem to have grounding on the PV.
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daza avatar image
daza answered ·

Right this is a mine field of a topic, So i done a dive into TNC-S with PME as that what mine is. And the issue is the neutral tired to earth bond that goes when the house is in island mode. The issue here is yes you can put an earth rod in the ground and make a TT system but its very hard to keep it a TT system looking at some of the requirements it has to be about 5meters plus from the incoming as to not feed connect to the grids earth again, next is that in the UK all under ground pipes should be bonded which means we've just done all that work and still got a TNC-S system also all metal pipes feed to neighbouring properties are also earthed which feeds back to you which keeps it a TNC-S system. PS it is essential that all metal pipes entering the property be bonded to earth for everyone in or outside that house coming into contact with metal pipes are safe.

Glad i replaced my last metal pipe with plastic so not tired to earth meaning i just need to keep away form the coming mains and any metal work. I see a lot of people are looking at the earth bonding relay but really don't see the point in this, yes the resistance is a lot lower on the DNO due to the PME but if the relay contacts get stuck you have a problem. I would rather sink 4 to 5 rods deep get a good earth obviously tested to make sure its within the 200ohms or better still 100ohms or lower.

Last thought on why this isn't done to much in the UK might because the property might not have a garden in order to keep 5 plus meters away from cables metal pipes to take and earth rod. Lastly i have only seen one SPD done and it was by Oval renewables which i think is now a requirement for solar. On the AC the 18th edition has made it pretty much mandatory for an AC SPD.

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