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Just installed a new multiplus ii 12v on a 50amp RV. Shore power coming in has 2 leads, neutral and ground. Then on the output I have same 4 wires that go to panel. When on inverter mode it outputs 240v (2x120v) perfectly. But when I’m using shore power and not invertering it’s only outputting 120v on one leg and the second leg is dead. Any ideas?
If you are talking about the Multiplus II 2x120 model, then you should be seeing 120 volts on both legs at it's AC output while inverting, BUT those outputs will be IN PHASE (0 volts between them). This is because the unit only has one 120v inverter.
When shore power is present, L1 functions like other Multis and Quattros and will do power assist. L2 however is passed through to the output unaided by the inverter.
If the incoming two-leg shore power is true split phase (120 on each leg, 240 volts between the hots), then it will be handled as described above. However if the incoming shore power has 0 volts between the hots, then only L1 is used. L2 is ignored and disconnects. I'm not sure what happens with two legs of 3-phase power where there would be 120 degrees difference between the legs and 208 volts between the two hots.
I'm researching the MultiPlus-II 12|3000|120-50 2x120V and came across your question. Hopefully it's not poor etiquette to answer an old unanswered post.
From the MultiPlus manual:
When an AC source is available, the MultiPlus will feed through the AC to its output. The output will therefore mirror the AC input.
...
Any 240V loads will therefore be supplied only when the MultiPlus is supplied by a split-phase AC source. This prevents heavy
loads such as water heaters or 240V air conditioners from discharging the battery.
It seems the situation you describe is the intended behavior for the MultiPlus when fed by 120V single phase. Perhapps the L2 from shore power isn't actually hot or phased correctly.
