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Grid connections

Each feed is one supply from the street. Phase, amps, voltage, network, and retailer sit on that feed.

Open Settings → Building & Grid → Grid.
Add a feed. A site can have more than one, for example a primary supply and a second feed.
Set the phase (single or three), the amperage, and the voltage.
Assign the network provider and the energy retailer for that feed.

The retailer plan, including a wholesale API key, is stored on the feed. Prices you fetch belong to that supply, not to the whole account.