Seems like almost all the fixtures we put in have gone to universal voltage ballasts; able to be used with 120 or 277. I was just curious about what goes on inside the ballast. Perhaps a single winding with different voltage points? How would it distinguish between voltages or would it matter?
One of the main things that got me thinking about it was that I was thinking of temporarily firing one up on 120 and then later changing to 277. I would think you could do that with no problems, but just wanted to be sure.
We are extremely busy by the way, lots of overtime. Hope you guys are doing great.

You should be OK.

"AccuStart® offers installer-friendly universal input voltage (108–305 volts)"

On a magnetic HID ballast, do not try 277V on anything other than the 277V tap. It's a completely different beast.

I don't know this for sure, but I'd look into the possibility of those universal ballasts being burned into it's initial voltage. I don't know what makes me think this, may have been a conversation in passing with a rep about them. But I was under the impression that once they were wired one voltage, that was it.