I'm seeking some guidance on how to treat transformers when included in a
PV system.

Specific system details:
- (3x) SolarEdge 33.3 inverters combined in a 200A panel
- 480/208 transformer to be installed between 200A panel and main
distribution panel (service is 208 wye)

My questions:

- Is there any consensus on what circuit is considered the "primary" and
which is the "secondary" in this type of scenario?
   - NEC 690.9(D) speaks of "considering first one side of the transformer,
then the other side of the transformer, as the primary". Is this relevant?
i.e. Is it possible for both sides of the transformer to be labeled as a

- I understand that 450.4(A) requires overcurrent protection on the "input
conductors" (aka "primary conductors"?), correct? Must we provide
overcurrent protection on the "other" side in the above scenario?
   - We were originally planning to land each inverter output on a 50A
breaker inside a 200A main lug panel - must we also include a main breaker?

- How do we size the grounding conductors on either side of the transformer?
   - Is the grounding conductor between MDP and transformer considered an
EGC (250.122)?
   - Is the inverter-side of the transformer considered a separately
derived system, in which case the grounding conductor would be considered a
GEC (250.102(C)(1))?

Thanks for any advice!

Corey Shalanski
Joule Energy
New Orleans, LA
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