Harmonics

I have a problem in my plant. The power factor is .98+.
the system is 3 phase 4 wire. one leg is 208 V against the
neutral. The high leg powers 3 5 HP air compressors and four
one horse power balancer. In the summer the AC is connected also. I am drawing about 5 to 7 KW on each 120/240 volt
leg. Why should I get 15-12 and 7 % harmonics 0n the
amperage ?
Any help is appreciated.
LiteIt@ptd.net
Thank you.

PS: air compressors, balancer and A/C are three phase.
The ground is OK

 

[jbartos]

Please, what is the nominal 3phase 4wire system voltage and from what kind of source/circuits, to clarify 208V, 240V and 120V occurrence?