This morning I opened up my main breaker box to replace the old doorbell transformer. I thought this would be a straightforward job but didn't account for confusing wiring of the old transformer setup.
The new transformer has the typical black, white and green (ground) wires. The old transformer has two blacks and a green (photos attached).
Even more confusing is the way those old wires are connected. One of the black wires and the green are connected together directly to the main box. The other black wire is connected to other black wires via a wire nut.
How can I know where to plug in my black and white wires? Should I just cap the new ground wire with a wire nut or attach it somewhere in the box? Thanks for your help!