Hertz Irregularity

Have you ruled out a defective testing device by using a different (second) testing device?

20 to 900 seems to me to be some some very dramatic swings.

Is any equipment in the plant malfunctioning?

Probably could not hurt to test the 480 also for comparison.

At my wonderful company no one else has a meter with that function.but me.no the 480hertz is around 85 to 110hz. I can't see any other machines acting funky

Have you gotten those fluctuations on the 480 volt side in the past?

Given that no equipment is acting up and the read is not as varied on the 480, my gut says your meter may be defective.

"Conditioned power" like a UPS device? Many UPS devices do NOT put out perfect sign waves. If not a UPS and a true condition power unit then how did you measure it with a scope or frequency meter. There may be harmonics you are measuring not the fundamental. Use a scope with an 1:1 isolation transformer because the scope ground lead goes to Earth Ground and you may hook up to the Hot lead. You can be fooled by using just a frequency meter due to how it measures the trigger point. What about before the power conditioner what frequency is that. Or call your power company because I know someone in the power company and the 60 Hz is kept very stable. And my math says 3 cycles of 60Hz = 20Hz and 15 cycles of 60 Hz is 900 Hz. And it is exactly that number with my HP calculator 20.00 and 900.00. Check with a scope like I said and trigger on "Line".

I had the power company come out and check my sub station and turns out my regulators are jacked up. Thanks for input guys