Looking at the distribution panel or service panel can provide clues to the causes of power quality problems:

• Look for other loads on a shared panel that could be causing impulses, sags, or harmonic distortion.
• Assess the overall condition of the distribution panel (age, maintenance, condition)
• Check for loose connections, missing grounds, and other wiring faults
• Is the panel lightly loaded? overloaded?
• Is the panel a 3 Wire (Delta) and the load requires a 4 Wire (Wye)?
• Look for other signs of power quality problems - TVSS, transformers, hand-written notes, power conditioners - in the vicinity of the panel

If you are really lucky the panel will be labeled, the loads will be identified, and the documentation will be up to date. However, that's usually the exception!