When you are resetting circuit breakers or changing fuses to often. When you turn on your air conditioner and the lights dim in the room. When your lights flicker or go on and off. When you can smell electricity burning. When you have six electronic devises going into one outlet in back of your electronics center. When you have receptacle outlets overburdened by multi-plug strips. When a three-prong plug needs a two-prong adapter. If you have to run extension cords to plug in electrical devises.
To get answers to more questions about your electrical system see: Master Electric FAQs