Backup power and grid power in same outlet box. Any issues?

[Q-Dog]

I have run some new circuits and outlets for backup power in the house. No issues there. But I have one outlet in a weird spot so instead of adding a new box and outlet I ran the new backup romex into the existing box and capped and taped off the old wire. Then I started wondering can I separate the outlet and run grid to one half and backup to the other half? And if I were do that, should the grounds from the grid circuit and the backup circuit be tied together on the same outlet?

My inverter/charger has an internal relay to switch grounding in and out depending on whether or not it is connected to grid. That seems to be working fine. My cheap plug-in circuit tester says the wiring and grounds are working correctly when the inverter/charger is grid connected and when disconnected from the grid.

 

[svetz]

...can I separate the outlet and run grid to one half and backup to the other half?

Yes, it's called a split-circuit receptacle; you just need to cut the tab (videos). You can test it's working correctly before installing it with an ohm meter, the two hot prongs (narrower slots if wired correctly) should have infinite resistance between them.

And if I were do that, should the grounds from the grid circuit and the backup circuit be tied together on the same outlet?
My inverter/charger has an internal relay to switch grounding in and out depending on whether or not it is connected to grid. That seems to be working fine. My cheap plug-in circuit tester says the wiring and grounds are working correctly when the inverter/charger is grid connected and when disconnected from the grid.

Use the ground wire that always connected, or both if it's either/or. If ground is never connected while on the inverter, you should dig into that as it's not doing its job at keeping you safe. That "Ground" (confusing as there's a bunch of things ground can refer to) isn't about the grid, it's about providing a short-circuit path so the breaker trips.

 

[Q-Dog]

Thanks. I didn't know what to call them but I remember installing an outlet once where one half was on a switch and the other half was live all the time. Just had to break off the tabs.

I guess the question is, is it wise (or up to code) to run circuits from 2 separate systems in the same outlet box. Not sure what if anything happens if the 2 separate circuit grounds get connected together at the split outlet.

My inverter/charger is grounded through the input circuit when connected to the grid, and the chassis is also grounded. I have seen my cheap circuit tester lights flicker to fault mode for a split second then show normal again when I pull the input to the charger and the relay does whatever it does inside.

 

[Supervstech]

As long as the wiring is connected properly, there isn’t anything in the code about it, but it may be easier to remember what is where in separate boxes.
At a minimum, I would label the outlet CAUTION, separate feeds, voltage present when one breaker is off...
And Label both circuits well.

 

[Q-Dog]

Good idea with the labeling. Thanks. I'll think about it some more. Might be safer to install another outlet in a more convenient location anyway. So far I have installed gray outlets and faceplates for the backup circuits, while all the original grid outlets are white. If I split this one it might get confusing.