Sometimes you need an inrush limiter with visual indication. https://tacobelllabs.net/@connections/113710038360178726
@philpem synchronizing too
@DeltaWye I feel like you need to explain this one, I'd expect you'd normally use a synchroscope for that.
@philpem You can use the brightness of a set of lightbulbs to verify synchronism. Each bulb is across the same phase letter on the two systems.
For a three phase system once the voltages, frequency, and rotation on the two sets of three phases match, the bulbs will all dim and then go out. Then you can sync.