Three amps at 120V is 360 voltamperes, but these days the fixture should have fairly high power factor, so probably under 200 voltamperes [under 2 amps] would be more reasonable.
Contact the manufacturer for a specific rating...they may have a web site with electrical ratings of their products.
The fixture should be hotter than blazes of it's actually using that much power. Make darn you have an accurate meter, that the right tap is used on the ballast and that the line voltage is in range.
