Victron MultiPlus II / MultiPlus II 2x120V in a home setting

Per the Spec Sheet both units are designed as 120V inverters utilizing battery power when AC Power is loss. Cool, get that.

Both units have a 240V pass thru mode (requires (2) MultiPlus II or (1) MultiPlus II 2x120V if I'm reading it right) where 50amps of 240V power is available on the output side if provided on the input side. The 240V power drops when AC goes away. OK, nothing in === nothing out.

I'm guessing this has value in boat or RV situations, but does it buy me anything in a home situation? Wouldn't I just wire my 240V needs into my non-critical panel and use the 120V single pole breakers in the critical panel?

Would the 2x120V simplify installation? e.g. Run a 50Amp 240V as AC In with L1 and L2 being hot and N being neutral, then feeding L1 Out to one side of a panel, and L2 Out to the other side (sharing the common neutral) and then being careful to only put computers on the L1 Out side of the panel? Lights, hand tool battery chargers, and other things that could handle a 40ms blink being wired to the other side? That would yield 50amp on both sides of the critical panel right? (vs. using L1#1 on one side and L1#2 on the other, sharing 50amps between them???)

My existing grid panel only has (3) 240V breakers in it. Thinking perhaps the easiest conversion may be to move my main to the smallest 200amp panel I can find, rewire those (3) breakers into it, and add a 50amp breaker for a Multiplus II 2x120V? Speaking of breakers, the Multiplus is rated at 50A per leg, but the 2x120V is only 5500VA surge, so about 45amps total. Right?

KevinC_63559 said:

Would the 2x120V simplify installation? e.g. Run a 50Amp 240V as AC In with L1 and L2 being hot and N being neutral, then feeding L1 Out to one side of a panel, and L2 Out to the other side (sharing the common neutral) and then being careful to only put computers on the L1 Out side of the panel? Lights, hand tool battery chargers, and other things that could handle a 40ms blink being wired to the other side? That would yield 50amp on both sides of the critical panel right? (vs. using L1#1 on one side and L1#2 on the other, sharing 50amps between them???)

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You may be aware but the legs are alternated as you go down the breaker panel, not one side being L1 and the other being L2

Brucey said:

You may be aware but the legs are alternated as you go down the breaker panel, not one side being L1 and the other being L2

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Yeah, over-simplification on my part. Sorry.

Spent more time reading and sorting info in my head. Currently under the impression for my usage, there is little need for the 120V versions. So can close this thread.

As per the literature the 2x120 unit will provide 120v to both output legs in the event of a single phase input or during inverter use

Both legs of your panel would receive 120v in all conditions but 240v is only available with a 240v shore power source.

Basically letting you seamlessly power up everything in the house other than high current 240v loads. So great for use as a backup system, not what you want for full time use

Thanks. Alas this is an old post and my understanding has grown since then. Here is my current thread: Journey

KevinC_63559 said:

Thanks. Alas this is an old post and my understanding has grown since then. Here is my current thread: Journey

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Sorry didn’t see the date!

Ykdave said:

Sorry didn’t see the date!

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No worries. You actually made me want to double check one presumption, so thanks.

What does something like a 240vac drier do when it switches to inverter mode? Just not turn on, or run at 120vac with reduced power?

Nothing good. Most 240v appliances in NA and CA are expecting split phase power. You can configure a pair on mpii 3000s or 5000s to provide that 240v split phase. Note this is NOT the same as EU units that do 230v single phase.

If a 2x120 is inverting to power a home's 120/240V split phase panel, all 240V devices will see 0V and do absolutely nothing, nor will they be damaged.

sunshine_eggo said:

If a 2x120 is inverting to power a home's 120/240V split phase panel, all 240V devices will see 0V and do absolutely nothing, nor will they be damaged.

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So, presumably, the only risk then is if you have any of those 120vac outlets in your house that are wired in that slightly less common way, where they are using both legs.. I don't remember what it's called. Maybe one of the many electricians on here can remind me. Perhaps they can also remind me what will happen to anything on those outlets in this situation.

cs1234 said:

So, presumably, the only risk then is if you have any of those 120vac outlets in your house that are wired in that slightly less common way, where they are using both legs.. I don't remember what it's called. Maybe one of the many electricians on here can remind me. Perhaps they can also remind me what will happen to anything on those outlets in this situation.

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Any 240v wired appliances will just cease to function as they will see zero volts like mentioned above

Regular 120v sockets that are double fed whether off of one leg or both will still continue to function as normal

There is a potential issue with the 2x120 on 120V circuits:

If you have any Multiwire Branch Circuits (MWBC) in your house, you risk overloading its neutral conductor and starting a fire.
This is because the cheap-ass electrician decided to save a run of wire when they did the install.
The MWBC is a 3-conductor + ground cable, and the design counts on the two hot legs to cancel each other out with the neutral.
If both legs are the same (from the 2x120), there will be no cancelling out and the neutral can carry twice the intended current.

For example, my house has the dishwasher on one leg and the kitchen lights on the other. Idiots.

Had that same thing in my previous house built in 2004. Bedrooms were split via MWBC. Friggen arc-fault MWBC breaker were like $375... Idiots indeed, they were outlawed a year or two after my house was built in our area.

KevinC_63559 said:

Friggen arc-fault MWBC breaker were like $375... Idiots

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Wow, never knew they existed.

Back in the 90s added some outdoor lights to the kitchen light circuit, so I wanted a GFCI breaker for the circuit.
Wired it up, and found out real fast that running the dishwasher tripped the breaker.
Then I figured out why, so now I like to spread the bad news about MWBCs.
Live and learn.

What's the easiest way to tell if you have any MWBCs?

cs1234 said:

What's the easiest way to tell if you have any MWBCs?

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In the breaker box (load panel, load center, whatever you want to call it):

Look for two regular single-pole breakers typically next to each other (not the little tandem ones, and not the two-pole 240v ones), which go to a single cable with red, black, white, and ground conductors. The red and black wire will go to the two breakers, but there is only one neutral wire.
Depending how neatly things have been done this may be difficult to see.
Start by looking for red wires that go to regular 120v single-pole breakers.

Also, I am not an electrician.