Alternating Current- Dirty power is actually noise in the AC power lines, caused by electro-magnetic interference (EMI) and radio frequency interference (RFI). EMI is caused by electrical interferences from appliances, especially those that use motors (copying machines, air conditioners, refrigerators, washing machines and vacuum cleaners). RFI is caused by interference from radio devices such as cordless phones, microwave ovens, cell phones and others. The myriad electrical wires are usually not shielded and are affected by RFI and EMI interference. The solution is EMI/RFI filtering built into many power protection devices, which filters out noise in the AC power line and provides clean power to connected components.