Breaker box and critical loads sub panel approach

[Butch11]

Hi-- Does it make sense for the main panel that is grid powered to be electrically isolated from the critical loads sub panel which is powered by the output of the solar hybrid inverter?

 

[OffGridForGood]

Depends what you are tying to achieve.
A typical CLP (critical loads panel) will have both grid an off grid power supplies available. The off grid part can be solar battery system or a standby generator.
If conditions allow, the CLP may run off grid, but in the case of poor alternate power supply (cloudy days) you can easily switch back to utiltiy power.
A popular CLP like the Reliance units, are never "isolated" since they rely on a shared common neutral and ground to function.

 

[hwy17]

Normally you want the CLP to share it's ground and neutral with the main panel, with a ground neutral bond only in the main panel.

 

[Butch11]

Yes, I should have been more precise. What I meant is that the main panel is not feeding power to the CLP. The CLP is only fed by the hybrid inverter which does have the grid as one of its input power sources. So, when the grid goes down, only the circuits on the CLP are powered assuming that either the solar panels, the batteries, or a backup generator are providing energy to the hybrid inverter.

 

[OffGridForGood]

What I meant is that the main panel is not feeding power to the CLP. The CLP is only fed by the hybrid inverter which does have the grid as one of its input power sources. So, when the grid goes down, only the circuits on the CLP are powered assuming that either the solar panels, the batteries, or a backup generator are providing energy to the hybrid inverter.

in the case of the off grid system as the sole power supply to the CLP, with utility power supply (to the inverter) then if there is a pass through option, on the inverter, then the grid could be directly tied to the CLP.

However if the utility power is only to a battery charger - ie like the EG4 Chargeverter, and not to the inverter, then there is no pass through option available, and the CLP is never tied to the utility. In this case you can say it is Isolated from the utility.

 

[sumpower]

Electrically isolated? Where I am located the ground of any system that supplies power to the same structure needs the ground of each system tied together at some point.
The Neutral and the load conductors from the inverter and on the CLP are isolated though.