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jambaloney avatar image
jambaloney asked

Can I use a double pole 240V 50 amp breaker with a Multiplus 12|3000|120?

I am building a small battery backup system for my home in the woods. I have 4 panels and 4 batteries no problem. I am upgrading my Inverter form a 3 prong outlet Hardware store inverter to a Multiplus 12|3000|120 which I have purchased. I also have a proper strand of high quality RV 6/4 wire for AC out #1.

I want to wire it to a small load center - I have this small 2 slot box from Siemens WITHOUT a main breaker:

Siemens 4/8 Circuit 100A 120/240V Loadcentre | The Home Depot Canada

Victron specifies a 50 Amp breaker for the AC out #1. Can I use this double pole 50 Amp 240V for the red and black wires coming IN to the panel?

Q250 50-Amp Double Pole Type QP Circuit Breaker : Amazon.ca: Tools & Home Improvement

I will lose 1/2 the space but can use space saving breakers in the other 2 slots. If this works I can always upgrade the panel later but for this installation - backup vital power, I don't think I will need it. If I chose to go full off-grid I will build a separate 48 V system later.


I know that the specifications for all of this is very particular (wire sizes etc.) and I have been on point thus far. But I am stuck here - all breaker boxes etc. seem to be RV specific and i won't ever be using the DC option etc. I want standard electrical infrastructure after the inverter.


Thank you in advance for your help - cheers!


Multiplus-II
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4 Answers
chrigu avatar image
chrigu answered ·

Heavily depends on your local regulations. I could not use this breaker. I would have to match the breakers amperage to the feeding device, in this case 25A (3000VA/120V) Reason is, a 50A breaker would never trip at 30A, but the Multiplus would already be overloaded. Sure theres electronics that protect the multiplus, but that doesnt count for the officials. Its rated at 3000VA, thats what counts.

Furhter, i can only use a simple breaker if theres only one single socket behind the inverter. As soon as there are multiple sockets, or just a power strip, i need to use an RCD or RCBO. This in turn means that it also needs proper earthing.

So check your local regulations regarding installations behind an inverter or in island operation.

I guess you are using the split-phase 120V type? Read the manual carefully, it does not actually provide a split phase. It provides the same 120V leg on both phases when inverting.

(I guess the 50A specification is due to usage on the grid. The internal relay can switch 50A, so there must be a breaker of max 50A)

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Justin Cook avatar image
Justin Cook answered ·

...as another note, make sure you purchased the correct MultiPlus; the MultiPlus 12/3kVA/120 doesn't have 4-wire input at all, it's strictly single-phase. If you're intending to use 4-wire input you'd need the MultiPlus-II 12/3kVA 2x120 model. https://www.victronenergy.com/inverters-chargers/multiplus-ii-2x-120v

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jambaloney avatar image
jambaloney answered ·

Sorry - the links did not work as expected:

50 Amp breaker

Small Siemens Panel

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jambaloney avatar image
jambaloney answered ·

Thank you both for the information - VERY helpful. I do indeed have the 2x120v model with the 4 wire output so I can use the 2 phase breaker... i "think".... apparently this is called "backfeeding" and is done a lot with generators.


However I was not reading the output for the 2x120 so now it recommends a 75 A breaker:

1724875521969.png


Should I try and get an outside mount AC 75 amp breaker (marine or rail type) and install that before the wires going into the panel?

Thanks again!



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