I suspect you are power a load with a relatively low power factor. This draws more current. I suspect this is what the load percentage reflects.
Thank you for your reply, Elk. My loads are the tube amps with big transformers so I guess they draws more current. The P5 displays current as 1.74A. Output voltage is 225V, so usage in kVA is 225*1.74 = 391.5 (kVA) (power factor = 291/391.5 = 0.74).
With the load% as 32%, I believe the max kVA by P5 is 391.5*100/32 ~1200 kvA. Is 1200kVA the rating of P5? Can you please confirm? Thanks.