question

halfwalker avatar image

Using a Quattro 48/10000 230V with Autotransformer in US residential 240V split phase

I was originally asking about design consideration between using one large inverter or two smaller inverters. Then got onto a bit of the design using one large inverter, but that wasn't really pertinent to the Subject for tha thread.

https://community.victronenergy.com/questions/58759/choosing-between-one-large-inverter-or-two-smaller.html

So I'm re-asking the one-inverter-autotransformer question here in a dedicated thread. Has anyone set up a 230V Quattro with Autotransformer in a US residential setup ?

I'm envisioning a setup as follows :

  • Main panel : 100A breaker to Quattro AC1-in
  • Main panel : 100A breaker to sub-panel 100A breaker with interlock
  • Quattro AC1-out to Autotransformer
  • Autotransformer AC-out 120-0-120 hot-neutral-hot to sub-panel 100A breaker with interlock

The interlocked breakers are a back-feed setup for the sub-panel. Only ONE breaker can be on, the other must be off. So the sub-panel is fed by EITHER the 100A from the main panel, OR the AC-out from the Autotransformer. For example

https://media.suthlbr.com/products/images/21125/QO48M60DSGPSTR.jpg

In the US, there can be only neutral/ground bonding point, it must in the main service panel. So the GND relay in the Quattro should be disabled, and the GND relay in the Autotransformer should also be disabled. This way, regardless of whether the sub-panel is fed from the main panel or from the Autotransformer, the neutral/ground bond will only be in the main panel.

The created neutral from the Autotransformer is connected to the neutral bar in the sub-panel, which connects to the neutral bar in the main panel, where the final neutral/ground bond is made.

During an outage, power to the Quattro comes from a 240V generator, using only the L1/L2 hot legs. The neutral is not connected, so it acts just like the connection from the main panel.

Does this all make sense ? Is it correct for a US residential install ?

https://www.autodraw.com/share/IE7PDGNCPO0V

MultiPlus Quattro Inverter ChargerAutotransformersplit phase
1598019251497.png (732.2 KiB)
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Is there anyone out there using a Quattro 48/10000 230V with Autotransformer in a US residential setup ? The setup above looks like it should work fine, and be safe.

The sub-panel is fed from either the Autotransformer during normal operation, or from the main panel when the inverter/autotransformer setup is taken out of service via the interlocked breakers. The neutral from the Autotransformer passes all the way back to the main panel where the neutral/ground bond is.

Are there any issues or problems or safety things for this ?

I made the diagram a little clearer with regards to the interlocked backfeed breakers in the subpanel.

Is this a valid design for use in a USA residential 240V split-phase ?

3 Answers
Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

@Halfwalker, neither the Quattro nor the Autotransformer are UL-Listed, so I don't believe you'll be able to legally do this in the US.

Please contact your local building department as well as a licensed electrician in your jurisdiction and discuss this with them.

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Hrm - I thought that was only if you were doing a grid-tie setup. This wouldn't be selling back to the grid, and only supplying an isolated sub-panel.

That said, dang it, I'll bet insurance would look askance at having a non-UL listed setup. Which is a shame, that lack of UL listing is probably driving lots of potential customers away.

Come on Victron - get it done !

agillis avatar image
agillis answered ·

IEC is just as good of a safety certification as UL so Victron stuff is fine.

Also UL is not a legal requirement in the US! There is plenty of non UL equipment available here and your insurance company will still pay out if your house burns down.



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henry-cabrera avatar image
henry-cabrera answered ·

i have same installation in my residence with exception that my inverter also takes solar power from PV panels and batteries. I did not wire the ground relay either because the autotransformer neutral is also connected to the subpanel and then to the main panel neutral where is finally bonded to ground. My problem: the transformer breaker trips from time to time (not always) when the inverter makes the transfer from battery power to utility power. Can someone enlighten me on the nature of the trip and ways to resolve it?

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