Bypass Wiring - double as AC disconnect by paralleling Sol-Ark Load output

[Thomas_]

Hi,

My utility requires a visible open AC disconnect to separate the inverter from the utility. I also want a bypass switch to bypass Solar and use grid only as an option. Sol-Arks wiring schematic in the manual shows the inverter output as being switched through the transfer switch. This would mean I need to also install a second 200A disconnect on the input to meet the utility requirement.

Question: See my attached single line. Feed the grid input into the center of the transfer switch. One side of the transfer switch feeds the sol-ark input (normal operation), the other side of the transfer switch connects to house load as well as the sol-ark load output. Since this side of the transfer switch is disconnected in normal operation there should be no issue with the inverter.
My concern is in bypass mode the grid is directly connected to load, but also to the sol-ark load output (grid side is disconnected). My concern is if there are potential issues with the inverter in this bypass mode. I think any issues could be eliminated by switching the load side breaker off, but if this sequence was not followed could the inverter be damaged? Any other issues or concerns you see?

 

[crossy]

Connecting the grid to the Load terminals of the inverter is very likely to send it into low-earth orbit! Avoid that possibility at all costs.

For that matter, does the transfer switch meet the requirements of a disconnect?

 

[Thomas_]

The disconnect needs to be 200A due to the 200A feedthrough on the sol ark. The transfer switch meets the disconnect requirements since it is visible open in the off position.

I was thinking about this a little more, and in the event the transfer switch is switched off the sol-ark would go into offgrid backup mode, when the transfer switch is then closed into backup it will connect grid to load while the sol-ark is feeding that load. Disconnecting the load breaker on the sol-ark would prevent this but is a manual step - it could likely cause an error on the sol-ark but I don't see how it could damage anything.

 

[crossy]

Yeah, understand the disconnect situation.

I still wouldn't want to accidentally connect the effectively zero source impedance of the grid to the non-zero source impedance of the inverter, there would only be one winner. Whether the inverter could react fast enough to avoid damage is unknown.

There are a number of stories on here about people who accidentally connected grid to inverter output (not necessarily sol-ark), none had happy endings.

Does your transfer switch have Aux contacts that you could use to control a contactor on the Load output so it was only energised when the switch was in the "Normal" (grid feeding the inverter) position?

To be honest, I'd just bite the bullet and install the disconnect, it's simple and is what any inspector would be used to seeing. Inspectors really don't like "unusual" installations.

 

[Thomas_]

Yeah, understand the disconnect situation.

I still wouldn't want to accidentally connect the effectively zero source impedance of the grid to the non-zero source impedance of the inverter, there would only be one winner. Whether the inverter could react fast enough to avoid damage is unknown.

There are a number of stories on here about people who accidentally connected grid to inverter output (not necessarily sol-ark), none had happy endings.

Does your transfer switch have Aux contacts that you could use to control a contactor on the Load output so it was only energised when the switch was in the "Normal" (grid feeding the inverter) position?

To be honest, I'd just bite the bullet and install the disconnect, it's simple and is what any inspector would be used to seeing. Inspectors really don't like "unusual" installations.

Thanks, looked at some other threads about accidental back feed letting the smoke out of inverters. I don't want to risk it and will switch to the sol ark recommended transfer switch configuration

 

[67King]

You need a fused disconnect between the meter and the transfer switch. You need to rewire your transfer switch such that the switched part (the center, the part your diagram shows connected to grid) goes to the panel(s), and can be moved from grid ("up") to inverter ("down"). The grid to inverter line is not switched, it is directly wired.

This is page 9 of the manual (p10 on the PDF).