Two Pole VS Three Pole Safety Switch

[Mike6622]

I have a subpanel that I would like to power from either grid or inverter power. Can I use a 2 pole double throw safety switch or do I need to utilize a 3 pole switch to throw the neutral as well? The inverter power is only supplied by panels and batteries (grid input will be left unused).

 

[Zwy]

Double throw works as long as N-G bond is not at the inverter.

A 3 pole is used on something like my LV6548 where the inverter dynamically bonds N-G in the inverter. The neutral is switched at the 3 pole in order to have only one N-G bond present. This prevents objectionable current on G.

Ensure the sub panel is not N-G bonded.

 

[Mike6622]

Double throw works as long as N-G bond is not at the inverter.

A 3 pole is used on something like my LV6548 where the inverter dynamically bonds N-G in the inverter. The neutral is switched at the 3 pole in order to have only one N-G bond present. This prevents objectionable current on G.

Ensure the sub panel is not N-G bonded.

Thanks for the response. If I wanted to add a second sub panel would the same concept apply? Can I run panel One on the grid and panel Two on the inverter at the same time?

 

[Zwy]

Regarding your diagram, you don't need the extra EGC wires. Just run a EGC from subpanel grounding busbar to subpanel grounding busbar.

The problem will be the neutral. For example if one subpanel is on grid and the other subpanel is on inverter power. As you will not use grid power input to the inverter, there is the issue of phasing. The 18Kpv will do grid assist for large loads but I'm not certain it does shift to grid phase when this occurs. I'd contact @Markus_EG4 regarding that aspect. Personally, I wouldn't do it for the simple fact you can switch loads off in a large subpanel if you are in a grid down situation. I would probably just use a double throw in order to bypass the 18Kpv entirely if I needed to, for example work on the solar system/inverter and run grid power to the 18Kpv. That gives the option to power loads thru grid or 18Kpv with the settings/app.

Just remember that when using either an interlock or a double throw there is a delay in switching. This is to prevent cross phasing. As such the switch is not seamless and any loads will lose power momentarily. Clocks, computers without a UPS will shutdown. It is not seamless like an inverter that switches like a UPS.

 

[Hedges]

2-pole switch can be used. Both ground and neutral bonding can come from grid connection.
But neutral and ground should travel through same conduit or cable as L1 and L2, with all four wires close together except where they spread just to connects to switches, breakers, etc. Not going around the outside as you show.

One way to accomplish that is a Tee conduit to switch, so L1 and L2 from both grid and inverter go into switch through same conduit, also come back out of switch to load through same conduit. Then neutral doesn't go through switch. Ground does connect to switch.

Alternately, Neutral does go through the box which contains switch. L1 and L2 from grid and inverter both enter switch, same or different conduit. Neutral from both connect to an unswitched terminal in the box, while L1 and L2 from each goes to its switch terminal. Ground from each goes to a separate ground terminal in box. All wires L1, L2, N, G leave box (can be a third conduit) to load.

That's just about the switch. If inverter has auto-transformer (especially if it is a 240V only inverter with external autotransformer, that is a different can of worms, not addressed here.

Many inverters have grid input and output, in which case that performs the switching, and you don't need to add one for on/off grid operation.
What you can do is use an interlocked "generator" breaker in the sub-panel to manually bypass the inverter in the event it is disconnected for repair.