How often do these disturbances occur?

Because we use so many appliances and equipment such as refrigerators, pumps, heating and air conditioning systems all the time, disturbances happen frequently. A 17-month study done by IBM in 49 cities across the country found that an average of 128.3 disturbances happened in each monitored facility every month. Most were surges that did not cause immediate damage, but which could wear down equipment over time.