I have a 208-277 photocell on a LED wallpack and the supply voltage is reading 286v. When I cover the photocell the light does not come on but if I disconnect the neutral wire from the B phase and reconnect it the light comes on for 10 secs like normal. The issue is the photocell is covered and the light still turns off. Will the incoming voltage of 286 make the photocell not work correctly because it is out of the voltage range or is it just a bad photocell.

Do you have line and load reversed?

That voltage of 286 is actually fine. I would be more concerned if the line and low are backwards like twh stated. You probably have it figured out by now.

The OP said 'if I disconnect the neutral wire from 'b' phase.....' ??

IS that a mis-statement, or does he have 480 volt going to the PC??

Black to line (phase a, b, or c), white to neutral, and red to load.

I would like to ask OP what sort of "photo-cell" he is actually using.
It could be that the photo-cell is either set up in the wrong mode or the sensitivity level is set wrong, these things are not "plug and play".
At the end of the day all these things are is a voltage in through two terminals and a single change-over contact on the output (NO/NC), with a common terminal