question

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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6 Answers
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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screenshot.png (283.2 KiB)
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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danmc avatar image
danmc 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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danmc avatar image danmc 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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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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danmc avatar image danmc 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 danmc commented ·
So run singles in flexi conduit. You don't have to use multicore.
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danmc avatar image danmc delf67 commented ·
That would certainly be an option for a relatively short cable run.
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