You are correct. A panel supplied by a separately derived system (SDS) is generally considered a subpanel.Here's why: Service Panel

A service panel is the first point of distribution for electricity from the utility. It's directly connected to the utility's transformer and is where the main disconnect is located.

Separately Derived System (SDS)

An SDS, such as a generator, solar inverter, or transformer, creates its own electrical source that is electrically isolated from the main service.

Panel Supplied by SDS

The panel connected to the output of an SDS receives power from that system, not directly from the utility. Therefore, it's a downstream distribution point and acts as a subpanel of the SDS.

Key Considerations



Grounding

The grounding requirements for a panel supplied by an SDS are different from a service panel. The neutral must be bonded to ground at the SDS source (e.g., at the generator or transformer) and not in the subpanel. This prevents parallel neutral paths.

Overcurrent Protection

Proper overcurrent protection is vital for both the SDS and the panel it supplies.

Labeling

Clearly label the panel as being supplied by a separately derived system (e.g., "Generator Panel," "Solar Inverter Panel").*

NEC Compliance

Always consult and comply with the National Electrical Code (NEC) and local codes for specific requirements.

In Summary:

If a panel gets its power from something other than the utility's service entrance (e.g., a generator, solar inverter, or transformer), that something is a Separately Derived System, and the panel it feeds is a subpanel fed by that SDS. Flag for review