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flamegrilledmatt avatar image
flamegrilledmatt asked

AC Cable sizing for Multiplus II 48/5000/230

Speccing out a home battery storage system using a multiplus II 48/5000 230v. Looking at the maximum AC in - this is rated at 50amps (11500va), so could be run in 10mm2 cabling, however if I've understood correctly the AC out side with powerassist could potentially deliver the grid feed in of 11500va plus a further 5000va from the inverter. So at 16500va (or 16.5kW) you would need 16mm2 cabling to feed back to the load side (consumer unit) - using online cable size calculator. Looking at the spec sheet the inverter only has 13mm2 terminals? So here in the UK, it's either 10mm or 16mm. 10mm is under-specced and 16mm won't fit in the inverters terminals. What am I missing?

Multiplus-IIgridac
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Alexandra avatar image
Alexandra answered ·

@flamegrilledmatt

The maximum transfer to or from grid is 50A. It is in the technical specs for the unit.

It does not power assist to grid, but will power assist loads. But also wont hold the peak for long enough to heat cables.

See the tech specs in the manual here.

If you are planning a system those big loads get a bigger inverter.


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flamegrilledmatt avatar image flamegrilledmatt commented ·

Hi Alexandra and thankyou for the quick response.

I was not suggesting power assisting to the grid, hence the 50amp input rating, however a discussion on here regarding the 3000VA.... https://community.victronenergy.com/questions/86527/is-multiplus-ii-300048v-35-capable-of-transferring.html

Would suggest that in that case it can take the 32amp input and "add" a further 13amps to the AC output?

This is also mentioned in the manual from Victrons own website?

screenshot.png

I would therefore presume that the 5000VA could take a 50amp input and "add" a further 21.7amps giving me a total of 71.7amps.


As the tech specs and manual seem to contradict each other, please advise?

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Alexandra avatar image Alexandra ♦ flamegrilledmatt commented ·

Depending on derating due to heat, grid voltage etc. And batteries.

Also if you have ESS or not.


There is a settable factor that can be applied if not using ESS to add power to the incoming amp limit. This factor if not set up correctly can cause overloads though. If you search power assist you will find posts on it. You ca. Also goodle victrons power assist there is a white paper on it.

A good setup can add its full nominal inverting power to the incoming current limit.

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steegergrid avatar image
steegergrid answered ·

Use 10mm² cable for an ESS System it is fine. Everyone does. In Germany at least all electrical cabinets are just wired in 10mm² and are rated for 63amp

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Alexandra avatar image Alexandra ♦ commented ·
Especially if it is the flex or fine/many strand not the hard drawn stuff.
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flamegrilledmatt avatar image
flamegrilledmatt answered ·

So to clarify, 10mm will be fine, as no more than 50amp can pass into or out of the unit. Would this also apply in single leg config, only wiring the AC-In. Seen a youtube video lately that suggests you only need wire the AC-In as this will work both ways, if that makes sense and therfore I presume a 50amp RCD on the 10mm cable would work with feeding the charger and when it is inverting mode. Apologies for all the questions, just need to get it clear in my head!!

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dancrompton avatar image
dancrompton answered ·

I have the same concerns. I've literally just seen the 13mm limit now, assumed 16mm would fit easily.


My problem is the main CU is 5 metres away from my installation. I don't feel comfortable using 10mm for such a long run. I think I'll install a small CU with 2 x 63a 2 pole isolators near the inverter and feed 16mm from the main CU to that. I'll then just have a short run of less than 1 metre in 10mm. It'll be more work and expense but I will sleep easier at night. It also future proofs me should I upgrade to a larger Inverter at some point.

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flamegrilledmatt avatar image
flamegrilledmatt answered ·

Hi Dan, they certainly don't make it easy do they! Another thing I have found out since asking this question is that if you're in the UK and putting in a G99 application, that the multiplus isn't compliant at the moment. I ended up putting in an application for a 6kW Solis and just had it approved, hats off to UKPN - done in 3 weeks, but am holding off purchasing because I really like the Victron gear (even if it means I have to re-submit another G99 because inverter has changed, waiting to hear back on that one), but if it's not sorted soon, then Solis here I come.

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dancrompton avatar image dancrompton commented ·

I know what you mean. There's so much conflicting information out there it's hard to know what to believe. I'm convinced I'd read somewhere that 63A MCBs were required for both AC-OUTs on a 48/5000. And in my experience 63A = 16mm cable. Minimum. If I can find it I'll post a link.

I haven't even begun to look at G99 Certification yet, probably putting the horse before the cart, but my project is far from standard and likely wouldn't pass anyway. My panels aren't on my property, they are on a neighbours barn, installed by myself. So I suspect I may fall at the first hurdle.

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dancrompton avatar image dancrompton commented ·

@flamegrilledmatt I finally found it! The info in this question is what threw me.


https://community.victronenergy.com/questions/83375/multiplus-2-current-limit-on-throughput.html


This suggests -: AC-OUT-1: 50A + 21A = 71A

AC-OUT-2: 50A


It checks out. The installation documentation for the MP2 install reads -:

The AC output cable can be connected directly to the terminal block 'AC-out'. From left to right: "N" (neutral), "PE" (earth) and "L" (phase) With its PowerAssist feature the Multi can add up to 3kVA (that is 3000 / 230 = 13A) to the output during periods of peak power requirement. Together with a maximum input current of 32A this means that the output can supply up to 32 + 13 = 45 A. An earth leakage circuit breaker and a fuse or circuit breaker rated to support the expected load must be included in series with the output, and cable cross-section must be sized accordingly.


This is referring to the 48/3000, but when you take into account the 48/5000's 50A input current and 5kVA (that is 5000 / 230 = 21.7A) it does indeed look like the AC-OUT is capable of 71.7A.

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flamegrilledmatt avatar image flamegrilledmatt dancrompton commented ·

@danmc I'm still building the battery at the moment, inverters on the wall but leaving the AC cabling etc to a sparky booked in for beginning of March as need his EIC sheet to complete the G99 application. Long story, but was prepared to do it myself, even prepared to sit a C&G course etc, but local building control won't have it, won't even inspect and sign off as you need to be member of the competent person schemes.

But as I understand it then, I'm going to need a 50amp MCB, with a suitable isolator on the AC-In, and a 100amp MCB (next closest size after 63amps) on the AC-Out to allow for the 71.7amps potential max?

This surely further raises the question again then on cable sizing as pushing 71.7amps through 10mm cable I would have though is pushing it and even taking on board @delf67 comment about type 4 cable, the cable with a 100amp MCB isn't protected properly??

PS: Like the avatar, Karl "pilko-pants" Pilkington - absolute legend! "What were them things in Gremlins called?"

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dancrompton avatar image dancrompton flamegrilledmatt commented ·

Despite the datasheet saying 13mm, 16mm TNE does indeed fit. I tried it myself last night. Whether it is supported/recommended is another thing entirely.


I'm toying with the idea of sizing for a 48/5000, but just fitting a 48/3000 and getting G98 certified once they are ENA approved. I have no interest in feeding back to the grid at current rates, and as I've done literally everything myself from fitting the panels to putting all the AC equipment in place (With guidance/sign off from my brother in law who is an electrician, but not MCS certified) I very much doubt I would be able to get G99 certified anyway. At least this way if they relax the rules at some point I can swap the 48/3000 out for a 48/5000 or even a Multi RS 6000 if they ever update it to support ESS mode without too much trouble.

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Craig Chamberlain avatar image Craig Chamberlain dancrompton commented ·
@danmc Another FYI, I just received G99 approval from SP Energy Networks, who are normally pretty strict, to go ahead with my Multiplus-II 48/5000/70-50 commissioning. I too have installed everything myself since I live in Scotland and we're allowed to do that as long as we do it to the regs. So might still be worth going for the 5000VA model from the start.


Regarding the use of 16mm cable when the manufacturer's spec says maximum of 13mm, following manufacturer's specifications is an important part of BS7671 so I'd say you should abide by the spec unless you have a strong case for using engineering judgement to exceed it. For example if you found the data sheet for the actual terminals used and they said 16mm capacity.

FWIW, I'm using 10mm singles (actually 10mm blue and brown cable stripped from T&E but I'm using 10mm CPC cables instead of the 4mm(?) CPC from the T&E. Probably not necessary to have the full 10mm for CPCs but there you go... I also have a 50A MCB from my primary DB to the 63A lockable AC isolator for the MP-II. I went with MCB instead of RCBO because I couldn't find a time delayed RCBO for my Fusebox DB and didn't want to mix brands. But again, the cabling goes direct from DB to conduit to DB with nothing hidden in walls etc so I believe this is compliant.

I am tempted to upgrade the 10mm to tri-rated cable partly as it's nicer to work with but also has higher current specs. But for such short runs as singles inside 75x75mm conduit, I think 10mm will be just fine. It's not as if the DB on AC-Out1 has any particularly high loads in it. I suppose you could use 10mm + 2.5mm cables in parallel to get close to the 13mm max but that just seems more likely to cause problems due to having two wires in the terminal instead of one.

Hope this helps.

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dancrompton avatar image dancrompton Craig Chamberlain commented ·

Sorry just seen your reply. Congrats. I'll have to take a closer look at where the land lies in England. Thanks.


I think the 13mm is a typo after looking at it again. I'm kicking myself I didn't pick up on it the first time. it reads "Screw terminals 13 mm² (6 AWG)" 6 AWG = 16MM.





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flamegrilledmatt avatar image flamegrilledmatt dancrompton commented ·
Just an FYI, UK Power Networks accepted my G99 about 2 weeks ago, despite the ENA register still saying "awaiting further information" for the MP-II 48/5000/70, I did detail that a ET112 energy meter would be installed as well (which it will by the sparky). Luck of the draw I suppose.
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flamegrilledmatt avatar image flamegrilledmatt flamegrilledmatt commented ·
Should add that the Solis 6kW went in first, then submitted another G99 stating exactly the same but instead installing the Multiplus instead of the Solis. Approved next day!
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delf67 avatar image
delf67 answered ·

All cables are NOT equal. eg BS6195 type 4; 10mm is rated at 81A single phase AC.

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dancrompton avatar image dancrompton commented ·

Correct me if i'm wrong but that only applies to single core doesn't it, not multicore (Twin & Earth)?


https://elandcables.com/media/38271/coil-end-lead-type-4-bs-6195-cable.pdf

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delf67 avatar image delf67 dancrompton commented ·
So run singles in flexi conduit. You don't have to use multicore.
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dancrompton avatar image dancrompton delf67 commented ·
That would certainly be an option for a relatively short cable run.
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