Could an electromatnetic pulse weapon (EMP) bring about a wide-spread power outage
The overall effectiveness of an EMP weapon is controlled by the following factors:
For electronic or electrical equipment to be affected, the EMP weapon would have to detonate above the visual horizon. For instance an electromagnetic pulse weapon detonated 300 miles above Kansas would affect most of the United States, although the West Coast would be less affected due to the interference of the Rocky Mountains.
There is some concern that a rogue terrorist state might use an EMP device. Fortunately the technical difficulty in delivery of the device may limit the threat to those larger national powers that have the ability to employ a long-range missile as a delivery device. However a high altitude detonation just off shore could devastate the entire coastal region and perhaps up to a thousand miles inland.
Due to the possibility of an EMP detonation by terrorists in a large urban city, many businesses have moved valuable assets outside of the city, or have taken steps to protect vital equipment from EMP. Initially research showed that the overall effects of a widespread EMP burst over a modern industrialized nation would be to turn that country back a hundred years. While that worst case scenario is probably not all that accurate according to more recent studies, there is still need for concern.
Is there something that the average citizen can do to provide EMP protection for their assets? One method is using the Faraday cage to provide EMP shielding for valuable electronics in the event of an EMP weapon detonation. Just remember, while some electronics might be useful to have still working after an EMP attack, having a working cell phone will be pretty useless when the necessary infrastructure may not be working.
EMP Shielding - Things you can do to shield valuable electronics from an EMP.
Faraday Cage - How to use a Faraday cage or box to beat an EMP.